LCOV - code coverage report
Current view: directory - media/libjpeg - jidctfst.c (source / functions) Found Hit Coverage
Test: app.info Lines: 108 0 0.0 %
Date: 2012-06-02 Functions: 1 0 0.0 %

       1                 : /*
       2                 :  * jidctfst.c
       3                 :  *
       4                 :  * Copyright (C) 1994-1998, Thomas G. Lane.
       5                 :  * This file is part of the Independent JPEG Group's software.
       6                 :  * For conditions of distribution and use, see the accompanying README file.
       7                 :  *
       8                 :  * This file contains a fast, not so accurate integer implementation of the
       9                 :  * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
      10                 :  * must also perform dequantization of the input coefficients.
      11                 :  *
      12                 :  * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
      13                 :  * on each row (or vice versa, but it's more convenient to emit a row at
      14                 :  * a time).  Direct algorithms are also available, but they are much more
      15                 :  * complex and seem not to be any faster when reduced to code.
      16                 :  *
      17                 :  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
      18                 :  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
      19                 :  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
      20                 :  * JPEG textbook (see REFERENCES section in file README).  The following code
      21                 :  * is based directly on figure 4-8 in P&M.
      22                 :  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
      23                 :  * possible to arrange the computation so that many of the multiplies are
      24                 :  * simple scalings of the final outputs.  These multiplies can then be
      25                 :  * folded into the multiplications or divisions by the JPEG quantization
      26                 :  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
      27                 :  * to be done in the DCT itself.
      28                 :  * The primary disadvantage of this method is that with fixed-point math,
      29                 :  * accuracy is lost due to imprecise representation of the scaled
      30                 :  * quantization values.  The smaller the quantization table entry, the less
      31                 :  * precise the scaled value, so this implementation does worse with high-
      32                 :  * quality-setting files than with low-quality ones.
      33                 :  */
      34                 : 
      35                 : #define JPEG_INTERNALS
      36                 : #include "jinclude.h"
      37                 : #include "jpeglib.h"
      38                 : #include "jdct.h"             /* Private declarations for DCT subsystem */
      39                 : 
      40                 : #ifdef DCT_IFAST_SUPPORTED
      41                 : 
      42                 : 
      43                 : /*
      44                 :  * This module is specialized to the case DCTSIZE = 8.
      45                 :  */
      46                 : 
      47                 : #if DCTSIZE != 8
      48                 :   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
      49                 : #endif
      50                 : 
      51                 : 
      52                 : /* Scaling decisions are generally the same as in the LL&M algorithm;
      53                 :  * see jidctint.c for more details.  However, we choose to descale
      54                 :  * (right shift) multiplication products as soon as they are formed,
      55                 :  * rather than carrying additional fractional bits into subsequent additions.
      56                 :  * This compromises accuracy slightly, but it lets us save a few shifts.
      57                 :  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
      58                 :  * everywhere except in the multiplications proper; this saves a good deal
      59                 :  * of work on 16-bit-int machines.
      60                 :  *
      61                 :  * The dequantized coefficients are not integers because the AA&N scaling
      62                 :  * factors have been incorporated.  We represent them scaled up by PASS1_BITS,
      63                 :  * so that the first and second IDCT rounds have the same input scaling.
      64                 :  * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to
      65                 :  * avoid a descaling shift; this compromises accuracy rather drastically
      66                 :  * for small quantization table entries, but it saves a lot of shifts.
      67                 :  * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,
      68                 :  * so we use a much larger scaling factor to preserve accuracy.
      69                 :  *
      70                 :  * A final compromise is to represent the multiplicative constants to only
      71                 :  * 8 fractional bits, rather than 13.  This saves some shifting work on some
      72                 :  * machines, and may also reduce the cost of multiplication (since there
      73                 :  * are fewer one-bits in the constants).
      74                 :  */
      75                 : 
      76                 : #if BITS_IN_JSAMPLE == 8
      77                 : #define CONST_BITS  8
      78                 : #define PASS1_BITS  2
      79                 : #else
      80                 : #define CONST_BITS  8
      81                 : #define PASS1_BITS  1           /* lose a little precision to avoid overflow */
      82                 : #endif
      83                 : 
      84                 : /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
      85                 :  * causing a lot of useless floating-point operations at run time.
      86                 :  * To get around this we use the following pre-calculated constants.
      87                 :  * If you change CONST_BITS you may want to add appropriate values.
      88                 :  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
      89                 :  */
      90                 : 
      91                 : #if CONST_BITS == 8
      92                 : #define FIX_1_082392200  ((INT32)  277)         /* FIX(1.082392200) */
      93                 : #define FIX_1_414213562  ((INT32)  362)         /* FIX(1.414213562) */
      94                 : #define FIX_1_847759065  ((INT32)  473)         /* FIX(1.847759065) */
      95                 : #define FIX_2_613125930  ((INT32)  669)         /* FIX(2.613125930) */
      96                 : #else
      97                 : #define FIX_1_082392200  FIX(1.082392200)
      98                 : #define FIX_1_414213562  FIX(1.414213562)
      99                 : #define FIX_1_847759065  FIX(1.847759065)
     100                 : #define FIX_2_613125930  FIX(2.613125930)
     101                 : #endif
     102                 : 
     103                 : 
     104                 : /* We can gain a little more speed, with a further compromise in accuracy,
     105                 :  * by omitting the addition in a descaling shift.  This yields an incorrectly
     106                 :  * rounded result half the time...
     107                 :  */
     108                 : 
     109                 : #ifndef USE_ACCURATE_ROUNDING
     110                 : #undef DESCALE
     111                 : #define DESCALE(x,n)  RIGHT_SHIFT(x, n)
     112                 : #endif
     113                 : 
     114                 : 
     115                 : /* Multiply a DCTELEM variable by an INT32 constant, and immediately
     116                 :  * descale to yield a DCTELEM result.
     117                 :  */
     118                 : 
     119                 : #define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
     120                 : 
     121                 : 
     122                 : /* Dequantize a coefficient by multiplying it by the multiplier-table
     123                 :  * entry; produce a DCTELEM result.  For 8-bit data a 16x16->16
     124                 :  * multiplication will do.  For 12-bit data, the multiplier table is
     125                 :  * declared INT32, so a 32-bit multiply will be used.
     126                 :  */
     127                 : 
     128                 : #if BITS_IN_JSAMPLE == 8
     129                 : #define DEQUANTIZE(coef,quantval)  (((IFAST_MULT_TYPE) (coef)) * (quantval))
     130                 : #else
     131                 : #define DEQUANTIZE(coef,quantval)  \
     132                 :         DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS)
     133                 : #endif
     134                 : 
     135                 : 
     136                 : /* Like DESCALE, but applies to a DCTELEM and produces an int.
     137                 :  * We assume that int right shift is unsigned if INT32 right shift is.
     138                 :  */
     139                 : 
     140                 : #ifdef RIGHT_SHIFT_IS_UNSIGNED
     141                 : #define ISHIFT_TEMPS    DCTELEM ishift_temp;
     142                 : #if BITS_IN_JSAMPLE == 8
     143                 : #define DCTELEMBITS  16         /* DCTELEM may be 16 or 32 bits */
     144                 : #else
     145                 : #define DCTELEMBITS  32         /* DCTELEM must be 32 bits */
     146                 : #endif
     147                 : #define IRIGHT_SHIFT(x,shft)  \
     148                 :     ((ishift_temp = (x)) < 0 ? \
     149                 :      (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \
     150                 :      (ishift_temp >> (shft)))
     151                 : #else
     152                 : #define ISHIFT_TEMPS
     153                 : #define IRIGHT_SHIFT(x,shft)    ((x) >> (shft))
     154                 : #endif
     155                 : 
     156                 : #ifdef USE_ACCURATE_ROUNDING
     157                 : #define IDESCALE(x,n)  ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
     158                 : #else
     159                 : #define IDESCALE(x,n)  ((int) IRIGHT_SHIFT(x, n))
     160                 : #endif
     161                 : 
     162                 : 
     163                 : /*
     164                 :  * Perform dequantization and inverse DCT on one block of coefficients.
     165                 :  */
     166                 : 
     167                 : GLOBAL(void)
     168               0 : jpeg_idct_ifast (j_decompress_ptr cinfo, jpeg_component_info * compptr,
     169                 :                  JCOEFPTR coef_block,
     170                 :                  JSAMPARRAY output_buf, JDIMENSION output_col)
     171                 : {
     172                 :   DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
     173                 :   DCTELEM tmp10, tmp11, tmp12, tmp13;
     174                 :   DCTELEM z5, z10, z11, z12, z13;
     175                 :   JCOEFPTR inptr;
     176                 :   IFAST_MULT_TYPE * quantptr;
     177                 :   int * wsptr;
     178                 :   JSAMPROW outptr;
     179               0 :   JSAMPLE *range_limit = IDCT_range_limit(cinfo);
     180                 :   int ctr;
     181                 :   int workspace[DCTSIZE2];      /* buffers data between passes */
     182                 :   SHIFT_TEMPS                   /* for DESCALE */
     183                 :   ISHIFT_TEMPS                  /* for IDESCALE */
     184                 : 
     185                 :   /* Pass 1: process columns from input, store into work array. */
     186                 : 
     187               0 :   inptr = coef_block;
     188               0 :   quantptr = (IFAST_MULT_TYPE *) compptr->dct_table;
     189               0 :   wsptr = workspace;
     190               0 :   for (ctr = DCTSIZE; ctr > 0; ctr--) {
     191                 :     /* Due to quantization, we will usually find that many of the input
     192                 :      * coefficients are zero, especially the AC terms.  We can exploit this
     193                 :      * by short-circuiting the IDCT calculation for any column in which all
     194                 :      * the AC terms are zero.  In that case each output is equal to the
     195                 :      * DC coefficient (with scale factor as needed).
     196                 :      * With typical images and quantization tables, half or more of the
     197                 :      * column DCT calculations can be simplified this way.
     198                 :      */
     199                 :     
     200               0 :     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
     201               0 :         inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
     202               0 :         inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
     203               0 :         inptr[DCTSIZE*7] == 0) {
     204                 :       /* AC terms all zero */
     205               0 :       int dcval = (int) DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
     206                 : 
     207               0 :       wsptr[DCTSIZE*0] = dcval;
     208               0 :       wsptr[DCTSIZE*1] = dcval;
     209               0 :       wsptr[DCTSIZE*2] = dcval;
     210               0 :       wsptr[DCTSIZE*3] = dcval;
     211               0 :       wsptr[DCTSIZE*4] = dcval;
     212               0 :       wsptr[DCTSIZE*5] = dcval;
     213               0 :       wsptr[DCTSIZE*6] = dcval;
     214               0 :       wsptr[DCTSIZE*7] = dcval;
     215                 :       
     216               0 :       inptr++;                  /* advance pointers to next column */
     217               0 :       quantptr++;
     218               0 :       wsptr++;
     219               0 :       continue;
     220                 :     }
     221                 :     
     222                 :     /* Even part */
     223                 : 
     224               0 :     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
     225               0 :     tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
     226               0 :     tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
     227               0 :     tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
     228                 : 
     229               0 :     tmp10 = tmp0 + tmp2;        /* phase 3 */
     230               0 :     tmp11 = tmp0 - tmp2;
     231                 : 
     232               0 :     tmp13 = tmp1 + tmp3;        /* phases 5-3 */
     233               0 :     tmp12 = MULTIPLY(tmp1 - tmp3, FIX_1_414213562) - tmp13; /* 2*c4 */
     234                 : 
     235               0 :     tmp0 = tmp10 + tmp13;       /* phase 2 */
     236               0 :     tmp3 = tmp10 - tmp13;
     237               0 :     tmp1 = tmp11 + tmp12;
     238               0 :     tmp2 = tmp11 - tmp12;
     239                 :     
     240                 :     /* Odd part */
     241                 : 
     242               0 :     tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
     243               0 :     tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
     244               0 :     tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
     245               0 :     tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
     246                 : 
     247               0 :     z13 = tmp6 + tmp5;          /* phase 6 */
     248               0 :     z10 = tmp6 - tmp5;
     249               0 :     z11 = tmp4 + tmp7;
     250               0 :     z12 = tmp4 - tmp7;
     251                 : 
     252               0 :     tmp7 = z11 + z13;           /* phase 5 */
     253               0 :     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
     254                 : 
     255               0 :     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
     256               0 :     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
     257               0 :     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
     258                 : 
     259               0 :     tmp6 = tmp12 - tmp7;        /* phase 2 */
     260               0 :     tmp5 = tmp11 - tmp6;
     261               0 :     tmp4 = tmp10 + tmp5;
     262                 : 
     263               0 :     wsptr[DCTSIZE*0] = (int) (tmp0 + tmp7);
     264               0 :     wsptr[DCTSIZE*7] = (int) (tmp0 - tmp7);
     265               0 :     wsptr[DCTSIZE*1] = (int) (tmp1 + tmp6);
     266               0 :     wsptr[DCTSIZE*6] = (int) (tmp1 - tmp6);
     267               0 :     wsptr[DCTSIZE*2] = (int) (tmp2 + tmp5);
     268               0 :     wsptr[DCTSIZE*5] = (int) (tmp2 - tmp5);
     269               0 :     wsptr[DCTSIZE*4] = (int) (tmp3 + tmp4);
     270               0 :     wsptr[DCTSIZE*3] = (int) (tmp3 - tmp4);
     271                 : 
     272               0 :     inptr++;                    /* advance pointers to next column */
     273               0 :     quantptr++;
     274               0 :     wsptr++;
     275                 :   }
     276                 :   
     277                 :   /* Pass 2: process rows from work array, store into output array. */
     278                 :   /* Note that we must descale the results by a factor of 8 == 2**3, */
     279                 :   /* and also undo the PASS1_BITS scaling. */
     280                 : 
     281               0 :   wsptr = workspace;
     282               0 :   for (ctr = 0; ctr < DCTSIZE; ctr++) {
     283               0 :     outptr = output_buf[ctr] + output_col;
     284                 :     /* Rows of zeroes can be exploited in the same way as we did with columns.
     285                 :      * However, the column calculation has created many nonzero AC terms, so
     286                 :      * the simplification applies less often (typically 5% to 10% of the time).
     287                 :      * On machines with very fast multiplication, it's possible that the
     288                 :      * test takes more time than it's worth.  In that case this section
     289                 :      * may be commented out.
     290                 :      */
     291                 :     
     292                 : #ifndef NO_ZERO_ROW_TEST
     293               0 :     if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
     294               0 :         wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
     295                 :       /* AC terms all zero */
     296               0 :       JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3)
     297                 :                                   & RANGE_MASK];
     298                 :       
     299               0 :       outptr[0] = dcval;
     300               0 :       outptr[1] = dcval;
     301               0 :       outptr[2] = dcval;
     302               0 :       outptr[3] = dcval;
     303               0 :       outptr[4] = dcval;
     304               0 :       outptr[5] = dcval;
     305               0 :       outptr[6] = dcval;
     306               0 :       outptr[7] = dcval;
     307                 : 
     308               0 :       wsptr += DCTSIZE;         /* advance pointer to next row */
     309               0 :       continue;
     310                 :     }
     311                 : #endif
     312                 :     
     313                 :     /* Even part */
     314                 : 
     315               0 :     tmp10 = ((DCTELEM) wsptr[0] + (DCTELEM) wsptr[4]);
     316               0 :     tmp11 = ((DCTELEM) wsptr[0] - (DCTELEM) wsptr[4]);
     317                 : 
     318               0 :     tmp13 = ((DCTELEM) wsptr[2] + (DCTELEM) wsptr[6]);
     319               0 :     tmp12 = MULTIPLY((DCTELEM) wsptr[2] - (DCTELEM) wsptr[6], FIX_1_414213562)
     320                 :             - tmp13;
     321                 : 
     322               0 :     tmp0 = tmp10 + tmp13;
     323               0 :     tmp3 = tmp10 - tmp13;
     324               0 :     tmp1 = tmp11 + tmp12;
     325               0 :     tmp2 = tmp11 - tmp12;
     326                 : 
     327                 :     /* Odd part */
     328                 : 
     329               0 :     z13 = (DCTELEM) wsptr[5] + (DCTELEM) wsptr[3];
     330               0 :     z10 = (DCTELEM) wsptr[5] - (DCTELEM) wsptr[3];
     331               0 :     z11 = (DCTELEM) wsptr[1] + (DCTELEM) wsptr[7];
     332               0 :     z12 = (DCTELEM) wsptr[1] - (DCTELEM) wsptr[7];
     333                 : 
     334               0 :     tmp7 = z11 + z13;           /* phase 5 */
     335               0 :     tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
     336                 : 
     337               0 :     z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
     338               0 :     tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
     339               0 :     tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
     340                 : 
     341               0 :     tmp6 = tmp12 - tmp7;        /* phase 2 */
     342               0 :     tmp5 = tmp11 - tmp6;
     343               0 :     tmp4 = tmp10 + tmp5;
     344                 : 
     345                 :     /* Final output stage: scale down by a factor of 8 and range-limit */
     346                 : 
     347               0 :     outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3)
     348                 :                             & RANGE_MASK];
     349               0 :     outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3)
     350                 :                             & RANGE_MASK];
     351               0 :     outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3)
     352                 :                             & RANGE_MASK];
     353               0 :     outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3)
     354                 :                             & RANGE_MASK];
     355               0 :     outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3)
     356                 :                             & RANGE_MASK];
     357               0 :     outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3)
     358                 :                             & RANGE_MASK];
     359               0 :     outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3)
     360                 :                             & RANGE_MASK];
     361               0 :     outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3)
     362                 :                             & RANGE_MASK];
     363                 : 
     364               0 :     wsptr += DCTSIZE;           /* advance pointer to next row */
     365                 :   }
     366               0 : }
     367                 : 
     368                 : #endif /* DCT_IFAST_SUPPORTED */

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