media/libjpeg/jfdctflt.c

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