compiler/libjpeg/main/jfdctflt.c

   1 /*
   2     $Id$
   3 */
   4
   5 /*
   6  * jfdctflt.c
   7  *
   8  * Copyright (C) 1994-1996, Thomas G. Lane.
   9  * This file is part of the Independent JPEG Group's software.
  10  * For conditions of distribution and use, see the accompanying README file.
  11  *
  12  * This file contains a floating-point implementation of the
  13  * forward DCT (Discrete Cosine Transform).
  14  *
  15  * This implementation should be more accurate than either of the integer
  16  * DCT implementations.  However, it may not give the same results on all
  17  * machines because of differences in roundoff behavior.  Speed will depend
  18  * on the hardware's floating point capacity.
  19  *
  20  * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
  21  * on each column.  Direct algorithms are also available, but they are
  22  * much more complex and seem not to be any faster when reduced to code.
  23  *
  24  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
  25  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  26  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
  27  * JPEG textbook (see REFERENCES section in file README).  The following code
  28  * is based directly on figure 4-8 in P&M.
  29  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  30  * possible to arrange the computation so that many of the multiplies are
  31  * simple scalings of the final outputs.  These multiplies can then be
  32  * folded into the multiplications or divisions by the JPEG quantization
  33  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
  34  * to be done in the DCT itself.
  35  * The primary disadvantage of this method is that with a fixed-point
  36  * implementation, accuracy is lost due to imprecise representation of the
  37  * scaled quantization values.  However, that problem does not arise if
  38  * we use floating point arithmetic.
  39  */
  40
  41 #define JPEG_INTERNALS
  42 #include "jinclude.h"
  43 #include "jpeglib.h"
  44 #include "jdct.h"               /* Private declarations for DCT subsystem */
  45
  46 #ifdef DCT_FLOAT_SUPPORTED
  47
  48
  49 /*
  50  * This module is specialized to the case DCTSIZE = 8.
  51  */
  52
  53 #if DCTSIZE != 8
  54   Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
  55 #endif
  56
  57
  58 /*
  59  * Perform the forward DCT on one block of samples.
  60  */
  61
  62 JGLOBAL(void)
  63 jpeg_fdct_float (FAST_FLOAT * data)
  64 {
  65   FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  66   FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
  67   FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
  68   FAST_FLOAT *dataptr;
  69   int ctr;
  70
  71   /* Pass 1: process rows. */
  72
  73   dataptr = data;
  74   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
  75     tmp0 = dataptr[0] + dataptr[7];
  76     tmp7 = dataptr[0] - dataptr[7];
  77     tmp1 = dataptr[1] + dataptr[6];
  78     tmp6 = dataptr[1] - dataptr[6];
  79     tmp2 = dataptr[2] + dataptr[5];
  80     tmp5 = dataptr[2] - dataptr[5];
  81     tmp3 = dataptr[3] + dataptr[4];
  82     tmp4 = dataptr[3] - dataptr[4];
  83
  84     /* Even part */
  85
  86     tmp10 = tmp0 + tmp3;        /* phase 2 */
  87     tmp13 = tmp0 - tmp3;
  88     tmp11 = tmp1 + tmp2;
  89     tmp12 = tmp1 - tmp2;
  90
  91     dataptr[0] = tmp10 + tmp11; /* phase 3 */
  92     dataptr[4] = tmp10 - tmp11;
  93
  94     z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
  95     dataptr[2] = tmp13 + z1;    /* phase 5 */
  96     dataptr[6] = tmp13 - z1;
  97
  98     /* Odd part */
  99
 100     tmp10 = tmp4 + tmp5;        /* phase 2 */
 101     tmp11 = tmp5 + tmp6;
 102     tmp12 = tmp6 + tmp7;
 103
 104     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 105     z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
 106     z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
 107     z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
 108     z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
 109
 110     z11 = tmp7 + z3;            /* phase 5 */
 111     z13 = tmp7 - z3;
 112
 113     dataptr[5] = z13 + z2;      /* phase 6 */
 114     dataptr[3] = z13 - z2;
 115     dataptr[1] = z11 + z4;
 116     dataptr[7] = z11 - z4;
 117
 118     dataptr += DCTSIZE;         /* advance pointer to next row */
 119   }
 120
 121   /* Pass 2: process columns. */
 122
 123   dataptr = data;
 124   for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
 125     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
 126     tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
 127     tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
 128     tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
 129     tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
 130     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
 131     tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
 132     tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
 133
 134     /* Even part */
 135
 136     tmp10 = tmp0 + tmp3;        /* phase 2 */
 137     tmp13 = tmp0 - tmp3;
 138     tmp11 = tmp1 + tmp2;
 139     tmp12 = tmp1 - tmp2;
 140
 141     dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
 142     dataptr[DCTSIZE*4] = tmp10 - tmp11;
 143
 144     z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
 145     dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
 146     dataptr[DCTSIZE*6] = tmp13 - z1;
 147
 148     /* Odd part */
 149
 150     tmp10 = tmp4 + tmp5;        /* phase 2 */
 151     tmp11 = tmp5 + tmp6;
 152     tmp12 = tmp6 + tmp7;
 153
 154     /* The rotator is modified from fig 4-8 to avoid extra negations. */
 155     z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
 156     z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
 157     z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
 158     z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
 159
 160     z11 = tmp7 + z3;            /* phase 5 */
 161     z13 = tmp7 - z3;
 162
 163     dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
 164     dataptr[DCTSIZE*3] = z13 - z2;
 165     dataptr[DCTSIZE*1] = z11 + z4;
 166     dataptr[DCTSIZE*7] = z11 - z4;
 167
 168     dataptr++;                  /* advance pointer to next column */
 169   }
 170 }
 171
 172 #endif /* DCT_FLOAT_SUPPORTED */