LCOV - code coverage report
Current view: directory - media/libjpeg - jfdctfst.c (source / functions) Found Hit Coverage
Test: app.info Lines: 68 0 0.0 %
Date: 2012-06-02 Functions: 1 0 0.0 %

       1                 : /*
       2                 :  * jfdctfst.c
       3                 :  *
       4                 :  * Copyright (C) 1994-1996, 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                 :  * forward DCT (Discrete Cosine Transform).
      10                 :  *
      11                 :  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
      12                 :  * on each column.  Direct algorithms are also available, but they are
      13                 :  * much more complex and seem not to be any faster when reduced to code.
      14                 :  *
      15                 :  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
      16                 :  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
      17                 :  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
      18                 :  * JPEG textbook (see REFERENCES section in file README).  The following code
      19                 :  * is based directly on figure 4-8 in P&M.
      20                 :  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
      21                 :  * possible to arrange the computation so that many of the multiplies are
      22                 :  * simple scalings of the final outputs.  These multiplies can then be
      23                 :  * folded into the multiplications or divisions by the JPEG quantization
      24                 :  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
      25                 :  * to be done in the DCT itself.
      26                 :  * The primary disadvantage of this method is that with fixed-point math,
      27                 :  * accuracy is lost due to imprecise representation of the scaled
      28                 :  * quantization values.  The smaller the quantization table entry, the less
      29                 :  * precise the scaled value, so this implementation does worse with high-
      30                 :  * quality-setting files than with low-quality ones.
      31                 :  */
      32                 : 
      33                 : #define JPEG_INTERNALS
      34                 : #include "jinclude.h"
      35                 : #include "jpeglib.h"
      36                 : #include "jdct.h"             /* Private declarations for DCT subsystem */
      37                 : 
      38                 : #ifdef DCT_IFAST_SUPPORTED
      39                 : 
      40                 : 
      41                 : /*
      42                 :  * This module is specialized to the case DCTSIZE = 8.
      43                 :  */
      44                 : 
      45                 : #if DCTSIZE != 8
      46                 :   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
      47                 : #endif
      48                 : 
      49                 : 
      50                 : /* Scaling decisions are generally the same as in the LL&M algorithm;
      51                 :  * see jfdctint.c for more details.  However, we choose to descale
      52                 :  * (right shift) multiplication products as soon as they are formed,
      53                 :  * rather than carrying additional fractional bits into subsequent additions.
      54                 :  * This compromises accuracy slightly, but it lets us save a few shifts.
      55                 :  * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
      56                 :  * everywhere except in the multiplications proper; this saves a good deal
      57                 :  * of work on 16-bit-int machines.
      58                 :  *
      59                 :  * Again to save a few shifts, the intermediate results between pass 1 and
      60                 :  * pass 2 are not upscaled, but are represented only to integral precision.
      61                 :  *
      62                 :  * A final compromise is to represent the multiplicative constants to only
      63                 :  * 8 fractional bits, rather than 13.  This saves some shifting work on some
      64                 :  * machines, and may also reduce the cost of multiplication (since there
      65                 :  * are fewer one-bits in the constants).
      66                 :  */
      67                 : 
      68                 : #define CONST_BITS  8
      69                 : 
      70                 : 
      71                 : /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
      72                 :  * causing a lot of useless floating-point operations at run time.
      73                 :  * To get around this we use the following pre-calculated constants.
      74                 :  * If you change CONST_BITS you may want to add appropriate values.
      75                 :  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
      76                 :  */
      77                 : 
      78                 : #if CONST_BITS == 8
      79                 : #define FIX_0_382683433  ((INT32)   98)         /* FIX(0.382683433) */
      80                 : #define FIX_0_541196100  ((INT32)  139)         /* FIX(0.541196100) */
      81                 : #define FIX_0_707106781  ((INT32)  181)         /* FIX(0.707106781) */
      82                 : #define FIX_1_306562965  ((INT32)  334)         /* FIX(1.306562965) */
      83                 : #else
      84                 : #define FIX_0_382683433  FIX(0.382683433)
      85                 : #define FIX_0_541196100  FIX(0.541196100)
      86                 : #define FIX_0_707106781  FIX(0.707106781)
      87                 : #define FIX_1_306562965  FIX(1.306562965)
      88                 : #endif
      89                 : 
      90                 : 
      91                 : /* We can gain a little more speed, with a further compromise in accuracy,
      92                 :  * by omitting the addition in a descaling shift.  This yields an incorrectly
      93                 :  * rounded result half the time...
      94                 :  */
      95                 : 
      96                 : #ifndef USE_ACCURATE_ROUNDING
      97                 : #undef DESCALE
      98                 : #define DESCALE(x,n)  RIGHT_SHIFT(x, n)
      99                 : #endif
     100                 : 
     101                 : 
     102                 : /* Multiply a DCTELEM variable by an INT32 constant, and immediately
     103                 :  * descale to yield a DCTELEM result.
     104                 :  */
     105                 : 
     106                 : #define MULTIPLY(var,const)  ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
     107                 : 
     108                 : 
     109                 : /*
     110                 :  * Perform the forward DCT on one block of samples.
     111                 :  */
     112                 : 
     113                 : GLOBAL(void)
     114               0 : jpeg_fdct_ifast (DCTELEM * data)
     115                 : {
     116                 :   DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
     117                 :   DCTELEM tmp10, tmp11, tmp12, tmp13;
     118                 :   DCTELEM z1, z2, z3, z4, z5, z11, z13;
     119                 :   DCTELEM *dataptr;
     120                 :   int ctr;
     121                 :   SHIFT_TEMPS
     122                 : 
     123                 :   /* Pass 1: process rows. */
     124                 : 
     125               0 :   dataptr = data;
     126               0 :   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
     127               0 :     tmp0 = dataptr[0] + dataptr[7];
     128               0 :     tmp7 = dataptr[0] - dataptr[7];
     129               0 :     tmp1 = dataptr[1] + dataptr[6];
     130               0 :     tmp6 = dataptr[1] - dataptr[6];
     131               0 :     tmp2 = dataptr[2] + dataptr[5];
     132               0 :     tmp5 = dataptr[2] - dataptr[5];
     133               0 :     tmp3 = dataptr[3] + dataptr[4];
     134               0 :     tmp4 = dataptr[3] - dataptr[4];
     135                 :     
     136                 :     /* Even part */
     137                 :     
     138               0 :     tmp10 = tmp0 + tmp3;        /* phase 2 */
     139               0 :     tmp13 = tmp0 - tmp3;
     140               0 :     tmp11 = tmp1 + tmp2;
     141               0 :     tmp12 = tmp1 - tmp2;
     142                 :     
     143               0 :     dataptr[0] = tmp10 + tmp11; /* phase 3 */
     144               0 :     dataptr[4] = tmp10 - tmp11;
     145                 :     
     146               0 :     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
     147               0 :     dataptr[2] = tmp13 + z1;    /* phase 5 */
     148               0 :     dataptr[6] = tmp13 - z1;
     149                 :     
     150                 :     /* Odd part */
     151                 : 
     152               0 :     tmp10 = tmp4 + tmp5;        /* phase 2 */
     153               0 :     tmp11 = tmp5 + tmp6;
     154               0 :     tmp12 = tmp6 + tmp7;
     155                 : 
     156                 :     /* The rotator is modified from fig 4-8 to avoid extra negations. */
     157               0 :     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
     158               0 :     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
     159               0 :     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
     160               0 :     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
     161                 : 
     162               0 :     z11 = tmp7 + z3;            /* phase 5 */
     163               0 :     z13 = tmp7 - z3;
     164                 : 
     165               0 :     dataptr[5] = z13 + z2;      /* phase 6 */
     166               0 :     dataptr[3] = z13 - z2;
     167               0 :     dataptr[1] = z11 + z4;
     168               0 :     dataptr[7] = z11 - z4;
     169                 : 
     170               0 :     dataptr += DCTSIZE;         /* advance pointer to next row */
     171                 :   }
     172                 : 
     173                 :   /* Pass 2: process columns. */
     174                 : 
     175               0 :   dataptr = data;
     176               0 :   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
     177               0 :     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
     178               0 :     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
     179               0 :     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
     180               0 :     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
     181               0 :     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
     182               0 :     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
     183               0 :     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
     184               0 :     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
     185                 :     
     186                 :     /* Even part */
     187                 :     
     188               0 :     tmp10 = tmp0 + tmp3;        /* phase 2 */
     189               0 :     tmp13 = tmp0 - tmp3;
     190               0 :     tmp11 = tmp1 + tmp2;
     191               0 :     tmp12 = tmp1 - tmp2;
     192                 :     
     193               0 :     dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
     194               0 :     dataptr[DCTSIZE*4] = tmp10 - tmp11;
     195                 :     
     196               0 :     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
     197               0 :     dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
     198               0 :     dataptr[DCTSIZE*6] = tmp13 - z1;
     199                 :     
     200                 :     /* Odd part */
     201                 : 
     202               0 :     tmp10 = tmp4 + tmp5;        /* phase 2 */
     203               0 :     tmp11 = tmp5 + tmp6;
     204               0 :     tmp12 = tmp6 + tmp7;
     205                 : 
     206                 :     /* The rotator is modified from fig 4-8 to avoid extra negations. */
     207               0 :     z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
     208               0 :     z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
     209               0 :     z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
     210               0 :     z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
     211                 : 
     212               0 :     z11 = tmp7 + z3;            /* phase 5 */
     213               0 :     z13 = tmp7 - z3;
     214                 : 
     215               0 :     dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
     216               0 :     dataptr[DCTSIZE*3] = z13 - z2;
     217               0 :     dataptr[DCTSIZE*1] = z11 + z4;
     218               0 :     dataptr[DCTSIZE*7] = z11 - z4;
     219                 : 
     220               0 :     dataptr++;                  /* advance pointer to next column */
     221                 :   }
     222               0 : }
     223                 : 
     224                 : #endif /* DCT_IFAST_SUPPORTED */

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