dbf-halloween2015

annotate libs/libjpeg/jfdctfst.c @ 3:c37fe5d8a4ed

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author John Tsiombikas <nuclear@member.fsf.org>
date Sun, 01 Nov 2015 06:04:28 +0200
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nuclear@1 1 /*
nuclear@1 2 * jfdctfst.c
nuclear@1 3 *
nuclear@1 4 * Copyright (C) 1994-1996, Thomas G. Lane.
nuclear@1 5 * This file is part of the Independent JPEG Group's software.
nuclear@1 6 * For conditions of distribution and use, see the accompanying README file.
nuclear@1 7 *
nuclear@1 8 * This file contains a fast, not so accurate integer implementation of the
nuclear@1 9 * forward DCT (Discrete Cosine Transform).
nuclear@1 10 *
nuclear@1 11 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
nuclear@1 12 * on each column. Direct algorithms are also available, but they are
nuclear@1 13 * much more complex and seem not to be any faster when reduced to code.
nuclear@1 14 *
nuclear@1 15 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
nuclear@1 16 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
nuclear@1 17 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
nuclear@1 18 * JPEG textbook (see REFERENCES section in file README). The following code
nuclear@1 19 * is based directly on figure 4-8 in P&M.
nuclear@1 20 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
nuclear@1 21 * possible to arrange the computation so that many of the multiplies are
nuclear@1 22 * simple scalings of the final outputs. These multiplies can then be
nuclear@1 23 * folded into the multiplications or divisions by the JPEG quantization
nuclear@1 24 * table entries. The AA&N method leaves only 5 multiplies and 29 adds
nuclear@1 25 * to be done in the DCT itself.
nuclear@1 26 * The primary disadvantage of this method is that with fixed-point math,
nuclear@1 27 * accuracy is lost due to imprecise representation of the scaled
nuclear@1 28 * quantization values. The smaller the quantization table entry, the less
nuclear@1 29 * precise the scaled value, so this implementation does worse with high-
nuclear@1 30 * quality-setting files than with low-quality ones.
nuclear@1 31 */
nuclear@1 32
nuclear@1 33 #define JPEG_INTERNALS
nuclear@1 34 #include "jinclude.h"
nuclear@1 35 #include "jpeglib.h"
nuclear@1 36 #include "jdct.h" /* Private declarations for DCT subsystem */
nuclear@1 37
nuclear@1 38 #ifdef DCT_IFAST_SUPPORTED
nuclear@1 39
nuclear@1 40
nuclear@1 41 /*
nuclear@1 42 * This module is specialized to the case DCTSIZE = 8.
nuclear@1 43 */
nuclear@1 44
nuclear@1 45 #if DCTSIZE != 8
nuclear@1 46 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
nuclear@1 47 #endif
nuclear@1 48
nuclear@1 49
nuclear@1 50 /* Scaling decisions are generally the same as in the LL&M algorithm;
nuclear@1 51 * see jfdctint.c for more details. However, we choose to descale
nuclear@1 52 * (right shift) multiplication products as soon as they are formed,
nuclear@1 53 * rather than carrying additional fractional bits into subsequent additions.
nuclear@1 54 * This compromises accuracy slightly, but it lets us save a few shifts.
nuclear@1 55 * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
nuclear@1 56 * everywhere except in the multiplications proper; this saves a good deal
nuclear@1 57 * of work on 16-bit-int machines.
nuclear@1 58 *
nuclear@1 59 * Again to save a few shifts, the intermediate results between pass 1 and
nuclear@1 60 * pass 2 are not upscaled, but are represented only to integral precision.
nuclear@1 61 *
nuclear@1 62 * A final compromise is to represent the multiplicative constants to only
nuclear@1 63 * 8 fractional bits, rather than 13. This saves some shifting work on some
nuclear@1 64 * machines, and may also reduce the cost of multiplication (since there
nuclear@1 65 * are fewer one-bits in the constants).
nuclear@1 66 */
nuclear@1 67
nuclear@1 68 #define CONST_BITS 8
nuclear@1 69
nuclear@1 70
nuclear@1 71 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
nuclear@1 72 * causing a lot of useless floating-point operations at run time.
nuclear@1 73 * To get around this we use the following pre-calculated constants.
nuclear@1 74 * If you change CONST_BITS you may want to add appropriate values.
nuclear@1 75 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
nuclear@1 76 */
nuclear@1 77
nuclear@1 78 #if CONST_BITS == 8
nuclear@1 79 #define FIX_0_382683433 ((INT32) 98) /* FIX(0.382683433) */
nuclear@1 80 #define FIX_0_541196100 ((INT32) 139) /* FIX(0.541196100) */
nuclear@1 81 #define FIX_0_707106781 ((INT32) 181) /* FIX(0.707106781) */
nuclear@1 82 #define FIX_1_306562965 ((INT32) 334) /* FIX(1.306562965) */
nuclear@1 83 #else
nuclear@1 84 #define FIX_0_382683433 FIX(0.382683433)
nuclear@1 85 #define FIX_0_541196100 FIX(0.541196100)
nuclear@1 86 #define FIX_0_707106781 FIX(0.707106781)
nuclear@1 87 #define FIX_1_306562965 FIX(1.306562965)
nuclear@1 88 #endif
nuclear@1 89
nuclear@1 90
nuclear@1 91 /* We can gain a little more speed, with a further compromise in accuracy,
nuclear@1 92 * by omitting the addition in a descaling shift. This yields an incorrectly
nuclear@1 93 * rounded result half the time...
nuclear@1 94 */
nuclear@1 95
nuclear@1 96 #ifndef USE_ACCURATE_ROUNDING
nuclear@1 97 #undef DESCALE
nuclear@1 98 #define DESCALE(x,n) RIGHT_SHIFT(x, n)
nuclear@1 99 #endif
nuclear@1 100
nuclear@1 101
nuclear@1 102 /* Multiply a DCTELEM variable by an INT32 constant, and immediately
nuclear@1 103 * descale to yield a DCTELEM result.
nuclear@1 104 */
nuclear@1 105
nuclear@1 106 #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
nuclear@1 107
nuclear@1 108
nuclear@1 109 /*
nuclear@1 110 * Perform the forward DCT on one block of samples.
nuclear@1 111 */
nuclear@1 112
nuclear@1 113 GLOBAL(void)
nuclear@1 114 jpeg_fdct_ifast (DCTELEM * data)
nuclear@1 115 {
nuclear@1 116 DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
nuclear@1 117 DCTELEM tmp10, tmp11, tmp12, tmp13;
nuclear@1 118 DCTELEM z1, z2, z3, z4, z5, z11, z13;
nuclear@1 119 DCTELEM *dataptr;
nuclear@1 120 int ctr;
nuclear@1 121 SHIFT_TEMPS
nuclear@1 122
nuclear@1 123 /* Pass 1: process rows. */
nuclear@1 124
nuclear@1 125 dataptr = data;
nuclear@1 126 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
nuclear@1 127 tmp0 = dataptr[0] + dataptr[7];
nuclear@1 128 tmp7 = dataptr[0] - dataptr[7];
nuclear@1 129 tmp1 = dataptr[1] + dataptr[6];
nuclear@1 130 tmp6 = dataptr[1] - dataptr[6];
nuclear@1 131 tmp2 = dataptr[2] + dataptr[5];
nuclear@1 132 tmp5 = dataptr[2] - dataptr[5];
nuclear@1 133 tmp3 = dataptr[3] + dataptr[4];
nuclear@1 134 tmp4 = dataptr[3] - dataptr[4];
nuclear@1 135
nuclear@1 136 /* Even part */
nuclear@1 137
nuclear@1 138 tmp10 = tmp0 + tmp3; /* phase 2 */
nuclear@1 139 tmp13 = tmp0 - tmp3;
nuclear@1 140 tmp11 = tmp1 + tmp2;
nuclear@1 141 tmp12 = tmp1 - tmp2;
nuclear@1 142
nuclear@1 143 dataptr[0] = tmp10 + tmp11; /* phase 3 */
nuclear@1 144 dataptr[4] = tmp10 - tmp11;
nuclear@1 145
nuclear@1 146 z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
nuclear@1 147 dataptr[2] = tmp13 + z1; /* phase 5 */
nuclear@1 148 dataptr[6] = tmp13 - z1;
nuclear@1 149
nuclear@1 150 /* Odd part */
nuclear@1 151
nuclear@1 152 tmp10 = tmp4 + tmp5; /* phase 2 */
nuclear@1 153 tmp11 = tmp5 + tmp6;
nuclear@1 154 tmp12 = tmp6 + tmp7;
nuclear@1 155
nuclear@1 156 /* The rotator is modified from fig 4-8 to avoid extra negations. */
nuclear@1 157 z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
nuclear@1 158 z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
nuclear@1 159 z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
nuclear@1 160 z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
nuclear@1 161
nuclear@1 162 z11 = tmp7 + z3; /* phase 5 */
nuclear@1 163 z13 = tmp7 - z3;
nuclear@1 164
nuclear@1 165 dataptr[5] = z13 + z2; /* phase 6 */
nuclear@1 166 dataptr[3] = z13 - z2;
nuclear@1 167 dataptr[1] = z11 + z4;
nuclear@1 168 dataptr[7] = z11 - z4;
nuclear@1 169
nuclear@1 170 dataptr += DCTSIZE; /* advance pointer to next row */
nuclear@1 171 }
nuclear@1 172
nuclear@1 173 /* Pass 2: process columns. */
nuclear@1 174
nuclear@1 175 dataptr = data;
nuclear@1 176 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
nuclear@1 177 tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
nuclear@1 178 tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
nuclear@1 179 tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
nuclear@1 180 tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
nuclear@1 181 tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
nuclear@1 182 tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
nuclear@1 183 tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
nuclear@1 184 tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
nuclear@1 185
nuclear@1 186 /* Even part */
nuclear@1 187
nuclear@1 188 tmp10 = tmp0 + tmp3; /* phase 2 */
nuclear@1 189 tmp13 = tmp0 - tmp3;
nuclear@1 190 tmp11 = tmp1 + tmp2;
nuclear@1 191 tmp12 = tmp1 - tmp2;
nuclear@1 192
nuclear@1 193 dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
nuclear@1 194 dataptr[DCTSIZE*4] = tmp10 - tmp11;
nuclear@1 195
nuclear@1 196 z1 = MULTIPLY(tmp12 + tmp13, FIX_0_707106781); /* c4 */
nuclear@1 197 dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
nuclear@1 198 dataptr[DCTSIZE*6] = tmp13 - z1;
nuclear@1 199
nuclear@1 200 /* Odd part */
nuclear@1 201
nuclear@1 202 tmp10 = tmp4 + tmp5; /* phase 2 */
nuclear@1 203 tmp11 = tmp5 + tmp6;
nuclear@1 204 tmp12 = tmp6 + tmp7;
nuclear@1 205
nuclear@1 206 /* The rotator is modified from fig 4-8 to avoid extra negations. */
nuclear@1 207 z5 = MULTIPLY(tmp10 - tmp12, FIX_0_382683433); /* c6 */
nuclear@1 208 z2 = MULTIPLY(tmp10, FIX_0_541196100) + z5; /* c2-c6 */
nuclear@1 209 z4 = MULTIPLY(tmp12, FIX_1_306562965) + z5; /* c2+c6 */
nuclear@1 210 z3 = MULTIPLY(tmp11, FIX_0_707106781); /* c4 */
nuclear@1 211
nuclear@1 212 z11 = tmp7 + z3; /* phase 5 */
nuclear@1 213 z13 = tmp7 - z3;
nuclear@1 214
nuclear@1 215 dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
nuclear@1 216 dataptr[DCTSIZE*3] = z13 - z2;
nuclear@1 217 dataptr[DCTSIZE*1] = z11 + z4;
nuclear@1 218 dataptr[DCTSIZE*7] = z11 - z4;
nuclear@1 219
nuclear@1 220 dataptr++; /* advance pointer to next column */
nuclear@1 221 }
nuclear@1 222 }
nuclear@1 223
nuclear@1 224 #endif /* DCT_IFAST_SUPPORTED */