LCOV - code coverage report
Current view: directory - modules/zlib/src - crc32.c (source / functions) Found Hit Coverage
Test: app.info Lines: 87 24 27.6 %
Date: 2012-06-02 Functions: 9 2 22.2 %

       1                 : /* crc32.c -- compute the CRC-32 of a data stream
       2                 :  * Copyright (C) 1995-2006, 2010 Mark Adler
       3                 :  * For conditions of distribution and use, see copyright notice in zlib.h
       4                 :  *
       5                 :  * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
       6                 :  * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
       7                 :  * tables for updating the shift register in one step with three exclusive-ors
       8                 :  * instead of four steps with four exclusive-ors.  This results in about a
       9                 :  * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
      10                 :  */
      11                 : 
      12                 : /* @(#) $Id$ */
      13                 : 
      14                 : /*
      15                 :   Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
      16                 :   protection on the static variables used to control the first-use generation
      17                 :   of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
      18                 :   first call get_crc_table() to initialize the tables before allowing more than
      19                 :   one thread to use crc32().
      20                 :  */
      21                 : 
      22                 : #ifdef MAKECRCH
      23                 : #  include <stdio.h>
      24                 : #  ifndef DYNAMIC_CRC_TABLE
      25                 : #    define DYNAMIC_CRC_TABLE
      26                 : #  endif /* !DYNAMIC_CRC_TABLE */
      27                 : #endif /* MAKECRCH */
      28                 : 
      29                 : #include "zutil.h"      /* for STDC and FAR definitions */
      30                 : 
      31                 : #define local static
      32                 : 
      33                 : /* Find a four-byte integer type for crc32_little() and crc32_big(). */
      34                 : #ifndef NOBYFOUR
      35                 : #  ifdef STDC           /* need ANSI C limits.h to determine sizes */
      36                 : #    include <limits.h>
      37                 : #    define BYFOUR
      38                 : #    if (UINT_MAX == 0xffffffffUL)
      39                 :        typedef unsigned int u4;
      40                 : #    else
      41                 : #      if (ULONG_MAX == 0xffffffffUL)
      42                 :          typedef unsigned long u4;
      43                 : #      else
      44                 : #        if (USHRT_MAX == 0xffffffffUL)
      45                 :            typedef unsigned short u4;
      46                 : #        else
      47                 : #          undef BYFOUR     /* can't find a four-byte integer type! */
      48                 : #        endif
      49                 : #      endif
      50                 : #    endif
      51                 : #  endif /* STDC */
      52                 : #endif /* !NOBYFOUR */
      53                 : 
      54                 : /* Definitions for doing the crc four data bytes at a time. */
      55                 : #ifdef BYFOUR
      56                 : #  define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \
      57                 :                 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
      58                 :    local unsigned long crc32_little OF((unsigned long,
      59                 :                         const unsigned char FAR *, unsigned));
      60                 :    local unsigned long crc32_big OF((unsigned long,
      61                 :                         const unsigned char FAR *, unsigned));
      62                 : #  define TBLS 8
      63                 : #else
      64                 : #  define TBLS 1
      65                 : #endif /* BYFOUR */
      66                 : 
      67                 : /* Local functions for crc concatenation */
      68                 : local unsigned long gf2_matrix_times OF((unsigned long *mat,
      69                 :                                          unsigned long vec));
      70                 : local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
      71                 : local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2);
      72                 : 
      73                 : 
      74                 : #ifdef DYNAMIC_CRC_TABLE
      75                 : 
      76                 : local volatile int crc_table_empty = 1;
      77                 : local unsigned long FAR crc_table[TBLS][256];
      78                 : local void make_crc_table OF((void));
      79                 : #ifdef MAKECRCH
      80                 :    local void write_table OF((FILE *, const unsigned long FAR *));
      81                 : #endif /* MAKECRCH */
      82                 : /*
      83                 :   Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
      84                 :   x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
      85                 : 
      86                 :   Polynomials over GF(2) are represented in binary, one bit per coefficient,
      87                 :   with the lowest powers in the most significant bit.  Then adding polynomials
      88                 :   is just exclusive-or, and multiplying a polynomial by x is a right shift by
      89                 :   one.  If we call the above polynomial p, and represent a byte as the
      90                 :   polynomial q, also with the lowest power in the most significant bit (so the
      91                 :   byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
      92                 :   where a mod b means the remainder after dividing a by b.
      93                 : 
      94                 :   This calculation is done using the shift-register method of multiplying and
      95                 :   taking the remainder.  The register is initialized to zero, and for each
      96                 :   incoming bit, x^32 is added mod p to the register if the bit is a one (where
      97                 :   x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
      98                 :   x (which is shifting right by one and adding x^32 mod p if the bit shifted
      99                 :   out is a one).  We start with the highest power (least significant bit) of
     100                 :   q and repeat for all eight bits of q.
     101                 : 
     102                 :   The first table is simply the CRC of all possible eight bit values.  This is
     103                 :   all the information needed to generate CRCs on data a byte at a time for all
     104                 :   combinations of CRC register values and incoming bytes.  The remaining tables
     105                 :   allow for word-at-a-time CRC calculation for both big-endian and little-
     106                 :   endian machines, where a word is four bytes.
     107                 : */
     108                 : local void make_crc_table()
     109                 : {
     110                 :     unsigned long c;
     111                 :     int n, k;
     112                 :     unsigned long poly;                 /* polynomial exclusive-or pattern */
     113                 :     /* terms of polynomial defining this crc (except x^32): */
     114                 :     static volatile int first = 1;      /* flag to limit concurrent making */
     115                 :     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
     116                 : 
     117                 :     /* See if another task is already doing this (not thread-safe, but better
     118                 :        than nothing -- significantly reduces duration of vulnerability in
     119                 :        case the advice about DYNAMIC_CRC_TABLE is ignored) */
     120                 :     if (first) {
     121                 :         first = 0;
     122                 : 
     123                 :         /* make exclusive-or pattern from polynomial (0xedb88320UL) */
     124                 :         poly = 0UL;
     125                 :         for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
     126                 :             poly |= 1UL << (31 - p[n]);
     127                 : 
     128                 :         /* generate a crc for every 8-bit value */
     129                 :         for (n = 0; n < 256; n++) {
     130                 :             c = (unsigned long)n;
     131                 :             for (k = 0; k < 8; k++)
     132                 :                 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
     133                 :             crc_table[0][n] = c;
     134                 :         }
     135                 : 
     136                 : #ifdef BYFOUR
     137                 :         /* generate crc for each value followed by one, two, and three zeros,
     138                 :            and then the byte reversal of those as well as the first table */
     139                 :         for (n = 0; n < 256; n++) {
     140                 :             c = crc_table[0][n];
     141                 :             crc_table[4][n] = REV(c);
     142                 :             for (k = 1; k < 4; k++) {
     143                 :                 c = crc_table[0][c & 0xff] ^ (c >> 8);
     144                 :                 crc_table[k][n] = c;
     145                 :                 crc_table[k + 4][n] = REV(c);
     146                 :             }
     147                 :         }
     148                 : #endif /* BYFOUR */
     149                 : 
     150                 :         crc_table_empty = 0;
     151                 :     }
     152                 :     else {      /* not first */
     153                 :         /* wait for the other guy to finish (not efficient, but rare) */
     154                 :         while (crc_table_empty)
     155                 :             ;
     156                 :     }
     157                 : 
     158                 : #ifdef MAKECRCH
     159                 :     /* write out CRC tables to crc32.h */
     160                 :     {
     161                 :         FILE *out;
     162                 : 
     163                 :         out = fopen("crc32.h", "w");
     164                 :         if (out == NULL) return;
     165                 :         fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
     166                 :         fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
     167                 :         fprintf(out, "local const unsigned long FAR ");
     168                 :         fprintf(out, "crc_table[TBLS][256] =\n{\n  {\n");
     169                 :         write_table(out, crc_table[0]);
     170                 : #  ifdef BYFOUR
     171                 :         fprintf(out, "#ifdef BYFOUR\n");
     172                 :         for (k = 1; k < 8; k++) {
     173                 :             fprintf(out, "  },\n  {\n");
     174                 :             write_table(out, crc_table[k]);
     175                 :         }
     176                 :         fprintf(out, "#endif\n");
     177                 : #  endif /* BYFOUR */
     178                 :         fprintf(out, "  }\n};\n");
     179                 :         fclose(out);
     180                 :     }
     181                 : #endif /* MAKECRCH */
     182                 : }
     183                 : 
     184                 : #ifdef MAKECRCH
     185                 : local void write_table(out, table)
     186                 :     FILE *out;
     187                 :     const unsigned long FAR *table;
     188                 : {
     189                 :     int n;
     190                 : 
     191                 :     for (n = 0; n < 256; n++)
     192                 :         fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : "    ", table[n],
     193                 :                 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
     194                 : }
     195                 : #endif /* MAKECRCH */
     196                 : 
     197                 : #else /* !DYNAMIC_CRC_TABLE */
     198                 : /* ========================================================================
     199                 :  * Tables of CRC-32s of all single-byte values, made by make_crc_table().
     200                 :  */
     201                 : #include "crc32.h"
     202                 : #endif /* DYNAMIC_CRC_TABLE */
     203                 : 
     204                 : /* =========================================================================
     205                 :  * This function can be used by asm versions of crc32()
     206                 :  */
     207               0 : const unsigned long FAR * ZEXPORT get_crc_table()
     208                 : {
     209                 : #ifdef DYNAMIC_CRC_TABLE
     210                 :     if (crc_table_empty)
     211                 :         make_crc_table();
     212                 : #endif /* DYNAMIC_CRC_TABLE */
     213               0 :     return (const unsigned long FAR *)crc_table;
     214                 : }
     215                 : 
     216                 : /* ========================================================================= */
     217                 : #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
     218                 : #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
     219                 : 
     220                 : /* ========================================================================= */
     221          171781 : unsigned long ZEXPORT crc32(crc, buf, len)
     222                 :     unsigned long crc;
     223                 :     const unsigned char FAR *buf;
     224                 :     uInt len;
     225                 : {
     226          171781 :     if (buf == Z_NULL) return 0UL;
     227                 : 
     228                 : #ifdef DYNAMIC_CRC_TABLE
     229                 :     if (crc_table_empty)
     230                 :         make_crc_table();
     231                 : #endif /* DYNAMIC_CRC_TABLE */
     232                 : 
     233                 : #ifdef BYFOUR
     234                 :     if (sizeof(void *) == sizeof(ptrdiff_t)) {
     235                 :         u4 endian;
     236                 : 
     237          164335 :         endian = 1;
     238          164335 :         if (*((unsigned char *)(&endian)))
     239          164335 :             return crc32_little(crc, buf, len);
     240                 :         else
     241               0 :             return crc32_big(crc, buf, len);
     242                 :     }
     243                 : #endif /* BYFOUR */
     244                 :     crc = crc ^ 0xffffffffUL;
     245                 :     while (len >= 8) {
     246                 :         DO8;
     247                 :         len -= 8;
     248                 :     }
     249                 :     if (len) do {
     250                 :         DO1;
     251                 :     } while (--len);
     252                 :     return crc ^ 0xffffffffUL;
     253                 : }
     254                 : 
     255                 : #ifdef BYFOUR
     256                 : 
     257                 : /* ========================================================================= */
     258                 : #define DOLIT4 c ^= *buf4++; \
     259                 :         c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
     260                 :             crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
     261                 : #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
     262                 : 
     263                 : /* ========================================================================= */
     264          164335 : local unsigned long crc32_little(crc, buf, len)
     265                 :     unsigned long crc;
     266                 :     const unsigned char FAR *buf;
     267                 :     unsigned len;
     268                 : {
     269                 :     register u4 c;
     270                 :     register const u4 FAR *buf4;
     271                 : 
     272          164335 :     c = (u4)crc;
     273          164335 :     c = ~c;
     274          328934 :     while (len && ((ptrdiff_t)buf & 3)) {
     275             264 :         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
     276             264 :         len--;
     277                 :     }
     278                 : 
     279          164335 :     buf4 = (const u4 FAR *)(const void FAR *)buf;
     280        20745449 :     while (len >= 32) {
     281        20416779 :         DOLIT32;
     282        20416779 :         len -= 32;
     283                 :     }
     284          352618 :     while (len >= 4) {
     285           23948 :         DOLIT4;
     286           23948 :         len -= 4;
     287                 :     }
     288          164335 :     buf = (const unsigned char FAR *)buf4;
     289                 : 
     290          164335 :     if (len) do {
     291            2691 :         c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
     292            2691 :     } while (--len);
     293          164335 :     c = ~c;
     294          164335 :     return (unsigned long)c;
     295                 : }
     296                 : 
     297                 : /* ========================================================================= */
     298                 : #define DOBIG4 c ^= *++buf4; \
     299                 :         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
     300                 :             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
     301                 : #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
     302                 : 
     303                 : /* ========================================================================= */
     304               0 : local unsigned long crc32_big(crc, buf, len)
     305                 :     unsigned long crc;
     306                 :     const unsigned char FAR *buf;
     307                 :     unsigned len;
     308                 : {
     309                 :     register u4 c;
     310                 :     register const u4 FAR *buf4;
     311                 : 
     312               0 :     c = REV((u4)crc);
     313               0 :     c = ~c;
     314               0 :     while (len && ((ptrdiff_t)buf & 3)) {
     315               0 :         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
     316               0 :         len--;
     317                 :     }
     318                 : 
     319               0 :     buf4 = (const u4 FAR *)(const void FAR *)buf;
     320               0 :     buf4--;
     321               0 :     while (len >= 32) {
     322               0 :         DOBIG32;
     323               0 :         len -= 32;
     324                 :     }
     325               0 :     while (len >= 4) {
     326               0 :         DOBIG4;
     327               0 :         len -= 4;
     328                 :     }
     329               0 :     buf4++;
     330               0 :     buf = (const unsigned char FAR *)buf4;
     331                 : 
     332               0 :     if (len) do {
     333               0 :         c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
     334               0 :     } while (--len);
     335               0 :     c = ~c;
     336               0 :     return (unsigned long)(REV(c));
     337                 : }
     338                 : 
     339                 : #endif /* BYFOUR */
     340                 : 
     341                 : #define GF2_DIM 32      /* dimension of GF(2) vectors (length of CRC) */
     342                 : 
     343                 : /* ========================================================================= */
     344               0 : local unsigned long gf2_matrix_times(mat, vec)
     345                 :     unsigned long *mat;
     346                 :     unsigned long vec;
     347                 : {
     348                 :     unsigned long sum;
     349                 : 
     350               0 :     sum = 0;
     351               0 :     while (vec) {
     352               0 :         if (vec & 1)
     353               0 :             sum ^= *mat;
     354               0 :         vec >>= 1;
     355               0 :         mat++;
     356                 :     }
     357               0 :     return sum;
     358                 : }
     359                 : 
     360                 : /* ========================================================================= */
     361               0 : local void gf2_matrix_square(square, mat)
     362                 :     unsigned long *square;
     363                 :     unsigned long *mat;
     364                 : {
     365                 :     int n;
     366                 : 
     367               0 :     for (n = 0; n < GF2_DIM; n++)
     368               0 :         square[n] = gf2_matrix_times(mat, mat[n]);
     369               0 : }
     370                 : 
     371                 : /* ========================================================================= */
     372               0 : local uLong crc32_combine_(crc1, crc2, len2)
     373                 :     uLong crc1;
     374                 :     uLong crc2;
     375                 :     z_off64_t len2;
     376                 : {
     377                 :     int n;
     378                 :     unsigned long row;
     379                 :     unsigned long even[GF2_DIM];    /* even-power-of-two zeros operator */
     380                 :     unsigned long odd[GF2_DIM];     /* odd-power-of-two zeros operator */
     381                 : 
     382                 :     /* degenerate case (also disallow negative lengths) */
     383               0 :     if (len2 <= 0)
     384               0 :         return crc1;
     385                 : 
     386                 :     /* put operator for one zero bit in odd */
     387               0 :     odd[0] = 0xedb88320UL;          /* CRC-32 polynomial */
     388               0 :     row = 1;
     389               0 :     for (n = 1; n < GF2_DIM; n++) {
     390               0 :         odd[n] = row;
     391               0 :         row <<= 1;
     392                 :     }
     393                 : 
     394                 :     /* put operator for two zero bits in even */
     395               0 :     gf2_matrix_square(even, odd);
     396                 : 
     397                 :     /* put operator for four zero bits in odd */
     398               0 :     gf2_matrix_square(odd, even);
     399                 : 
     400                 :     /* apply len2 zeros to crc1 (first square will put the operator for one
     401                 :        zero byte, eight zero bits, in even) */
     402                 :     do {
     403                 :         /* apply zeros operator for this bit of len2 */
     404               0 :         gf2_matrix_square(even, odd);
     405               0 :         if (len2 & 1)
     406               0 :             crc1 = gf2_matrix_times(even, crc1);
     407               0 :         len2 >>= 1;
     408                 : 
     409                 :         /* if no more bits set, then done */
     410               0 :         if (len2 == 0)
     411               0 :             break;
     412                 : 
     413                 :         /* another iteration of the loop with odd and even swapped */
     414               0 :         gf2_matrix_square(odd, even);
     415               0 :         if (len2 & 1)
     416               0 :             crc1 = gf2_matrix_times(odd, crc1);
     417               0 :         len2 >>= 1;
     418                 : 
     419                 :         /* if no more bits set, then done */
     420               0 :     } while (len2 != 0);
     421                 : 
     422                 :     /* return combined crc */
     423               0 :     crc1 ^= crc2;
     424               0 :     return crc1;
     425                 : }
     426                 : 
     427                 : /* ========================================================================= */
     428               0 : uLong ZEXPORT crc32_combine(crc1, crc2, len2)
     429                 :     uLong crc1;
     430                 :     uLong crc2;
     431                 :     z_off_t len2;
     432                 : {
     433               0 :     return crc32_combine_(crc1, crc2, len2);
     434                 : }
     435                 : 
     436               0 : uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
     437                 :     uLong crc1;
     438                 :     uLong crc2;
     439                 :     z_off64_t len2;
     440                 : {
     441               0 :     return crc32_combine_(crc1, crc2, len2);
     442                 : }

Generated by: LCOV version 1.7