dbf-halloween2015

annotate libs/libjpeg/jidctfst.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 * jidctfst.c
nuclear@1 3 *
nuclear@1 4 * Copyright (C) 1994-1998, 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 * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
nuclear@1 10 * must also perform dequantization of the input coefficients.
nuclear@1 11 *
nuclear@1 12 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
nuclear@1 13 * on each row (or vice versa, but it's more convenient to emit a row at
nuclear@1 14 * a time). Direct algorithms are also available, but they are much more
nuclear@1 15 * complex and seem not to be any faster when reduced to code.
nuclear@1 16 *
nuclear@1 17 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
nuclear@1 18 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
nuclear@1 19 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
nuclear@1 20 * JPEG textbook (see REFERENCES section in file README). The following code
nuclear@1 21 * is based directly on figure 4-8 in P&M.
nuclear@1 22 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
nuclear@1 23 * possible to arrange the computation so that many of the multiplies are
nuclear@1 24 * simple scalings of the final outputs. These multiplies can then be
nuclear@1 25 * folded into the multiplications or divisions by the JPEG quantization
nuclear@1 26 * table entries. The AA&N method leaves only 5 multiplies and 29 adds
nuclear@1 27 * to be done in the DCT itself.
nuclear@1 28 * The primary disadvantage of this method is that with fixed-point math,
nuclear@1 29 * accuracy is lost due to imprecise representation of the scaled
nuclear@1 30 * quantization values. The smaller the quantization table entry, the less
nuclear@1 31 * precise the scaled value, so this implementation does worse with high-
nuclear@1 32 * quality-setting files than with low-quality ones.
nuclear@1 33 */
nuclear@1 34
nuclear@1 35 #define JPEG_INTERNALS
nuclear@1 36 #include "jinclude.h"
nuclear@1 37 #include "jpeglib.h"
nuclear@1 38 #include "jdct.h" /* Private declarations for DCT subsystem */
nuclear@1 39
nuclear@1 40 #ifdef DCT_IFAST_SUPPORTED
nuclear@1 41
nuclear@1 42
nuclear@1 43 /*
nuclear@1 44 * This module is specialized to the case DCTSIZE = 8.
nuclear@1 45 */
nuclear@1 46
nuclear@1 47 #if DCTSIZE != 8
nuclear@1 48 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
nuclear@1 49 #endif
nuclear@1 50
nuclear@1 51
nuclear@1 52 /* Scaling decisions are generally the same as in the LL&M algorithm;
nuclear@1 53 * see jidctint.c for more details. However, we choose to descale
nuclear@1 54 * (right shift) multiplication products as soon as they are formed,
nuclear@1 55 * rather than carrying additional fractional bits into subsequent additions.
nuclear@1 56 * This compromises accuracy slightly, but it lets us save a few shifts.
nuclear@1 57 * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
nuclear@1 58 * everywhere except in the multiplications proper; this saves a good deal
nuclear@1 59 * of work on 16-bit-int machines.
nuclear@1 60 *
nuclear@1 61 * The dequantized coefficients are not integers because the AA&N scaling
nuclear@1 62 * factors have been incorporated. We represent them scaled up by PASS1_BITS,
nuclear@1 63 * so that the first and second IDCT rounds have the same input scaling.
nuclear@1 64 * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to
nuclear@1 65 * avoid a descaling shift; this compromises accuracy rather drastically
nuclear@1 66 * for small quantization table entries, but it saves a lot of shifts.
nuclear@1 67 * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,
nuclear@1 68 * so we use a much larger scaling factor to preserve accuracy.
nuclear@1 69 *
nuclear@1 70 * A final compromise is to represent the multiplicative constants to only
nuclear@1 71 * 8 fractional bits, rather than 13. This saves some shifting work on some
nuclear@1 72 * machines, and may also reduce the cost of multiplication (since there
nuclear@1 73 * are fewer one-bits in the constants).
nuclear@1 74 */
nuclear@1 75
nuclear@1 76 #if BITS_IN_JSAMPLE == 8
nuclear@1 77 #define CONST_BITS 8
nuclear@1 78 #define PASS1_BITS 2
nuclear@1 79 #else
nuclear@1 80 #define CONST_BITS 8
nuclear@1 81 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */
nuclear@1 82 #endif
nuclear@1 83
nuclear@1 84 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
nuclear@1 85 * causing a lot of useless floating-point operations at run time.
nuclear@1 86 * To get around this we use the following pre-calculated constants.
nuclear@1 87 * If you change CONST_BITS you may want to add appropriate values.
nuclear@1 88 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
nuclear@1 89 */
nuclear@1 90
nuclear@1 91 #if CONST_BITS == 8
nuclear@1 92 #define FIX_1_082392200 ((INT32) 277) /* FIX(1.082392200) */
nuclear@1 93 #define FIX_1_414213562 ((INT32) 362) /* FIX(1.414213562) */
nuclear@1 94 #define FIX_1_847759065 ((INT32) 473) /* FIX(1.847759065) */
nuclear@1 95 #define FIX_2_613125930 ((INT32) 669) /* FIX(2.613125930) */
nuclear@1 96 #else
nuclear@1 97 #define FIX_1_082392200 FIX(1.082392200)
nuclear@1 98 #define FIX_1_414213562 FIX(1.414213562)
nuclear@1 99 #define FIX_1_847759065 FIX(1.847759065)
nuclear@1 100 #define FIX_2_613125930 FIX(2.613125930)
nuclear@1 101 #endif
nuclear@1 102
nuclear@1 103
nuclear@1 104 /* We can gain a little more speed, with a further compromise in accuracy,
nuclear@1 105 * by omitting the addition in a descaling shift. This yields an incorrectly
nuclear@1 106 * rounded result half the time...
nuclear@1 107 */
nuclear@1 108
nuclear@1 109 #ifndef USE_ACCURATE_ROUNDING
nuclear@1 110 #undef DESCALE
nuclear@1 111 #define DESCALE(x,n) RIGHT_SHIFT(x, n)
nuclear@1 112 #endif
nuclear@1 113
nuclear@1 114
nuclear@1 115 /* Multiply a DCTELEM variable by an INT32 constant, and immediately
nuclear@1 116 * descale to yield a DCTELEM result.
nuclear@1 117 */
nuclear@1 118
nuclear@1 119 #define MULTIPLY(var,const) ((DCTELEM) DESCALE((var) * (const), CONST_BITS))
nuclear@1 120
nuclear@1 121
nuclear@1 122 /* Dequantize a coefficient by multiplying it by the multiplier-table
nuclear@1 123 * entry; produce a DCTELEM result. For 8-bit data a 16x16->16
nuclear@1 124 * multiplication will do. For 12-bit data, the multiplier table is
nuclear@1 125 * declared INT32, so a 32-bit multiply will be used.
nuclear@1 126 */
nuclear@1 127
nuclear@1 128 #if BITS_IN_JSAMPLE == 8
nuclear@1 129 #define DEQUANTIZE(coef,quantval) (((IFAST_MULT_TYPE) (coef)) * (quantval))
nuclear@1 130 #else
nuclear@1 131 #define DEQUANTIZE(coef,quantval) \
nuclear@1 132 DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS)
nuclear@1 133 #endif
nuclear@1 134
nuclear@1 135
nuclear@1 136 /* Like DESCALE, but applies to a DCTELEM and produces an int.
nuclear@1 137 * We assume that int right shift is unsigned if INT32 right shift is.
nuclear@1 138 */
nuclear@1 139
nuclear@1 140 #ifdef RIGHT_SHIFT_IS_UNSIGNED
nuclear@1 141 #define ISHIFT_TEMPS DCTELEM ishift_temp;
nuclear@1 142 #if BITS_IN_JSAMPLE == 8
nuclear@1 143 #define DCTELEMBITS 16 /* DCTELEM may be 16 or 32 bits */
nuclear@1 144 #else
nuclear@1 145 #define DCTELEMBITS 32 /* DCTELEM must be 32 bits */
nuclear@1 146 #endif
nuclear@1 147 #define IRIGHT_SHIFT(x,shft) \
nuclear@1 148 ((ishift_temp = (x)) < 0 ? \
nuclear@1 149 (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \
nuclear@1 150 (ishift_temp >> (shft)))
nuclear@1 151 #else
nuclear@1 152 #define ISHIFT_TEMPS
nuclear@1 153 #define IRIGHT_SHIFT(x,shft) ((x) >> (shft))
nuclear@1 154 #endif
nuclear@1 155
nuclear@1 156 #ifdef USE_ACCURATE_ROUNDING
nuclear@1 157 #define IDESCALE(x,n) ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
nuclear@1 158 #else
nuclear@1 159 #define IDESCALE(x,n) ((int) IRIGHT_SHIFT(x, n))
nuclear@1 160 #endif
nuclear@1 161
nuclear@1 162
nuclear@1 163 /*
nuclear@1 164 * Perform dequantization and inverse DCT on one block of coefficients.
nuclear@1 165 */
nuclear@1 166
nuclear@1 167 GLOBAL(void)
nuclear@1 168 jpeg_idct_ifast (j_decompress_ptr cinfo, jpeg_component_info * compptr,
nuclear@1 169 JCOEFPTR coef_block,
nuclear@1 170 JSAMPARRAY output_buf, JDIMENSION output_col)
nuclear@1 171 {
nuclear@1 172 DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
nuclear@1 173 DCTELEM tmp10, tmp11, tmp12, tmp13;
nuclear@1 174 DCTELEM z5, z10, z11, z12, z13;
nuclear@1 175 JCOEFPTR inptr;
nuclear@1 176 IFAST_MULT_TYPE * quantptr;
nuclear@1 177 int * wsptr;
nuclear@1 178 JSAMPROW outptr;
nuclear@1 179 JSAMPLE *range_limit = IDCT_range_limit(cinfo);
nuclear@1 180 int ctr;
nuclear@1 181 int workspace[DCTSIZE2]; /* buffers data between passes */
nuclear@1 182 SHIFT_TEMPS /* for DESCALE */
nuclear@1 183 ISHIFT_TEMPS /* for IDESCALE */
nuclear@1 184
nuclear@1 185 /* Pass 1: process columns from input, store into work array. */
nuclear@1 186
nuclear@1 187 inptr = coef_block;
nuclear@1 188 quantptr = (IFAST_MULT_TYPE *) compptr->dct_table;
nuclear@1 189 wsptr = workspace;
nuclear@1 190 for (ctr = DCTSIZE; ctr > 0; ctr--) {
nuclear@1 191 /* Due to quantization, we will usually find that many of the input
nuclear@1 192 * coefficients are zero, especially the AC terms. We can exploit this
nuclear@1 193 * by short-circuiting the IDCT calculation for any column in which all
nuclear@1 194 * the AC terms are zero. In that case each output is equal to the
nuclear@1 195 * DC coefficient (with scale factor as needed).
nuclear@1 196 * With typical images and quantization tables, half or more of the
nuclear@1 197 * column DCT calculations can be simplified this way.
nuclear@1 198 */
nuclear@1 199
nuclear@1 200 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
nuclear@1 201 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
nuclear@1 202 inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
nuclear@1 203 inptr[DCTSIZE*7] == 0) {
nuclear@1 204 /* AC terms all zero */
nuclear@1 205 int dcval = (int) DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
nuclear@1 206
nuclear@1 207 wsptr[DCTSIZE*0] = dcval;
nuclear@1 208 wsptr[DCTSIZE*1] = dcval;
nuclear@1 209 wsptr[DCTSIZE*2] = dcval;
nuclear@1 210 wsptr[DCTSIZE*3] = dcval;
nuclear@1 211 wsptr[DCTSIZE*4] = dcval;
nuclear@1 212 wsptr[DCTSIZE*5] = dcval;
nuclear@1 213 wsptr[DCTSIZE*6] = dcval;
nuclear@1 214 wsptr[DCTSIZE*7] = dcval;
nuclear@1 215
nuclear@1 216 inptr++; /* advance pointers to next column */
nuclear@1 217 quantptr++;
nuclear@1 218 wsptr++;
nuclear@1 219 continue;
nuclear@1 220 }
nuclear@1 221
nuclear@1 222 /* Even part */
nuclear@1 223
nuclear@1 224 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
nuclear@1 225 tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
nuclear@1 226 tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
nuclear@1 227 tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
nuclear@1 228
nuclear@1 229 tmp10 = tmp0 + tmp2; /* phase 3 */
nuclear@1 230 tmp11 = tmp0 - tmp2;
nuclear@1 231
nuclear@1 232 tmp13 = tmp1 + tmp3; /* phases 5-3 */
nuclear@1 233 tmp12 = MULTIPLY(tmp1 - tmp3, FIX_1_414213562) - tmp13; /* 2*c4 */
nuclear@1 234
nuclear@1 235 tmp0 = tmp10 + tmp13; /* phase 2 */
nuclear@1 236 tmp3 = tmp10 - tmp13;
nuclear@1 237 tmp1 = tmp11 + tmp12;
nuclear@1 238 tmp2 = tmp11 - tmp12;
nuclear@1 239
nuclear@1 240 /* Odd part */
nuclear@1 241
nuclear@1 242 tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
nuclear@1 243 tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
nuclear@1 244 tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
nuclear@1 245 tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
nuclear@1 246
nuclear@1 247 z13 = tmp6 + tmp5; /* phase 6 */
nuclear@1 248 z10 = tmp6 - tmp5;
nuclear@1 249 z11 = tmp4 + tmp7;
nuclear@1 250 z12 = tmp4 - tmp7;
nuclear@1 251
nuclear@1 252 tmp7 = z11 + z13; /* phase 5 */
nuclear@1 253 tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
nuclear@1 254
nuclear@1 255 z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
nuclear@1 256 tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
nuclear@1 257 tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
nuclear@1 258
nuclear@1 259 tmp6 = tmp12 - tmp7; /* phase 2 */
nuclear@1 260 tmp5 = tmp11 - tmp6;
nuclear@1 261 tmp4 = tmp10 + tmp5;
nuclear@1 262
nuclear@1 263 wsptr[DCTSIZE*0] = (int) (tmp0 + tmp7);
nuclear@1 264 wsptr[DCTSIZE*7] = (int) (tmp0 - tmp7);
nuclear@1 265 wsptr[DCTSIZE*1] = (int) (tmp1 + tmp6);
nuclear@1 266 wsptr[DCTSIZE*6] = (int) (tmp1 - tmp6);
nuclear@1 267 wsptr[DCTSIZE*2] = (int) (tmp2 + tmp5);
nuclear@1 268 wsptr[DCTSIZE*5] = (int) (tmp2 - tmp5);
nuclear@1 269 wsptr[DCTSIZE*4] = (int) (tmp3 + tmp4);
nuclear@1 270 wsptr[DCTSIZE*3] = (int) (tmp3 - tmp4);
nuclear@1 271
nuclear@1 272 inptr++; /* advance pointers to next column */
nuclear@1 273 quantptr++;
nuclear@1 274 wsptr++;
nuclear@1 275 }
nuclear@1 276
nuclear@1 277 /* Pass 2: process rows from work array, store into output array. */
nuclear@1 278 /* Note that we must descale the results by a factor of 8 == 2**3, */
nuclear@1 279 /* and also undo the PASS1_BITS scaling. */
nuclear@1 280
nuclear@1 281 wsptr = workspace;
nuclear@1 282 for (ctr = 0; ctr < DCTSIZE; ctr++) {
nuclear@1 283 outptr = output_buf[ctr] + output_col;
nuclear@1 284 /* Rows of zeroes can be exploited in the same way as we did with columns.
nuclear@1 285 * However, the column calculation has created many nonzero AC terms, so
nuclear@1 286 * the simplification applies less often (typically 5% to 10% of the time).
nuclear@1 287 * On machines with very fast multiplication, it's possible that the
nuclear@1 288 * test takes more time than it's worth. In that case this section
nuclear@1 289 * may be commented out.
nuclear@1 290 */
nuclear@1 291
nuclear@1 292 #ifndef NO_ZERO_ROW_TEST
nuclear@1 293 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
nuclear@1 294 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
nuclear@1 295 /* AC terms all zero */
nuclear@1 296 JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3)
nuclear@1 297 & RANGE_MASK];
nuclear@1 298
nuclear@1 299 outptr[0] = dcval;
nuclear@1 300 outptr[1] = dcval;
nuclear@1 301 outptr[2] = dcval;
nuclear@1 302 outptr[3] = dcval;
nuclear@1 303 outptr[4] = dcval;
nuclear@1 304 outptr[5] = dcval;
nuclear@1 305 outptr[6] = dcval;
nuclear@1 306 outptr[7] = dcval;
nuclear@1 307
nuclear@1 308 wsptr += DCTSIZE; /* advance pointer to next row */
nuclear@1 309 continue;
nuclear@1 310 }
nuclear@1 311 #endif
nuclear@1 312
nuclear@1 313 /* Even part */
nuclear@1 314
nuclear@1 315 tmp10 = ((DCTELEM) wsptr[0] + (DCTELEM) wsptr[4]);
nuclear@1 316 tmp11 = ((DCTELEM) wsptr[0] - (DCTELEM) wsptr[4]);
nuclear@1 317
nuclear@1 318 tmp13 = ((DCTELEM) wsptr[2] + (DCTELEM) wsptr[6]);
nuclear@1 319 tmp12 = MULTIPLY((DCTELEM) wsptr[2] - (DCTELEM) wsptr[6], FIX_1_414213562)
nuclear@1 320 - tmp13;
nuclear@1 321
nuclear@1 322 tmp0 = tmp10 + tmp13;
nuclear@1 323 tmp3 = tmp10 - tmp13;
nuclear@1 324 tmp1 = tmp11 + tmp12;
nuclear@1 325 tmp2 = tmp11 - tmp12;
nuclear@1 326
nuclear@1 327 /* Odd part */
nuclear@1 328
nuclear@1 329 z13 = (DCTELEM) wsptr[5] + (DCTELEM) wsptr[3];
nuclear@1 330 z10 = (DCTELEM) wsptr[5] - (DCTELEM) wsptr[3];
nuclear@1 331 z11 = (DCTELEM) wsptr[1] + (DCTELEM) wsptr[7];
nuclear@1 332 z12 = (DCTELEM) wsptr[1] - (DCTELEM) wsptr[7];
nuclear@1 333
nuclear@1 334 tmp7 = z11 + z13; /* phase 5 */
nuclear@1 335 tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562); /* 2*c4 */
nuclear@1 336
nuclear@1 337 z5 = MULTIPLY(z10 + z12, FIX_1_847759065); /* 2*c2 */
nuclear@1 338 tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5; /* 2*(c2-c6) */
nuclear@1 339 tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5; /* -2*(c2+c6) */
nuclear@1 340
nuclear@1 341 tmp6 = tmp12 - tmp7; /* phase 2 */
nuclear@1 342 tmp5 = tmp11 - tmp6;
nuclear@1 343 tmp4 = tmp10 + tmp5;
nuclear@1 344
nuclear@1 345 /* Final output stage: scale down by a factor of 8 and range-limit */
nuclear@1 346
nuclear@1 347 outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3)
nuclear@1 348 & RANGE_MASK];
nuclear@1 349 outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3)
nuclear@1 350 & RANGE_MASK];
nuclear@1 351 outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3)
nuclear@1 352 & RANGE_MASK];
nuclear@1 353 outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3)
nuclear@1 354 & RANGE_MASK];
nuclear@1 355 outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3)
nuclear@1 356 & RANGE_MASK];
nuclear@1 357 outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3)
nuclear@1 358 & RANGE_MASK];
nuclear@1 359 outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3)
nuclear@1 360 & RANGE_MASK];
nuclear@1 361 outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3)
nuclear@1 362 & RANGE_MASK];
nuclear@1 363
nuclear@1 364 wsptr += DCTSIZE; /* advance pointer to next row */
nuclear@1 365 }
nuclear@1 366 }
nuclear@1 367
nuclear@1 368 #endif /* DCT_IFAST_SUPPORTED */