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/src/FreeImage/Source/LibJPEG/jfdctflt.c

https://bitbucket.org/cabalistic/ogredeps/
C | 174 lines | 88 code | 34 blank | 52 comment | 3 complexity | e6e25112dbfbd691bbac5585c4d74c0b MD5 | raw file
  1/*
  2 * jfdctflt.c
  3 *
  4 * Copyright (C) 1994-1996, Thomas G. Lane.
  5 * Modified 2003-2009 by Guido Vollbeding.
  6 * This file is part of the Independent JPEG Group's software.
  7 * For conditions of distribution and use, see the accompanying README 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).  The following code
 25 * 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
 59GLOBAL(void)
 60jpeg_fdct_float (FAST_FLOAT * data, JSAMPARRAY sample_data, JDIMENSION start_col)
 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  JSAMPROW elemptr;
 67  int ctr;
 68
 69  /* Pass 1: process rows. */
 70
 71  dataptr = data;
 72  for (ctr = 0; ctr < DCTSIZE; ctr++) {
 73    elemptr = sample_data[ctr] + start_col;
 74
 75    /* Load data into workspace */
 76    tmp0 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) + GETJSAMPLE(elemptr[7]));
 77    tmp7 = (FAST_FLOAT) (GETJSAMPLE(elemptr[0]) - GETJSAMPLE(elemptr[7]));
 78    tmp1 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) + GETJSAMPLE(elemptr[6]));
 79    tmp6 = (FAST_FLOAT) (GETJSAMPLE(elemptr[1]) - GETJSAMPLE(elemptr[6]));
 80    tmp2 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) + GETJSAMPLE(elemptr[5]));
 81    tmp5 = (FAST_FLOAT) (GETJSAMPLE(elemptr[2]) - GETJSAMPLE(elemptr[5]));
 82    tmp3 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) + GETJSAMPLE(elemptr[4]));
 83    tmp4 = (FAST_FLOAT) (GETJSAMPLE(elemptr[3]) - GETJSAMPLE(elemptr[4]));
 84
 85    /* Even part */
 86
 87    tmp10 = tmp0 + tmp3;	/* phase 2 */
 88    tmp13 = tmp0 - tmp3;
 89    tmp11 = tmp1 + tmp2;
 90    tmp12 = tmp1 - tmp2;
 91
 92    /* Apply unsigned->signed conversion */
 93    dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
 94    dataptr[4] = tmp10 - tmp11;
 95
 96    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
 97    dataptr[2] = tmp13 + z1;	/* phase 5 */
 98    dataptr[6] = tmp13 - z1;
 99
100    /* Odd part */
101
102    tmp10 = tmp4 + tmp5;	/* phase 2 */
103    tmp11 = tmp5 + tmp6;
104    tmp12 = tmp6 + tmp7;
105
106    /* The rotator is modified from fig 4-8 to avoid extra negations. */
107    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
108    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
109    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
110    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
111
112    z11 = tmp7 + z3;		/* phase 5 */
113    z13 = tmp7 - z3;
114
115    dataptr[5] = z13 + z2;	/* phase 6 */
116    dataptr[3] = z13 - z2;
117    dataptr[1] = z11 + z4;
118    dataptr[7] = z11 - z4;
119
120    dataptr += DCTSIZE;		/* advance pointer to next row */
121  }
122
123  /* Pass 2: process columns. */
124
125  dataptr = data;
126  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
127    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
128    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
129    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
130    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
131    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
132    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
133    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
134    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
135
136    /* Even part */
137
138    tmp10 = tmp0 + tmp3;	/* phase 2 */
139    tmp13 = tmp0 - tmp3;
140    tmp11 = tmp1 + tmp2;
141    tmp12 = tmp1 - tmp2;
142
143    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
144    dataptr[DCTSIZE*4] = tmp10 - tmp11;
145
146    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
147    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
148    dataptr[DCTSIZE*6] = tmp13 - z1;
149
150    /* Odd part */
151
152    tmp10 = tmp4 + tmp5;	/* phase 2 */
153    tmp11 = tmp5 + tmp6;
154    tmp12 = tmp6 + tmp7;
155
156    /* The rotator is modified from fig 4-8 to avoid extra negations. */
157    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
158    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
159    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
160    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */
161
162    z11 = tmp7 + z3;		/* phase 5 */
163    z13 = tmp7 - z3;
164
165    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
166    dataptr[DCTSIZE*3] = z13 - z2;
167    dataptr[DCTSIZE*1] = z11 + z4;
168    dataptr[DCTSIZE*7] = z11 - z4;
169
170    dataptr++;			/* advance pointer to next column */
171  }
172}
173
174#endif /* DCT_FLOAT_SUPPORTED */