LCOV - code coverage report
Current view: directory - other-licenses/snappy/src - snappy.cc (source / functions) Found Hit Coverage
Test: app.info Lines: 424 289 68.2 %
Date: 2012-06-02 Functions: 46 31 67.4 %

       1                 : // Copyright 2005 Google Inc. All Rights Reserved.
       2                 : //
       3                 : // Redistribution and use in source and binary forms, with or without
       4                 : // modification, are permitted provided that the following conditions are
       5                 : // met:
       6                 : //
       7                 : //     * Redistributions of source code must retain the above copyright
       8                 : // notice, this list of conditions and the following disclaimer.
       9                 : //     * Redistributions in binary form must reproduce the above
      10                 : // copyright notice, this list of conditions and the following disclaimer
      11                 : // in the documentation and/or other materials provided with the
      12                 : // distribution.
      13                 : //     * Neither the name of Google Inc. nor the names of its
      14                 : // contributors may be used to endorse or promote products derived from
      15                 : // this software without specific prior written permission.
      16                 : //
      17                 : // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
      18                 : // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
      19                 : // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
      20                 : // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
      21                 : // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
      22                 : // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
      23                 : // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
      24                 : // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
      25                 : // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
      26                 : // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
      27                 : // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
      28                 : 
      29                 : #include "snappy.h"
      30                 : #include "snappy-internal.h"
      31                 : #include "snappy-sinksource.h"
      32                 : 
      33                 : #include <stdio.h>
      34                 : 
      35                 : #include <algorithm>
      36                 : #include <string>
      37                 : #include <vector>
      38                 : 
      39                 : 
      40                 : namespace snappy {
      41                 : 
      42                 : // Any hash function will produce a valid compressed bitstream, but a good
      43                 : // hash function reduces the number of collisions and thus yields better
      44                 : // compression for compressible input, and more speed for incompressible
      45                 : // input. Of course, it doesn't hurt if the hash function is reasonably fast
      46                 : // either, as it gets called a lot.
      47           35465 : static inline uint32 HashBytes(uint32 bytes, int shift) {
      48           35465 :   uint32 kMul = 0x1e35a7bd;
      49           35465 :   return (bytes * kMul) >> shift;
      50                 : }
      51           31957 : static inline uint32 Hash(const char* p, int shift) {
      52           31957 :   return HashBytes(UNALIGNED_LOAD32(p), shift);
      53                 : }
      54                 : 
      55            3674 : size_t MaxCompressedLength(size_t source_len) {
      56                 :   // Compressed data can be defined as:
      57                 :   //    compressed := item* literal*
      58                 :   //    item       := literal* copy
      59                 :   //
      60                 :   // The trailing literal sequence has a space blowup of at most 62/60
      61                 :   // since a literal of length 60 needs one tag byte + one extra byte
      62                 :   // for length information.
      63                 :   //
      64                 :   // Item blowup is trickier to measure.  Suppose the "copy" op copies
      65                 :   // 4 bytes of data.  Because of a special check in the encoding code,
      66                 :   // we produce a 4-byte copy only if the offset is < 65536.  Therefore
      67                 :   // the copy op takes 3 bytes to encode, and this type of item leads
      68                 :   // to at most the 62/60 blowup for representing literals.
      69                 :   //
      70                 :   // Suppose the "copy" op copies 5 bytes of data.  If the offset is big
      71                 :   // enough, it will take 5 bytes to encode the copy op.  Therefore the
      72                 :   // worst case here is a one-byte literal followed by a five-byte copy.
      73                 :   // I.e., 6 bytes of input turn into 7 bytes of "compressed" data.
      74                 :   //
      75                 :   // This last factor dominates the blowup, so the final estimate is:
      76            3674 :   return 32 + source_len + source_len/6;
      77                 : }
      78                 : 
      79                 : enum {
      80                 :   LITERAL = 0,
      81                 :   COPY_1_BYTE_OFFSET = 1,  // 3 bit length + 3 bits of offset in opcode
      82                 :   COPY_2_BYTE_OFFSET = 2,
      83                 :   COPY_4_BYTE_OFFSET = 3
      84                 : };
      85                 : 
      86                 : // Copy "len" bytes from "src" to "op", one byte at a time.  Used for
      87                 : // handling COPY operations where the input and output regions may
      88                 : // overlap.  For example, suppose:
      89                 : //    src    == "ab"
      90                 : //    op     == src + 2
      91                 : //    len    == 20
      92                 : // After IncrementalCopy(src, op, len), the result will have
      93                 : // eleven copies of "ab"
      94                 : //    ababababababababababab
      95                 : // Note that this does not match the semantics of either memcpy()
      96                 : // or memmove().
      97               8 : static inline void IncrementalCopy(const char* src, char* op, int len) {
      98               8 :   DCHECK_GT(len, 0);
      99              93 :   do {
     100              93 :     *op++ = *src++;
     101                 :   } while (--len > 0);
     102               8 : }
     103                 : 
     104                 : // Equivalent to IncrementalCopy except that it can write up to ten extra
     105                 : // bytes after the end of the copy, and that it is faster.
     106                 : //
     107                 : // The main part of this loop is a simple copy of eight bytes at a time until
     108                 : // we've copied (at least) the requested amount of bytes.  However, if op and
     109                 : // src are less than eight bytes apart (indicating a repeating pattern of
     110                 : // length < 8), we first need to expand the pattern in order to get the correct
     111                 : // results. For instance, if the buffer looks like this, with the eight-byte
     112                 : // <src> and <op> patterns marked as intervals:
     113                 : //
     114                 : //    abxxxxxxxxxxxx
     115                 : //    [------]           src
     116                 : //      [------]         op
     117                 : //
     118                 : // a single eight-byte copy from <src> to <op> will repeat the pattern once,
     119                 : // after which we can move <op> two bytes without moving <src>:
     120                 : //
     121                 : //    ababxxxxxxxxxx
     122                 : //    [------]           src
     123                 : //        [------]       op
     124                 : //
     125                 : // and repeat the exercise until the two no longer overlap.
     126                 : //
     127                 : // This allows us to do very well in the special case of one single byte
     128                 : // repeated many times, without taking a big hit for more general cases.
     129                 : //
     130                 : // The worst case of extra writing past the end of the match occurs when
     131                 : // op - src == 1 and len == 1; the last copy will read from byte positions
     132                 : // [0..7] and write to [4..11], whereas it was only supposed to write to
     133                 : // position 1. Thus, ten excess bytes.
     134                 : 
     135                 : namespace {
     136                 : 
     137                 : const int kMaxIncrementCopyOverflow = 10;
     138                 : 
     139                 : }  // namespace
     140                 : 
     141             999 : static inline void IncrementalCopyFastPath(const char* src, char* op, int len) {
     142            4078 :   while (op - src < 8) {
     143            2080 :     UNALIGNED_STORE64(op, UNALIGNED_LOAD64(src));
     144            2080 :     len -= op - src;
     145            2080 :     op += op - src;
     146                 :   }
     147            2997 :   while (len > 0) {
     148             999 :     UNALIGNED_STORE64(op, UNALIGNED_LOAD64(src));
     149             999 :     src += 8;
     150             999 :     op += 8;
     151             999 :     len -= 8;
     152                 :   }
     153             999 : }
     154                 : 
     155            3066 : static inline char* EmitLiteral(char* op,
     156                 :                                 const char* literal,
     157                 :                                 int len,
     158                 :                                 bool allow_fast_path) {
     159            3066 :   int n = len - 1;      // Zero-length literals are disallowed
     160            3066 :   if (n < 60) {
     161                 :     // Fits in tag byte
     162            3066 :     *op++ = LITERAL | (n << 2);
     163                 : 
     164                 :     // The vast majority of copies are below 16 bytes, for which a
     165                 :     // call to memcpy is overkill. This fast path can sometimes
     166                 :     // copy up to 15 bytes too much, but that is okay in the
     167                 :     // main loop, since we have a bit to go on for both sides:
     168                 :     //
     169                 :     //   - The input will always have kInputMarginBytes = 15 extra
     170                 :     //     available bytes, as long as we're in the main loop, and
     171                 :     //     if not, allow_fast_path = false.
     172                 :     //   - The output will always have 32 spare bytes (see
     173                 :     //     MaxCompressedLength).
     174            3066 :     if (allow_fast_path && len <= 16) {
     175             831 :       UNALIGNED_STORE64(op, UNALIGNED_LOAD64(literal));
     176             831 :       UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(literal + 8));
     177             831 :       return op + len;
     178                 :     }
     179                 :   } else {
     180                 :     // Encode in upcoming bytes
     181               0 :     char* base = op;
     182               0 :     int count = 0;
     183               0 :     op++;
     184               0 :     while (n > 0) {
     185               0 :       *op++ = n & 0xff;
     186               0 :       n >>= 8;
     187               0 :       count++;
     188                 :     }
     189               0 :     assert(count >= 1);
     190               0 :     assert(count <= 4);
     191               0 :     *base = LITERAL | ((59+count) << 2);
     192                 :   }
     193            2235 :   memcpy(op, literal, len);
     194            2235 :   return op + len;
     195                 : }
     196                 : 
     197            1657 : static inline char* EmitCopyLessThan64(char* op, size_t offset, int len) {
     198            1657 :   DCHECK_LE(len, 64);
     199            1657 :   DCHECK_GE(len, 4);
     200            1657 :   DCHECK_LT(offset, 65536);
     201                 : 
     202            1657 :   if ((len < 12) && (offset < 2048)) {
     203            1600 :     size_t len_minus_4 = len - 4;
     204            1600 :     assert(len_minus_4 < 8);            // Must fit in 3 bits
     205            1600 :     *op++ = COPY_1_BYTE_OFFSET | ((len_minus_4) << 2) | ((offset >> 8) << 5);
     206            1600 :     *op++ = offset & 0xff;
     207                 :   } else {
     208              57 :     *op++ = COPY_2_BYTE_OFFSET | ((len-1) << 2);
     209              57 :     LittleEndian::Store16(op, offset);
     210              57 :     op += 2;
     211                 :   }
     212            1657 :   return op;
     213                 : }
     214                 : 
     215            1657 : static inline char* EmitCopy(char* op, size_t offset, int len) {
     216                 :   // Emit 64 byte copies but make sure to keep at least four bytes reserved
     217            3314 :   while (len >= 68) {
     218               0 :     op = EmitCopyLessThan64(op, offset, 64);
     219               0 :     len -= 64;
     220                 :   }
     221                 : 
     222                 :   // Emit an extra 60 byte copy if have too much data to fit in one copy
     223            1657 :   if (len > 64) {
     224               0 :     op = EmitCopyLessThan64(op, offset, 60);
     225               0 :     len -= 60;
     226                 :   }
     227                 : 
     228                 :   // Emit remainder
     229            1657 :   op = EmitCopyLessThan64(op, offset, len);
     230            1657 :   return op;
     231                 : }
     232                 : 
     233                 : 
     234            1970 : bool GetUncompressedLength(const char* start, size_t n, size_t* result) {
     235            1970 :   uint32 v = 0;
     236            1970 :   const char* limit = start + n;
     237            1970 :   if (Varint::Parse32WithLimit(start, limit, &v) != NULL) {
     238            1970 :     *result = v;
     239            1970 :     return true;
     240                 :   } else {
     241               0 :     return false;
     242                 :   }
     243                 : }
     244                 : 
     245                 : namespace internal {
     246            1837 : uint16* WorkingMemory::GetHashTable(size_t input_size, int* table_size) {
     247                 :   // Use smaller hash table when input.size() is smaller, since we
     248                 :   // fill the table, incurring O(hash table size) overhead for
     249                 :   // compression, and if the input is short, we won't need that
     250                 :   // many hash table entries anyway.
     251                 :   assert(kMaxHashTableSize >= 256);
     252            1837 :   size_t htsize = 256;
     253            3674 :   while (htsize < kMaxHashTableSize && htsize < input_size) {
     254               0 :     htsize <<= 1;
     255                 :   }
     256            1837 :   CHECK_EQ(0, htsize & (htsize - 1)) << ": must be power of two";
     257            1837 :   CHECK_LE(htsize, kMaxHashTableSize) << ": hash table too large";
     258                 : 
     259                 :   uint16* table;
     260            1837 :   if (htsize <= ARRAYSIZE(small_table_)) {
     261            1837 :     table = small_table_;
     262                 :   } else {
     263               0 :     if (large_table_ == NULL) {
     264               0 :       large_table_ = new uint16[kMaxHashTableSize];
     265                 :     }
     266               0 :     table = large_table_;
     267                 :   }
     268                 : 
     269            1837 :   *table_size = htsize;
     270            1837 :   memset(table, 0, htsize * sizeof(*table));
     271            1837 :   return table;
     272                 : }
     273                 : }  // end namespace internal
     274                 : 
     275                 : // For 0 <= offset <= 4, GetUint32AtOffset(UNALIGNED_LOAD64(p), offset) will
     276                 : // equal UNALIGNED_LOAD32(p + offset).  Motivation: On x86-64 hardware we have
     277                 : // empirically found that overlapping loads such as
     278                 : //  UNALIGNED_LOAD32(p) ... UNALIGNED_LOAD32(p+1) ... UNALIGNED_LOAD32(p+2)
     279                 : // are slower than UNALIGNED_LOAD64(p) followed by shifts and casts to uint32.
     280            4820 : static inline uint32 GetUint32AtOffset(uint64 v, int offset) {
     281            4820 :   DCHECK(0 <= offset && offset <= 4) << offset;
     282            4820 :   return v >> (LittleEndian::IsLittleEndian() ? 8 * offset : 32 - 8 * offset);
     283                 : }
     284                 : 
     285                 : // Flat array compression that does not emit the "uncompressed length"
     286                 : // prefix. Compresses "input" string to the "*op" buffer.
     287                 : //
     288                 : // REQUIRES: "input" is at most "kBlockSize" bytes long.
     289                 : // REQUIRES: "op" points to an array of memory that is at least
     290                 : // "MaxCompressedLength(input.size())" in size.
     291                 : // REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
     292                 : // REQUIRES: "table_size" is a power of two
     293                 : //
     294                 : // Returns an "end" pointer into "op" buffer.
     295                 : // "end - op" is the compressed size of "input".
     296                 : namespace internal {
     297            1837 : char* CompressFragment(const char* input,
     298                 :                        size_t input_size,
     299                 :                        char* op,
     300                 :                        uint16* table,
     301                 :                        const int table_size) {
     302                 :   // "ip" is the input pointer, and "op" is the output pointer.
     303            1837 :   const char* ip = input;
     304            1837 :   CHECK_LE(input_size, kBlockSize);
     305            1837 :   CHECK_EQ(table_size & (table_size - 1), 0) << ": table must be power of two";
     306            1837 :   const int shift = 32 - Bits::Log2Floor(table_size);
     307            1837 :   DCHECK_EQ(static_cast<int>(kuint32max >> shift), table_size - 1);
     308            1837 :   const char* ip_end = input + input_size;
     309            1837 :   const char* base_ip = ip;
     310                 :   // Bytes in [next_emit, ip) will be emitted as literal bytes.  Or
     311                 :   // [next_emit, ip_end) after the main loop.
     312            1837 :   const char* next_emit = ip;
     313                 : 
     314            1837 :   const size_t kInputMarginBytes = 15;
     315            1837 :   if (PREDICT_TRUE(input_size >= kInputMarginBytes)) {
     316            1701 :     const char* ip_limit = input + input_size - kInputMarginBytes;
     317                 : 
     318            2585 :     for (uint32 next_hash = Hash(++ip, shift); ; ) {
     319            2585 :       DCHECK_LT(next_emit, ip);
     320                 :       // The body of this loop calls EmitLiteral once and then EmitCopy one or
     321                 :       // more times.  (The exception is that when we're close to exhausting
     322                 :       // the input we goto emit_remainder.)
     323                 :       //
     324                 :       // In the first iteration of this loop we're just starting, so
     325                 :       // there's nothing to copy, so calling EmitLiteral once is
     326                 :       // necessary.  And we only start a new iteration when the
     327                 :       // current iteration has determined that a call to EmitLiteral will
     328                 :       // precede the next call to EmitCopy (if any).
     329                 :       //
     330                 :       // Step 1: Scan forward in the input looking for a 4-byte-long match.
     331                 :       // If we get close to exhausting the input then goto emit_remainder.
     332                 :       //
     333                 :       // Heuristic match skipping: If 32 bytes are scanned with no matches
     334                 :       // found, start looking only at every other byte. If 32 more bytes are
     335                 :       // scanned, look at every third byte, etc.. When a match is found,
     336                 :       // immediately go back to looking at every byte. This is a small loss
     337                 :       // (~5% performance, ~0.1% density) for compressible data due to more
     338                 :       // bookkeeping, but for non-compressible data (such as JPEG) it's a huge
     339                 :       // win since the compressor quickly "realizes" the data is incompressible
     340                 :       // and doesn't bother looking for matches everywhere.
     341                 :       //
     342                 :       // The "skip" variable keeps track of how many bytes there are since the
     343                 :       // last match; dividing it by 32 (ie. right-shifting by five) gives the
     344                 :       // number of bytes to move ahead for each iteration.
     345            2585 :       uint32 skip = 32;
     346                 : 
     347            2585 :       const char* next_ip = ip;
     348                 :       const char* candidate;
     349           14450 :       do {
     350           15806 :         ip = next_ip;
     351           15806 :         uint32 hash = next_hash;
     352           15806 :         DCHECK_EQ(hash, Hash(ip, shift));
     353           15806 :         uint32 bytes_between_hash_lookups = skip++ >> 5;
     354           15806 :         next_ip = ip + bytes_between_hash_lookups;
     355           15806 :         if (PREDICT_FALSE(next_ip > ip_limit)) {
     356            1356 :           goto emit_remainder;
     357                 :         }
     358           14450 :         next_hash = Hash(next_ip, shift);
     359           14450 :         candidate = base_ip + table[hash];
     360           14450 :         DCHECK_GE(candidate, base_ip);
     361           14450 :         DCHECK_LT(candidate, ip);
     362                 : 
     363           14450 :         table[hash] = ip - base_ip;
     364                 :       } while (PREDICT_TRUE(UNALIGNED_LOAD32(ip) !=
     365                 :                             UNALIGNED_LOAD32(candidate)));
     366                 : 
     367                 :       // Step 2: A 4-byte match has been found.  We'll later see if more
     368                 :       // than 4 bytes match.  But, prior to the match, input
     369                 :       // bytes [next_emit, ip) are unmatched.  Emit them as "literal bytes."
     370            1229 :       DCHECK_LE(next_emit + 16, ip_end);
     371            1229 :       op = EmitLiteral(op, next_emit, ip - next_emit, true);
     372                 : 
     373                 :       // Step 3: Call EmitCopy, and then see if another EmitCopy could
     374                 :       // be our next move.  Repeat until we find no match for the
     375                 :       // input immediately after what was consumed by the last EmitCopy call.
     376                 :       //
     377                 :       // If we exit this loop normally then we need to call EmitLiteral next,
     378                 :       // though we don't yet know how big the literal will be.  We handle that
     379                 :       // by proceeding to the next iteration of the main loop.  We also can exit
     380                 :       // this loop via goto if we get close to exhausting the input.
     381            1229 :       uint64 input_bytes = 0;
     382            1229 :       uint32 candidate_bytes = 0;
     383                 : 
     384            1312 :       do {
     385                 :         // We have a 4-byte match at ip, and no need to emit any
     386                 :         // "literal bytes" prior to ip.
     387            1657 :         const char* base = ip;
     388            1657 :         int matched = 4 + FindMatchLength(candidate + 4, ip + 4, ip_end);
     389            1657 :         ip += matched;
     390            1657 :         size_t offset = base - candidate;
     391            1657 :         DCHECK_EQ(0, memcmp(base, candidate, matched));
     392            1657 :         op = EmitCopy(op, offset, matched);
     393                 :         // We could immediately start working at ip now, but to improve
     394                 :         // compression we first update table[Hash(ip - 1, ...)].
     395            1657 :         const char* insert_tail = ip - 1;
     396            1657 :         next_emit = ip;
     397            1657 :         if (PREDICT_FALSE(ip >= ip_limit)) {
     398             345 :           goto emit_remainder;
     399                 :         }
     400            1312 :         input_bytes = UNALIGNED_LOAD64(insert_tail);
     401            1312 :         uint32 prev_hash = HashBytes(GetUint32AtOffset(input_bytes, 0), shift);
     402            1312 :         table[prev_hash] = ip - base_ip - 1;
     403            1312 :         uint32 cur_hash = HashBytes(GetUint32AtOffset(input_bytes, 1), shift);
     404            1312 :         candidate = base_ip + table[cur_hash];
     405            1312 :         candidate_bytes = UNALIGNED_LOAD32(candidate);
     406            1312 :         table[cur_hash] = ip - base_ip;
     407            1312 :       } while (GetUint32AtOffset(input_bytes, 1) == candidate_bytes);
     408                 : 
     409             884 :       next_hash = HashBytes(GetUint32AtOffset(input_bytes, 2), shift);
     410             884 :       ++ip;
     411                 :     }
     412                 :   }
     413                 : 
     414                 :  emit_remainder:
     415                 :   // Emit the remaining bytes as a literal
     416            1837 :   if (next_emit < ip_end) {
     417            1837 :     op = EmitLiteral(op, next_emit, ip_end - next_emit, false);
     418                 :   }
     419                 : 
     420            1837 :   return op;
     421                 : }
     422                 : }  // end namespace internal
     423                 : 
     424                 : // Signature of output types needed by decompression code.
     425                 : // The decompression code is templatized on a type that obeys this
     426                 : // signature so that we do not pay virtual function call overhead in
     427                 : // the middle of a tight decompression loop.
     428                 : //
     429                 : // class DecompressionWriter {
     430                 : //  public:
     431                 : //   // Called before decompression
     432                 : //   void SetExpectedLength(size_t length);
     433                 : //
     434                 : //   // Called after decompression
     435                 : //   bool CheckLength() const;
     436                 : //
     437                 : //   // Called repeatedly during decompression
     438                 : //   bool Append(const char* ip, size_t length);
     439                 : //   bool AppendFromSelf(uint32 offset, size_t length);
     440                 : //
     441                 : //   // The difference between TryFastAppend and Append is that TryFastAppend
     442                 : //   // is allowed to read up to <available> bytes from the input buffer,
     443                 : //   // whereas Append is allowed to read <length>.
     444                 : //   //
     445                 : //   // Also, TryFastAppend is allowed to return false, declining the append,
     446                 : //   // without it being a fatal error -- just "return false" would be
     447                 : //   // a perfectly legal implementation of TryFastAppend. The intention
     448                 : //   // is for TryFastAppend to allow a fast path in the common case of
     449                 : //   // a small append.
     450                 : //   //
     451                 : //   // NOTE(user): TryFastAppend must always return decline (return false)
     452                 : //   // if <length> is 61 or more, as in this case the literal length is not
     453                 : //   // decoded fully. In practice, this should not be a big problem,
     454                 : //   // as it is unlikely that one would implement a fast path accepting
     455                 : //   // this much data.
     456                 : //   bool TryFastAppend(const char* ip, size_t available, size_t length);
     457                 : // };
     458                 : 
     459                 : // -----------------------------------------------------------------------
     460                 : // Lookup table for decompression code.  Generated by ComputeTable() below.
     461                 : // -----------------------------------------------------------------------
     462                 : 
     463                 : // Mapping from i in range [0,4] to a mask to extract the bottom 8*i bits
     464                 : static const uint32 wordmask[] = {
     465                 :   0u, 0xffu, 0xffffu, 0xffffffu, 0xffffffffu
     466                 : };
     467                 : 
     468                 : // Data stored per entry in lookup table:
     469                 : //      Range   Bits-used       Description
     470                 : //      ------------------------------------
     471                 : //      1..64   0..7            Literal/copy length encoded in opcode byte
     472                 : //      0..7    8..10           Copy offset encoded in opcode byte / 256
     473                 : //      0..4    11..13          Extra bytes after opcode
     474                 : //
     475                 : // We use eight bits for the length even though 7 would have sufficed
     476                 : // because of efficiency reasons:
     477                 : //      (1) Extracting a byte is faster than a bit-field
     478                 : //      (2) It properly aligns copy offset so we do not need a <<8
     479                 : static const uint16 char_table[256] = {
     480                 :   0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002,
     481                 :   0x0003, 0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004,
     482                 :   0x0005, 0x0808, 0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006,
     483                 :   0x0007, 0x080a, 0x1007, 0x2007, 0x0008, 0x080b, 0x1008, 0x2008,
     484                 :   0x0009, 0x0904, 0x1009, 0x2009, 0x000a, 0x0905, 0x100a, 0x200a,
     485                 :   0x000b, 0x0906, 0x100b, 0x200b, 0x000c, 0x0907, 0x100c, 0x200c,
     486                 :   0x000d, 0x0908, 0x100d, 0x200d, 0x000e, 0x0909, 0x100e, 0x200e,
     487                 :   0x000f, 0x090a, 0x100f, 0x200f, 0x0010, 0x090b, 0x1010, 0x2010,
     488                 :   0x0011, 0x0a04, 0x1011, 0x2011, 0x0012, 0x0a05, 0x1012, 0x2012,
     489                 :   0x0013, 0x0a06, 0x1013, 0x2013, 0x0014, 0x0a07, 0x1014, 0x2014,
     490                 :   0x0015, 0x0a08, 0x1015, 0x2015, 0x0016, 0x0a09, 0x1016, 0x2016,
     491                 :   0x0017, 0x0a0a, 0x1017, 0x2017, 0x0018, 0x0a0b, 0x1018, 0x2018,
     492                 :   0x0019, 0x0b04, 0x1019, 0x2019, 0x001a, 0x0b05, 0x101a, 0x201a,
     493                 :   0x001b, 0x0b06, 0x101b, 0x201b, 0x001c, 0x0b07, 0x101c, 0x201c,
     494                 :   0x001d, 0x0b08, 0x101d, 0x201d, 0x001e, 0x0b09, 0x101e, 0x201e,
     495                 :   0x001f, 0x0b0a, 0x101f, 0x201f, 0x0020, 0x0b0b, 0x1020, 0x2020,
     496                 :   0x0021, 0x0c04, 0x1021, 0x2021, 0x0022, 0x0c05, 0x1022, 0x2022,
     497                 :   0x0023, 0x0c06, 0x1023, 0x2023, 0x0024, 0x0c07, 0x1024, 0x2024,
     498                 :   0x0025, 0x0c08, 0x1025, 0x2025, 0x0026, 0x0c09, 0x1026, 0x2026,
     499                 :   0x0027, 0x0c0a, 0x1027, 0x2027, 0x0028, 0x0c0b, 0x1028, 0x2028,
     500                 :   0x0029, 0x0d04, 0x1029, 0x2029, 0x002a, 0x0d05, 0x102a, 0x202a,
     501                 :   0x002b, 0x0d06, 0x102b, 0x202b, 0x002c, 0x0d07, 0x102c, 0x202c,
     502                 :   0x002d, 0x0d08, 0x102d, 0x202d, 0x002e, 0x0d09, 0x102e, 0x202e,
     503                 :   0x002f, 0x0d0a, 0x102f, 0x202f, 0x0030, 0x0d0b, 0x1030, 0x2030,
     504                 :   0x0031, 0x0e04, 0x1031, 0x2031, 0x0032, 0x0e05, 0x1032, 0x2032,
     505                 :   0x0033, 0x0e06, 0x1033, 0x2033, 0x0034, 0x0e07, 0x1034, 0x2034,
     506                 :   0x0035, 0x0e08, 0x1035, 0x2035, 0x0036, 0x0e09, 0x1036, 0x2036,
     507                 :   0x0037, 0x0e0a, 0x1037, 0x2037, 0x0038, 0x0e0b, 0x1038, 0x2038,
     508                 :   0x0039, 0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a,
     509                 :   0x003b, 0x0f06, 0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c,
     510                 :   0x0801, 0x0f08, 0x103d, 0x203d, 0x1001, 0x0f09, 0x103e, 0x203e,
     511                 :   0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040
     512                 : };
     513                 : 
     514                 : // In debug mode, allow optional computation of the table at startup.
     515                 : // Also, check that the decompression table is correct.
     516                 : #ifndef NDEBUG
     517                 : DEFINE_bool(snappy_dump_decompression_table, false,
     518                 :             "If true, we print the decompression table at startup.");
     519                 : 
     520               0 : static uint16 MakeEntry(unsigned int extra,
     521                 :                         unsigned int len,
     522                 :                         unsigned int copy_offset) {
     523                 :   // Check that all of the fields fit within the allocated space
     524               0 :   DCHECK_EQ(extra,       extra & 0x7);          // At most 3 bits
     525               0 :   DCHECK_EQ(copy_offset, copy_offset & 0x7);    // At most 3 bits
     526               0 :   DCHECK_EQ(len,         len & 0x7f);           // At most 7 bits
     527               0 :   return len | (copy_offset << 8) | (extra << 11);
     528                 : }
     529                 : 
     530               0 : static void ComputeTable() {
     531                 :   uint16 dst[256];
     532                 : 
     533                 :   // Place invalid entries in all places to detect missing initialization
     534               0 :   int assigned = 0;
     535               0 :   for (int i = 0; i < 256; i++) {
     536               0 :     dst[i] = 0xffff;
     537                 :   }
     538                 : 
     539                 :   // Small LITERAL entries.  We store (len-1) in the top 6 bits.
     540               0 :   for (unsigned int len = 1; len <= 60; len++) {
     541               0 :     dst[LITERAL | ((len-1) << 2)] = MakeEntry(0, len, 0);
     542               0 :     assigned++;
     543                 :   }
     544                 : 
     545                 :   // Large LITERAL entries.  We use 60..63 in the high 6 bits to
     546                 :   // encode the number of bytes of length info that follow the opcode.
     547               0 :   for (unsigned int extra_bytes = 1; extra_bytes <= 4; extra_bytes++) {
     548                 :     // We set the length field in the lookup table to 1 because extra
     549                 :     // bytes encode len-1.
     550               0 :     dst[LITERAL | ((extra_bytes+59) << 2)] = MakeEntry(extra_bytes, 1, 0);
     551               0 :     assigned++;
     552                 :   }
     553                 : 
     554                 :   // COPY_1_BYTE_OFFSET.
     555                 :   //
     556                 :   // The tag byte in the compressed data stores len-4 in 3 bits, and
     557                 :   // offset/256 in 5 bits.  offset%256 is stored in the next byte.
     558                 :   //
     559                 :   // This format is used for length in range [4..11] and offset in
     560                 :   // range [0..2047]
     561               0 :   for (unsigned int len = 4; len < 12; len++) {
     562               0 :     for (unsigned int offset = 0; offset < 2048; offset += 256) {
     563               0 :       dst[COPY_1_BYTE_OFFSET | ((len-4)<<2) | ((offset>>8)<<5)] =
     564               0 :         MakeEntry(1, len, offset>>8);
     565               0 :       assigned++;
     566                 :     }
     567                 :   }
     568                 : 
     569                 :   // COPY_2_BYTE_OFFSET.
     570                 :   // Tag contains len-1 in top 6 bits, and offset in next two bytes.
     571               0 :   for (unsigned int len = 1; len <= 64; len++) {
     572               0 :     dst[COPY_2_BYTE_OFFSET | ((len-1)<<2)] = MakeEntry(2, len, 0);
     573               0 :     assigned++;
     574                 :   }
     575                 : 
     576                 :   // COPY_4_BYTE_OFFSET.
     577                 :   // Tag contents len-1 in top 6 bits, and offset in next four bytes.
     578               0 :   for (unsigned int len = 1; len <= 64; len++) {
     579               0 :     dst[COPY_4_BYTE_OFFSET | ((len-1)<<2)] = MakeEntry(4, len, 0);
     580               0 :     assigned++;
     581                 :   }
     582                 : 
     583                 :   // Check that each entry was initialized exactly once.
     584               0 :   CHECK_EQ(assigned, 256);
     585               0 :   for (int i = 0; i < 256; i++) {
     586               0 :     CHECK_NE(dst[i], 0xffff);
     587                 :   }
     588                 : 
     589               0 :   if (FLAGS_snappy_dump_decompression_table) {
     590               0 :     printf("static const uint16 char_table[256] = {\n  ");
     591               0 :     for (int i = 0; i < 256; i++) {
     592                 :       printf("0x%04x%s",
     593               0 :              dst[i],
     594               0 :              ((i == 255) ? "\n" : (((i%8) == 7) ? ",\n  " : ", ")));
     595                 :     }
     596               0 :     printf("};\n");
     597                 :   }
     598                 : 
     599                 :   // Check that computed table matched recorded table
     600               0 :   for (int i = 0; i < 256; i++) {
     601               0 :     CHECK_EQ(dst[i], char_table[i]);
     602                 :   }
     603               0 : }
     604                 : #endif /* !NDEBUG */
     605                 : 
     606                 : // Helper class for decompression
     607                 : class SnappyDecompressor {
     608                 :  private:
     609                 :   Source*       reader_;         // Underlying source of bytes to decompress
     610                 :   const char*   ip_;             // Points to next buffered byte
     611                 :   const char*   ip_limit_;       // Points just past buffered bytes
     612                 :   uint32        peeked_;         // Bytes peeked from reader (need to skip)
     613                 :   bool          eof_;            // Hit end of input without an error?
     614                 :   char          scratch_[5];     // Temporary buffer for PeekFast() boundaries
     615                 : 
     616                 :   // Ensure that all of the tag metadata for the next tag is available
     617                 :   // in [ip_..ip_limit_-1].  Also ensures that [ip,ip+4] is readable even
     618                 :   // if (ip_limit_ - ip_ < 5).
     619                 :   //
     620                 :   // Returns true on success, false on error or end of input.
     621                 :   bool RefillTag();
     622                 : 
     623                 :  public:
     624            1970 :   explicit SnappyDecompressor(Source* reader)
     625                 :       : reader_(reader),
     626                 :         ip_(NULL),
     627                 :         ip_limit_(NULL),
     628                 :         peeked_(0),
     629            1970 :         eof_(false) {
     630            1970 :   }
     631                 : 
     632            1970 :   ~SnappyDecompressor() {
     633                 :     // Advance past any bytes we peeked at from the reader
     634            1970 :     reader_->Skip(peeked_);
     635            1970 :   }
     636                 : 
     637                 :   // Returns true iff we have hit the end of the input without an error.
     638            1970 :   bool eof() const {
     639            1970 :     return eof_;
     640                 :   }
     641                 : 
     642                 :   // Read the uncompressed length stored at the start of the compressed data.
     643                 :   // On succcess, stores the length in *result and returns true.
     644                 :   // On failure, returns false.
     645            1970 :   bool ReadUncompressedLength(uint32* result) {
     646            1970 :     DCHECK(ip_ == NULL);       // Must not have read anything yet
     647                 :     // Length is encoded in 1..5 bytes
     648            1970 :     *result = 0;
     649            1970 :     uint32 shift = 0;
     650             224 :     while (true) {
     651            2194 :       if (shift >= 32) return false;
     652                 :       size_t n;
     653            2194 :       const char* ip = reader_->Peek(&n);
     654            2194 :       if (n == 0) return false;
     655            2194 :       const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
     656            2194 :       reader_->Skip(1);
     657            2194 :       *result |= static_cast<uint32>(c & 0x7f) << shift;
     658            2194 :       if (c < 128) {
     659                 :         break;
     660                 :       }
     661             224 :       shift += 7;
     662                 :     }
     663            1970 :     return true;
     664                 :   }
     665                 : 
     666                 :   // Process the next item found in the input.
     667                 :   // Returns true if successful, false on error or end of input.
     668                 :   template <class Writer>
     669            1970 :   void DecompressAllTags(Writer* writer) {
     670            1970 :     const char* ip = ip_;
     671                 : 
     672                 :     // We could have put this refill fragment only at the beginning of the loop.
     673                 :     // However, duplicating it at the end of each branch gives the compiler more
     674                 :     // scope to optimize the <ip_limit_ - ip> expression based on the local
     675                 :     // context, which overall increases speed.
     676                 :     #define MAYBE_REFILL() \
     677                 :         if (ip_limit_ - ip < 5) { \
     678                 :           ip_ = ip; \
     679                 :           if (!RefillTag()) return; \
     680                 :           ip = ip_; \
     681                 :         }
     682                 : 
     683            1970 :     MAYBE_REFILL();
     684            7461 :     for ( ;; ) {
     685            9431 :       const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip++));
     686                 : 
     687            9431 :       if ((c & 0x3) == LITERAL) {
     688            5181 :         size_t literal_length = (c >> 2) + 1u;
     689            5181 :         if (writer->TryFastAppend(ip, ip_limit_ - ip, literal_length)) {
     690            3845 :           DCHECK_LT(literal_length, 61);
     691            3845 :           ip += literal_length;
     692            3845 :           MAYBE_REFILL();
     693            2619 :           continue;
     694                 :         }
     695            1336 :         if (PREDICT_FALSE(literal_length >= 61)) {
     696                 :           // Long literal.
     697               0 :           const size_t literal_length_length = literal_length - 60;
     698               0 :           literal_length =
     699                 :               (LittleEndian::Load32(ip) & wordmask[literal_length_length]) + 1;
     700               0 :           ip += literal_length_length;
     701                 :         }
     702                 : 
     703            1336 :         size_t avail = ip_limit_ - ip;
     704            2672 :         while (avail < literal_length) {
     705               0 :           if (!writer->Append(ip, avail)) return;
     706               0 :           literal_length -= avail;
     707               0 :           reader_->Skip(peeked_);
     708                 :           size_t n;
     709               0 :           ip = reader_->Peek(&n);
     710               0 :           avail = n;
     711               0 :           peeked_ = avail;
     712               0 :           if (avail == 0) return;  // Premature end of input
     713               0 :           ip_limit_ = ip + avail;
     714                 :         }
     715            1336 :         if (!writer->Append(ip, literal_length)) {
     716               0 :           return;
     717                 :         }
     718            1336 :         ip += literal_length;
     719            1336 :         MAYBE_REFILL();
     720                 :       } else {
     721            4250 :         const uint32 entry = char_table[c];
     722            4250 :         const uint32 trailer = LittleEndian::Load32(ip) & wordmask[entry >> 11];
     723            4250 :         const uint32 length = entry & 0xff;
     724            4250 :         ip += entry >> 11;
     725                 : 
     726                 :         // copy_offset/256 is encoded in bits 8..10.  By just fetching
     727                 :         // those bits, we get copy_offset (since the bit-field starts at
     728                 :         // bit 8).
     729            4250 :         const uint32 copy_offset = entry & 0x700;
     730            4250 :         if (!writer->AppendFromSelf(copy_offset + trailer, length)) {
     731               0 :           return;
     732                 :         }
     733            4250 :         MAYBE_REFILL();
     734                 :       }
     735                 :     }
     736                 : 
     737                 : #undef MAYBE_REFILL
     738                 :   }
     739                 : };
     740                 : 
     741            3945 : bool SnappyDecompressor::RefillTag() {
     742            3945 :   const char* ip = ip_;
     743            3945 :   if (ip == ip_limit_) {
     744                 :     // Fetch a new fragment from the reader
     745            3940 :     reader_->Skip(peeked_);   // All peeked bytes are used up
     746                 :     size_t n;
     747            3940 :     ip = reader_->Peek(&n);
     748            3940 :     peeked_ = n;
     749            3940 :     if (n == 0) {
     750            1970 :       eof_ = true;
     751            1970 :       return false;
     752                 :     }
     753            1970 :     ip_limit_ = ip + n;
     754                 :   }
     755                 : 
     756                 :   // Read the tag character
     757            1975 :   DCHECK_LT(ip, ip_limit_);
     758            1975 :   const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
     759            1975 :   const uint32 entry = char_table[c];
     760            1975 :   const uint32 needed = (entry >> 11) + 1;  // +1 byte for 'c'
     761            1975 :   DCHECK_LE(needed, sizeof(scratch_));
     762                 : 
     763                 :   // Read more bytes from reader if needed
     764            1975 :   uint32 nbuf = ip_limit_ - ip;
     765            1975 :   if (nbuf < needed) {
     766                 :     // Stitch together bytes from ip and reader to form the word
     767                 :     // contents.  We store the needed bytes in "scratch_".  They
     768                 :     // will be consumed immediately by the caller since we do not
     769                 :     // read more than we need.
     770               0 :     memmove(scratch_, ip, nbuf);
     771               0 :     reader_->Skip(peeked_);  // All peeked bytes are used up
     772               0 :     peeked_ = 0;
     773               0 :     while (nbuf < needed) {
     774                 :       size_t length;
     775               0 :       const char* src = reader_->Peek(&length);
     776               0 :       if (length == 0) return false;
     777               0 :       uint32 to_add = min<uint32>(needed - nbuf, length);
     778               0 :       memcpy(scratch_ + nbuf, src, to_add);
     779               0 :       nbuf += to_add;
     780               0 :       reader_->Skip(to_add);
     781                 :     }
     782               0 :     DCHECK_EQ(nbuf, needed);
     783               0 :     ip_ = scratch_;
     784               0 :     ip_limit_ = scratch_ + needed;
     785            1975 :   } else if (nbuf < 5) {
     786                 :     // Have enough bytes, but move into scratch_ so that we do not
     787                 :     // read past end of input
     788               5 :     memmove(scratch_, ip, nbuf);
     789               5 :     reader_->Skip(peeked_);  // All peeked bytes are used up
     790               5 :     peeked_ = 0;
     791               5 :     ip_ = scratch_;
     792               5 :     ip_limit_ = scratch_ + nbuf;
     793                 :   } else {
     794                 :     // Pass pointer to buffer returned by reader_.
     795            1970 :     ip_ = ip;
     796                 :   }
     797            1975 :   return true;
     798                 : }
     799                 : 
     800                 : template <typename Writer>
     801            1970 : static bool InternalUncompress(Source* r,
     802                 :                                Writer* writer,
     803                 :                                uint32 max_len) {
     804                 :   // Read the uncompressed length from the front of the compressed input
     805            3940 :   SnappyDecompressor decompressor(r);
     806            1970 :   uint32 uncompressed_len = 0;
     807            1970 :   if (!decompressor.ReadUncompressedLength(&uncompressed_len)) return false;
     808                 :   // Protect against possible DoS attack
     809            1970 :   if (static_cast<uint64>(uncompressed_len) > max_len) {
     810               0 :     return false;
     811                 :   }
     812                 : 
     813            1970 :   writer->SetExpectedLength(uncompressed_len);
     814                 : 
     815                 :   // Process the entire input
     816            1970 :   decompressor.DecompressAllTags(writer);
     817            1970 :   return (decompressor.eof() && writer->CheckLength());
     818                 : }
     819                 : 
     820               0 : bool GetUncompressedLength(Source* source, uint32* result) {
     821               0 :   SnappyDecompressor decompressor(source);
     822               0 :   return decompressor.ReadUncompressedLength(result);
     823                 : }
     824                 : 
     825            1837 : size_t Compress(Source* reader, Sink* writer) {
     826            1837 :   size_t written = 0;
     827            1837 :   size_t N = reader->Available();
     828                 :   char ulength[Varint::kMax32];
     829            1837 :   char* p = Varint::Encode32(ulength, N);
     830            1837 :   writer->Append(ulength, p-ulength);
     831            1837 :   written += (p - ulength);
     832                 : 
     833            3674 :   internal::WorkingMemory wmem;
     834            1837 :   char* scratch = NULL;
     835            1837 :   char* scratch_output = NULL;
     836                 : 
     837            5511 :   while (N > 0) {
     838                 :     // Get next block to compress (without copying if possible)
     839                 :     size_t fragment_size;
     840            1837 :     const char* fragment = reader->Peek(&fragment_size);
     841            1837 :     DCHECK_NE(fragment_size, 0) << ": premature end of input";
     842            1837 :     const size_t num_to_read = min(N, kBlockSize);
     843            1837 :     size_t bytes_read = fragment_size;
     844                 : 
     845            1837 :     size_t pending_advance = 0;
     846            1837 :     if (bytes_read >= num_to_read) {
     847                 :       // Buffer returned by reader is large enough
     848            1837 :       pending_advance = num_to_read;
     849            1837 :       fragment_size = num_to_read;
     850                 :     } else {
     851                 :       // Read into scratch buffer
     852               0 :       if (scratch == NULL) {
     853                 :         // If this is the last iteration, we want to allocate N bytes
     854                 :         // of space, otherwise the max possible kBlockSize space.
     855                 :         // num_to_read contains exactly the correct value
     856               0 :         scratch = new char[num_to_read];
     857                 :       }
     858               0 :       memcpy(scratch, fragment, bytes_read);
     859               0 :       reader->Skip(bytes_read);
     860                 : 
     861               0 :       while (bytes_read < num_to_read) {
     862               0 :         fragment = reader->Peek(&fragment_size);
     863               0 :         size_t n = min<size_t>(fragment_size, num_to_read - bytes_read);
     864               0 :         memcpy(scratch + bytes_read, fragment, n);
     865               0 :         bytes_read += n;
     866               0 :         reader->Skip(n);
     867                 :       }
     868               0 :       DCHECK_EQ(bytes_read, num_to_read);
     869               0 :       fragment = scratch;
     870               0 :       fragment_size = num_to_read;
     871                 :     }
     872            1837 :     DCHECK_EQ(fragment_size, num_to_read);
     873                 : 
     874                 :     // Get encoding table for compression
     875                 :     int table_size;
     876            1837 :     uint16* table = wmem.GetHashTable(num_to_read, &table_size);
     877                 : 
     878                 :     // Compress input_fragment and append to dest
     879            1837 :     const int max_output = MaxCompressedLength(num_to_read);
     880                 : 
     881                 :     // Need a scratch buffer for the output, in case the byte sink doesn't
     882                 :     // have room for us directly.
     883            1837 :     if (scratch_output == NULL) {
     884            3674 :       scratch_output = new char[max_output];
     885                 :     } else {
     886                 :       // Since we encode kBlockSize regions followed by a region
     887                 :       // which is <= kBlockSize in length, a previously allocated
     888                 :       // scratch_output[] region is big enough for this iteration.
     889                 :     }
     890            1837 :     char* dest = writer->GetAppendBuffer(max_output, scratch_output);
     891                 :     char* end = internal::CompressFragment(fragment, fragment_size,
     892            1837 :                                            dest, table, table_size);
     893            1837 :     writer->Append(dest, end - dest);
     894            1837 :     written += (end - dest);
     895                 : 
     896            1837 :     N -= num_to_read;
     897            1837 :     reader->Skip(pending_advance);
     898                 :   }
     899                 : 
     900            1837 :   delete[] scratch;
     901            1837 :   delete[] scratch_output;
     902                 : 
     903            1837 :   return written;
     904                 : }
     905                 : 
     906                 : // -----------------------------------------------------------------------
     907                 : // Flat array interfaces
     908                 : // -----------------------------------------------------------------------
     909                 : 
     910                 : // A type that writes to a flat array.
     911                 : // Note that this is not a "ByteSink", but a type that matches the
     912                 : // Writer template argument to SnappyDecompressor::DecompressAllTags().
     913                 : class SnappyArrayWriter {
     914                 :  private:
     915                 :   char* base_;
     916                 :   char* op_;
     917                 :   char* op_limit_;
     918                 : 
     919                 :  public:
     920            1970 :   inline explicit SnappyArrayWriter(char* dst)
     921                 :       : base_(dst),
     922            1970 :         op_(dst) {
     923            1970 :   }
     924                 : 
     925            1970 :   inline void SetExpectedLength(size_t len) {
     926            1970 :     op_limit_ = op_ + len;
     927            1970 :   }
     928                 : 
     929            1970 :   inline bool CheckLength() const {
     930            1970 :     return op_ == op_limit_;
     931                 :   }
     932                 : 
     933            1336 :   inline bool Append(const char* ip, size_t len) {
     934            1336 :     char* op = op_;
     935            1336 :     const size_t space_left = op_limit_ - op;
     936            1336 :     if (space_left < len) {
     937               0 :       return false;
     938                 :     }
     939            1336 :     memcpy(op, ip, len);
     940            1336 :     op_ = op + len;
     941            1336 :     return true;
     942                 :   }
     943                 : 
     944            5181 :   inline bool TryFastAppend(const char* ip, size_t available, size_t len) {
     945            5181 :     char* op = op_;
     946            5181 :     const size_t space_left = op_limit_ - op;
     947            5181 :     if (len <= 16 && available >= 16 && space_left >= 16) {
     948                 :       // Fast path, used for the majority (about 95%) of invocations.
     949            3845 :       UNALIGNED_STORE64(op, UNALIGNED_LOAD64(ip));
     950            3845 :       UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(ip + 8));
     951            3845 :       op_ = op + len;
     952            3845 :       return true;
     953                 :     } else {
     954            1336 :       return false;
     955                 :     }
     956                 :   }
     957                 : 
     958            4250 :   inline bool AppendFromSelf(size_t offset, size_t len) {
     959            4250 :     char* op = op_;
     960            4250 :     const size_t space_left = op_limit_ - op;
     961                 : 
     962            4250 :     if (op - base_ <= offset - 1u) {  // -1u catches offset==0
     963               0 :       return false;
     964                 :     }
     965            4250 :     if (len <= 16 && offset >= 8 && space_left >= 16) {
     966                 :       // Fast path, used for the majority (70-80%) of dynamic invocations.
     967            3243 :       UNALIGNED_STORE64(op, UNALIGNED_LOAD64(op - offset));
     968            3243 :       UNALIGNED_STORE64(op + 8, UNALIGNED_LOAD64(op - offset + 8));
     969                 :     } else {
     970            1007 :       if (space_left >= len + kMaxIncrementCopyOverflow) {
     971             999 :         IncrementalCopyFastPath(op - offset, op, len);
     972                 :       } else {
     973               8 :         if (space_left < len) {
     974               0 :           return false;
     975                 :         }
     976               8 :         IncrementalCopy(op - offset, op, len);
     977                 :       }
     978                 :     }
     979                 : 
     980            4250 :     op_ = op + len;
     981            4250 :     return true;
     982                 :   }
     983                 : };
     984                 : 
     985            1970 : bool RawUncompress(const char* compressed, size_t n, char* uncompressed) {
     986            3940 :   ByteArraySource reader(compressed, n);
     987            1970 :   return RawUncompress(&reader, uncompressed);
     988                 : }
     989                 : 
     990            1970 : bool RawUncompress(Source* compressed, char* uncompressed) {
     991            1970 :   SnappyArrayWriter output(uncompressed);
     992            1970 :   return InternalUncompress(compressed, &output, kuint32max);
     993                 : }
     994                 : 
     995               0 : bool Uncompress(const char* compressed, size_t n, string* uncompressed) {
     996                 :   size_t ulength;
     997               0 :   if (!GetUncompressedLength(compressed, n, &ulength)) {
     998               0 :     return false;
     999                 :   }
    1000                 :   // Protect against possible DoS attack
    1001               0 :   if ((static_cast<uint64>(ulength) + uncompressed->size()) >
    1002               0 :       uncompressed->max_size()) {
    1003               0 :     return false;
    1004                 :   }
    1005               0 :   STLStringResizeUninitialized(uncompressed, ulength);
    1006               0 :   return RawUncompress(compressed, n, string_as_array(uncompressed));
    1007                 : }
    1008                 : 
    1009                 : 
    1010                 : // A Writer that drops everything on the floor and just does validation
    1011                 : class SnappyDecompressionValidator {
    1012                 :  private:
    1013                 :   size_t expected_;
    1014                 :   size_t produced_;
    1015                 : 
    1016                 :  public:
    1017               0 :   inline SnappyDecompressionValidator() : produced_(0) { }
    1018               0 :   inline void SetExpectedLength(size_t len) {
    1019               0 :     expected_ = len;
    1020               0 :   }
    1021               0 :   inline bool CheckLength() const {
    1022               0 :     return expected_ == produced_;
    1023                 :   }
    1024               0 :   inline bool Append(const char* ip, size_t len) {
    1025               0 :     produced_ += len;
    1026               0 :     return produced_ <= expected_;
    1027                 :   }
    1028               0 :   inline bool TryFastAppend(const char* ip, size_t available, size_t length) {
    1029               0 :     return false;
    1030                 :   }
    1031               0 :   inline bool AppendFromSelf(size_t offset, size_t len) {
    1032               0 :     if (produced_ <= offset - 1u) return false;  // -1u catches offset==0
    1033               0 :     produced_ += len;
    1034               0 :     return produced_ <= expected_;
    1035                 :   }
    1036                 : };
    1037                 : 
    1038               0 : bool IsValidCompressedBuffer(const char* compressed, size_t n) {
    1039               0 :   ByteArraySource reader(compressed, n);
    1040               0 :   SnappyDecompressionValidator writer;
    1041               0 :   return InternalUncompress(&reader, &writer, kuint32max);
    1042                 : }
    1043                 : 
    1044            1837 : void RawCompress(const char* input,
    1045                 :                  size_t input_length,
    1046                 :                  char* compressed,
    1047                 :                  size_t* compressed_length) {
    1048            3674 :   ByteArraySource reader(input, input_length);
    1049            3674 :   UncheckedByteArraySink writer(compressed);
    1050            1837 :   Compress(&reader, &writer);
    1051                 : 
    1052                 :   // Compute how many bytes were added
    1053            1837 :   *compressed_length = (writer.CurrentDestination() - compressed);
    1054            1837 : }
    1055                 : 
    1056               0 : size_t Compress(const char* input, size_t input_length, string* compressed) {
    1057                 :   // Pre-grow the buffer to the max length of the compressed output
    1058               0 :   compressed->resize(MaxCompressedLength(input_length));
    1059                 : 
    1060                 :   size_t compressed_length;
    1061                 :   RawCompress(input, input_length, string_as_array(compressed),
    1062               0 :               &compressed_length);
    1063               0 :   compressed->resize(compressed_length);
    1064               0 :   return compressed_length;
    1065                 : }
    1066                 : 
    1067                 : 
    1068            4392 : } // end namespace snappy
    1069                 : 

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