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77 //<MStar Software>
78 /*
79 * jidctfst.c
80 *
81 * Copyright (C) 1994-1998, Thomas G. Lane.
82 * This file is part of the Independent JPEG Group's software.
83 * For conditions of distribution and use, see the accompanying README file.
84 *
85 * This file contains a fast, not so accurate integer implementation of the
86 * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
87 * must also perform dequantization of the input coefficients.
88 *
89 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
90 * on each row (or vice versa, but it's more convenient to emit a row at
91 * a time). Direct algorithms are also available, but they are much more
92 * complex and seem not to be any faster when reduced to code.
93 *
94 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
95 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
96 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
97 * JPEG textbook (see REFERENCES section in file README). The following code
98 * is based directly on figure 4-8 in P&M.
99 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
100 * possible to arrange the computation so that many of the multiplies are
101 * simple scalings of the final outputs. These multiplies can then be
102 * folded into the multiplications or divisions by the JPEG quantization
103 * table entries. The AA&N method leaves only 5 multiplies and 29 adds
104 * to be done in the DCT itself.
105 * The primary disadvantage of this method is that with fixed-point math,
106 * accuracy is lost due to imprecise representation of the scaled
107 * quantization values. The smaller the quantization table entry, the less
108 * precise the scaled value, so this implementation does worse with high-
109 * quality-setting files than with low-quality ones.
110 */
111
112 ///#define JPEG_INTERNALS
113 ///#include "jinclude.h"
114 ///#include "jpeglib.h"
115 ///#include "jdct.h" /* Private declarations for DCT subsystem */
116 #include "jpegmain.h"
117 #include "apiJPEG.h"
118
119 #define DCTSIZE 8
120 #define BITS_IN_JSAMPLE 8
121 #define DCT_IFAST_SUPPORTED
122
123 #ifdef DCT_IFAST_SUPPORTED
124
125 /*
126 * This module is specialized to the case DCTSIZE = 8.
127 */
128
129 #if DCTSIZE != 8
130 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
131 #endif
132
133
134 /* Scaling decisions are generally the same as in the LL&M algorithm;
135 * see jidctint.c for more details. However, we choose to descale
136 * (right shift) multiplication products as soon as they are formed,
137 * rather than carrying additional fractional bits into subsequent additions.
138 * This compromises accuracy slightly, but it lets us save a few shifts.
139 * More importantly, 16-bit arithmetic is then adequate (for 8-bit samples)
140 * everywhere except in the multiplications proper; this saves a good deal
141 * of work on 16-bit-int machines.
142 *
143 * The dequantized coefficients are not integers because the AA&N scaling
144 * factors have been incorporated. We represent them scaled up by PASS1_BITS,
145 * so that the first and second IDCT rounds have the same input scaling.
146 * For 8-bit JSAMPLEs, we choose IFAST_SCALE_BITS = PASS1_BITS so as to
147 * avoid a descaling shift; this compromises accuracy rather drastically
148 * for small quantization table entries, but it saves a lot of shifts.
149 * For 12-bit JSAMPLEs, there's no hope of using 16x16 multiplies anyway,
150 * so we use a much larger scaling factor to preserve accuracy.
151 *
152 * A final compromise is to represent the multiplicative constants to only
153 * 8 fractional bits, rather than 13. This saves some shifting work on some
154 * machines, and may also reduce the cost of multiplication (since there
155 * are fewer one-bits in the constants).
156 */
157
158 #if BITS_IN_JSAMPLE == 8
159 #define CONST_BITS 8
160 #define PASS1_BITS 2
161 #else
162 #define CONST_BITS 8
163 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */
164 #endif
165
166 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
167 * causing a lot of useless floating-point operations at run time.
168 * To get around this we use the following pre-calculated constants.
169 * If you change CONST_BITS you may want to add appropriate values.
170 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
171 */
172
173 #if CONST_BITS == 8
174 #define FIX_1_082392200 ((INT32) 277) /* FIX(1.082392200) */
175 #define FIX_1_414213562 ((INT32) 362) /* FIX(1.414213562) */
176 #define FIX_1_847759065 ((INT32) 473) /* FIX(1.847759065) */
177 #define FIX_2_613125930 ((INT32) 669) /* FIX(2.613125930) */
178 #else
179 #define FIX_1_082392200 FIX(1.082392200)
180 #define FIX_1_414213562 FIX(1.414213562)
181 #define FIX_1_847759065 FIX(1.847759065)
182 #define FIX_2_613125930 FIX(2.613125930)
183 #endif
184
185
186 /* We can gain a little more speed, with a further compromise in accuracy,
187 * by omitting the addition in a descaling shift. This yields an incorrectly
188 * rounded result half the time...
189 */
190
191 #ifndef USE_ACCURATE_ROUNDING
192 #undef DESCALE
193 //#define DESCALE(x,n) RIGHT_SHIFT(x, n)
194 #define DESCALE(x,n) ((x) >> (n)) //=> speed a little with a compromise in accuracy
195 //#define DESCALE(x,n) (((x) + ( ((int32)1) << ((n)-1))) >> (n)) //
196 #endif
197
198
199 /* Multiply a DCTELEM variable by an INT32 constant, and immediately
200 * descale to yield a DCTELEM result.
201 */
202
203 typedef int DCTELEM; /* 16 or 32 bits is fine */
204 #define MULTIPLY(var,cnst) ((DCTELEM) DESCALE((var) * (cnst), CONST_BITS))
205
206
207 /* Dequantize a coefficient by multiplying it by the multiplier-table
208 * entry; produce a DCTELEM result. For 8-bit data a 16x16->16
209 * multiplication will do. For 12-bit data, the multiplier table is
210 * declared INT32, so a 32-bit multiply will be used.
211 */
212
213 #if BITS_IN_JSAMPLE == 8
214 //#define DEQUANTIZE(coef,quantval) (((IFAST_MULT_TYPE) (coef)) * (quantval))
215 #define DEQUANTIZE(coef,quantval) (coef)
216 #else
217 #define DEQUANTIZE(coef,quantval) \
218 DESCALE((coef)*(quantval), IFAST_SCALE_BITS-PASS1_BITS)
219 #endif
220
221
222 /* Like DESCALE, but applies to a DCTELEM and produces an int.
223 * We assume that int right shift is unsigned if INT32 right shift is.
224 */
225
226 #ifdef RIGHT_SHIFT_IS_UNSIGNED
227 #define ISHIFT_TEMPS DCTELEM ishift_temp;
228 #if BITS_IN_JSAMPLE == 8
229 #define DCTELEMBITS 16 /* DCTELEM may be 16 or 32 bits */
230 #else
231 #define DCTELEMBITS 32 /* DCTELEM must be 32 bits */
232 #endif
233 #define IRIGHT_SHIFT(x,shft) \
234 ((ishift_temp = (x)) < 0 ? \
235 (ishift_temp >> (shft)) | ((~((DCTELEM) 0)) << (DCTELEMBITS-(shft))) : \
236 (ishift_temp >> (shft)))
237 #else
238 #define ISHIFT_TEMPS
239 #define IRIGHT_SHIFT(x,shft) ((x) >> (shft))
240 #endif
241
242 #if 1///def USE_ACCURATE_ROUNDING
243 #define IDESCALE(x,n) ((int) IRIGHT_SHIFT((x) + (1 << ((n)-1)), n))
244 //#define IDESCALE(x,n) ( ( (int)(x) + (1 << ((n)-1)) ) >> (n) )
245 #else
246 #define IDESCALE(x,n) ((int) IRIGHT_SHIFT(x, n))
247 #endif
248
249 #define IFAST_MULT_TYPE int
250
251 #define clamp(i) if (i & 0xFF00) i = (((~i) >> 15) & 0xFF);
252
253 /*
254 * Perform dequantization and inverse DCT on one block of coefficients.
255 */
256
257 ///GLOBAL(void)
258 ///jpeg_idct_ifast (j_decompress_ptr cinfo, jpeg_component_info * compptr,
259 /// JCOEFPTR coef_block,
260 /// JSAMPARRAY output_buf, JDIMENSION output_col)
jpeg_idct_ifast(JPEG_BLOCK_TYPE * data,U8 * Pdst_ptr)261 void jpeg_idct_ifast( JPEG_BLOCK_TYPE *data, U8 *Pdst_ptr )
262 {
263 #define INT32 S32
264 #define DCTSIZE2 64
265 #define DCTSIZE 8
266
267 DCTELEM tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
268 DCTELEM tmp10, tmp11, tmp12, tmp13;
269 DCTELEM z5, z10, z11, z12, z13;
270 ///JCOEFPTR inptr;
271 register JPEG_BLOCK_TYPE *inptr;
272 IFAST_MULT_TYPE *quantptr;
273 ///JSAMPROW outptr;
274 U8 *outptr = Pdst_ptr;
275 ///JSAMPLE *range_limit = IDCT_range_limit(cinfo);
276 int ctr;
277 ///int workspace[DCTSIZE2]; /* buffers data between passes */
278 JPEG_BLOCK_TYPE workspace[DCTSIZE2];
279 JPEG_BLOCK_TYPE *wsptr;
280 ///SHIFT_TEMPS /* for DESCALE */
281 ///ISHIFT_TEMPS /* for IDESCALE */
282 S16 i;
283 //printf("jidctfst::jpeg_idct_ifast\n");
284 /* Pass 1: process columns from input, store into work array. */
285
286 inptr = data;
287 ///quantptr = (IFAST_MULT_TYPE *) compptr->dct_table;
288 wsptr = workspace;
289 for ( ctr = DCTSIZE; ctr > 0; ctr-- )
290 {
291 /* Due to quantization, we will usually find that many of the input
292 * coefficients are zero, especially the AC terms. We can exploit this
293 * by short-circuiting the IDCT calculation for any column in which all
294 * the AC terms are zero. In that case each output is equal to the
295 * DC coefficient (with scale factor as needed).
296 * With typical images and quantization tables, half or more of the
297 * column DCT calculations can be simplified this way.
298 */
299
300 if ( inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 && inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 4] == 0 && inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 6] == 0 && inptr[DCTSIZE * 7] == 0 )
301 {
302 /* AC terms all zero */
303 int dcval = ( int )DEQUANTIZE( inptr[DCTSIZE*0], quantptr[DCTSIZE*0] );
304
305 wsptr[DCTSIZE * 0] = dcval;
306 wsptr[DCTSIZE * 1] = dcval;
307 wsptr[DCTSIZE * 2] = dcval;
308 wsptr[DCTSIZE * 3] = dcval;
309 wsptr[DCTSIZE * 4] = dcval;
310 wsptr[DCTSIZE * 5] = dcval;
311 wsptr[DCTSIZE * 6] = dcval;
312 wsptr[DCTSIZE * 7] = dcval;
313
314 inptr++; /* advance pointers to next column */
315 quantptr++;
316 wsptr++;
317 continue;
318 }
319
320 /* Even part */
321
322 tmp0 = DEQUANTIZE( inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0] );
323 tmp1 = DEQUANTIZE( inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2] );
324 tmp2 = DEQUANTIZE( inptr[DCTSIZE * 4], quantptr[DCTSIZE * 4] );
325 tmp3 = DEQUANTIZE( inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6] );
326
327 tmp10 = tmp0 + tmp2; /* phase 3 */
328 tmp11 = tmp0 - tmp2;
329
330 tmp13 = tmp1 + tmp3; /* phases 5-3 */
331 tmp12 = MULTIPLY( tmp1 - tmp3, FIX_1_414213562 ) - tmp13; /* 2*c4 */
332
333 tmp0 = tmp10 + tmp13; /* phase 2 */
334 tmp3 = tmp10 - tmp13;
335 tmp1 = tmp11 + tmp12;
336 tmp2 = tmp11 - tmp12;
337
338 /* Odd part */
339
340 tmp4 = DEQUANTIZE( inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1] );
341 tmp5 = DEQUANTIZE( inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3] );
342 tmp6 = DEQUANTIZE( inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5] );
343 tmp7 = DEQUANTIZE( inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7] );
344
345 z13 = tmp6 + tmp5; /* phase 6 */
346 z10 = tmp6 - tmp5;
347 z11 = tmp4 + tmp7;
348 z12 = tmp4 - tmp7;
349
350 tmp7 = z11 + z13; /* phase 5 */
351 tmp11 = MULTIPLY( z11 - z13, FIX_1_414213562 ); /* 2*c4 */
352
353 z5 = MULTIPLY( z10 + z12, FIX_1_847759065 ); /* 2*c2 */
354 tmp10 = MULTIPLY( z12, FIX_1_082392200 ) - z5; /* 2*(c2-c6) */
355 tmp12 = MULTIPLY( z10, -FIX_2_613125930 ) + z5; /* -2*(c2+c6) */
356
357 tmp6 = tmp12 - tmp7; /* phase 2 */
358 tmp5 = tmp11 - tmp6;
359 tmp4 = tmp10 + tmp5;
360
361 wsptr[DCTSIZE * 0] = ( int )( tmp0 + tmp7 );
362 wsptr[DCTSIZE * 7] = ( int )( tmp0 - tmp7 );
363 wsptr[DCTSIZE * 1] = ( int )( tmp1 + tmp6 );
364 wsptr[DCTSIZE * 6] = ( int )( tmp1 - tmp6 );
365 wsptr[DCTSIZE * 2] = ( int )( tmp2 + tmp5 );
366 wsptr[DCTSIZE * 5] = ( int )( tmp2 - tmp5 );
367 wsptr[DCTSIZE * 4] = ( int )( tmp3 + tmp4 );
368 wsptr[DCTSIZE * 3] = ( int )( tmp3 - tmp4 );
369
370 inptr++; /* advance pointers to next column */
371 quantptr++;
372 wsptr++;
373 }
374
375 /* Pass 2: process rows from work array, store into output array. */
376 /* Note that we must descale the results by a factor of 8 == 2**3, */
377 /* and also undo the PASS1_BITS scaling. */
378
379 wsptr = workspace;
380 for ( ctr = 0; ctr < DCTSIZE; ctr++ )
381 {
382 ///outptr = output_buf[ctr] + output_col;
383 /* Rows of zeroes can be exploited in the same way as we did with columns.
384 * However, the column calculation has created many nonzero AC terms, so
385 * the simplification applies less often (typically 5% to 10% of the time).
386 * On machines with very fast multiplication, it's possible that the
387 * test takes more time than it's worth. In that case this section
388 * may be commented out.
389 */
390
391 #if 1///ndef NO_ZERO_ROW_TEST
392 if ( wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 && wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0 )
393 {
394 /* AC terms all zero */
395 //JSAMPLE dcval = range_limit[IDESCALE(wsptr[0], PASS1_BITS+3) & RANGE_MASK];
396 int dcval = IDESCALE( wsptr[0], PASS1_BITS + 3 ) + 128;
397 clamp( dcval );
398
399 outptr[0] = dcval;
400 outptr[1] = dcval;
401 outptr[2] = dcval;
402 outptr[3] = dcval;
403 outptr[4] = dcval;
404 outptr[5] = dcval;
405 outptr[6] = dcval;
406 outptr[7] = dcval;
407
408 wsptr += DCTSIZE; /* advance pointer to next row */
409 outptr += DCTSIZE;
410 continue;
411 }
412 #endif
413
414 /* Even part */
415
416 tmp10 = ( ( DCTELEM )wsptr[0] + ( DCTELEM )wsptr[4] );
417 tmp11 = ( ( DCTELEM )wsptr[0] - ( DCTELEM )wsptr[4] );
418
419 tmp13 = ( ( DCTELEM )wsptr[2] + ( DCTELEM )wsptr[6] );
420 tmp12 = MULTIPLY( ( DCTELEM )wsptr[2] - ( DCTELEM )wsptr[6], FIX_1_414213562 ) - tmp13;
421
422 tmp0 = tmp10 + tmp13;
423 tmp3 = tmp10 - tmp13;
424 tmp1 = tmp11 + tmp12;
425 tmp2 = tmp11 - tmp12;
426
427 /* Odd part */
428
429 z13 = ( DCTELEM )wsptr[5] + ( DCTELEM )wsptr[3];
430 z10 = ( DCTELEM )wsptr[5] - ( DCTELEM )wsptr[3];
431 z11 = ( DCTELEM )wsptr[1] + ( DCTELEM )wsptr[7];
432 z12 = ( DCTELEM )wsptr[1] - ( DCTELEM )wsptr[7];
433
434 tmp7 = z11 + z13; /* phase 5 */
435 tmp11 = MULTIPLY( z11 - z13, FIX_1_414213562 ); /* 2*c4 */
436
437 z5 = MULTIPLY( z10 + z12, FIX_1_847759065 ); /* 2*c2 */
438 tmp10 = MULTIPLY( z12, FIX_1_082392200 ) - z5; /* 2*(c2-c6) */
439 tmp12 = MULTIPLY( z10, -FIX_2_613125930 ) + z5; /* -2*(c2+c6) */
440
441 tmp6 = tmp12 - tmp7; /* phase 2 */
442 tmp5 = tmp11 - tmp6;
443 tmp4 = tmp10 + tmp5;
444
445 /* Final output stage: scale down by a factor of 8 and range-limit */
446 /*
447 outptr[0] = range_limit[IDESCALE(tmp0 + tmp7, PASS1_BITS+3)
448 & RANGE_MASK];
449 outptr[7] = range_limit[IDESCALE(tmp0 - tmp7, PASS1_BITS+3)
450 & RANGE_MASK];
451 outptr[1] = range_limit[IDESCALE(tmp1 + tmp6, PASS1_BITS+3)
452 & RANGE_MASK];
453 outptr[6] = range_limit[IDESCALE(tmp1 - tmp6, PASS1_BITS+3)
454 & RANGE_MASK];
455 outptr[2] = range_limit[IDESCALE(tmp2 + tmp5, PASS1_BITS+3)
456 & RANGE_MASK];
457 outptr[5] = range_limit[IDESCALE(tmp2 - tmp5, PASS1_BITS+3)
458 & RANGE_MASK];
459 outptr[4] = range_limit[IDESCALE(tmp3 + tmp4, PASS1_BITS+3)
460 & RANGE_MASK];
461 outptr[3] = range_limit[IDESCALE(tmp3 - tmp4, PASS1_BITS+3)
462 & RANGE_MASK];
463 */
464 i = IDESCALE( tmp0 + tmp7, PASS1_BITS + 3 ) + 128;
465 clamp( i );
466 outptr[0] = ( U8 )i;
467 i = IDESCALE( tmp0 - tmp7, PASS1_BITS + 3 ) + 128;
468 clamp( i );
469 outptr[7] = ( U8 )i;
470 i = IDESCALE( tmp1 + tmp6, PASS1_BITS + 3 ) + 128;
471 clamp( i );
472 outptr[1] = ( U8 )i;
473 i = IDESCALE( tmp1 - tmp6, PASS1_BITS + 3 ) + 128;
474 clamp( i );
475 outptr[6] = ( U8 )i;
476 i = IDESCALE( tmp2 + tmp5, PASS1_BITS + 3 ) + 128;
477 clamp( i );
478 outptr[2] = ( U8 )i;
479 i = IDESCALE( tmp2 - tmp5, PASS1_BITS + 3 ) + 128;
480 clamp( i );
481 outptr[5] = ( U8 )i;
482 i = IDESCALE( tmp3 + tmp4, PASS1_BITS + 3 ) + 128;
483 clamp( i );
484 outptr[4] = ( U8 )i;
485 i = IDESCALE( tmp3 - tmp4, PASS1_BITS + 3 ) + 128;
486 clamp( i );
487 outptr[3] = ( U8 )i;
488
489 wsptr += DCTSIZE; /* advance pointer to next row */
490 outptr += DCTSIZE;
491 }
492 }
493
494 #endif /* DCT_IFAST_SUPPORTED */
495