com32/lib/jpeg/jidctflt.c

   1 /*
   2  * jidctflt.c
   3  *
   4  * Copyright (C) 1994-1998, Thomas G. Lane.
   5  * This file is part of the Independent JPEG Group's software.
   6  *
   7  * The authors make NO WARRANTY or representation, either express or implied,
   8  * with respect to this software, its quality, accuracy, merchantability, or
   9  * fitness for a particular purpose.  This software is provided "AS IS", and you,
  10  * its user, assume the entire risk as to its quality and accuracy.
  11  *
  12  * This software is copyright (C) 1991-1998, Thomas G. Lane.
  13  * All Rights Reserved except as specified below.
  14  *
  15  * Permission is hereby granted to use, copy, modify, and distribute this
  16  * software (or portions thereof) for any purpose, without fee, subject to these
  17  * conditions:
  18  * (1) If any part of the source code for this software is distributed, then this
  19  * README file must be included, with this copyright and no-warranty notice
  20  * unaltered; and any additions, deletions, or changes to the original files
  21  * must be clearly indicated in accompanying documentation.
  22  * (2) If only executable code is distributed, then the accompanying
  23  * documentation must state that "this software is based in part on the work of
  24  * the Independent JPEG Group".
  25  * (3) Permission for use of this software is granted only if the user accepts
  26  * full responsibility for any undesirable consequences; the authors accept
  27  * NO LIABILITY for damages of any kind.
  28  *
  29  * These conditions apply to any software derived from or based on the IJG code,
  30  * not just to the unmodified library.  If you use our work, you ought to
  31  * acknowledge us.
  32  *
  33  * Permission is NOT granted for the use of any IJG author's name or company name
  34  * in advertising or publicity relating to this software or products derived from
  35  * it.  This software may be referred to only as "the Independent JPEG Group's
  36  * software".
  37  *
  38  * We specifically permit and encourage the use of this software as the basis of
  39  * commercial products, provided that all warranty or liability claims are
  40  * assumed by the product vendor.
  41  *
  42  *
  43  * This file contains a floating-point implementation of the
  44  * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
  45  * must also perform dequantization of the input coefficients.
  46  *
  47  * This implementation should be more accurate than either of the integer
  48  * IDCT implementations.  However, it may not give the same results on all
  49  * machines because of differences in roundoff behavior.  Speed will depend
  50  * on the hardware's floating point capacity.
  51  *
  52  * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
  53  * on each row (or vice versa, but it's more convenient to emit a row at
  54  * a time).  Direct algorithms are also available, but they are much more
  55  * complex and seem not to be any faster when reduced to code.
  56  *
  57  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
  58  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  59  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
  60  * JPEG textbook (see REFERENCES section in file README).  The following code
  61  * is based directly on figure 4-8 in P&M.
  62  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  63  * possible to arrange the computation so that many of the multiplies are
  64  * simple scalings of the final outputs.  These multiplies can then be
  65  * folded into the multiplications or divisions by the JPEG quantization
  66  * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
  67  * to be done in the DCT itself.
  68  * The primary disadvantage of this method is that with a fixed-point
  69  * implementation, accuracy is lost due to imprecise representation of the
  70  * scaled quantization values.  However, that problem does not arise if
  71  * we use floating point arithmetic.
  72  */
  73
  74 #include <stdint.h>
  75 #include "tinyjpeg-internal.h"
  76
  77 #define FAST_FLOAT float
  78 #define DCTSIZE    8
  79 #define DCTSIZE2   (DCTSIZE*DCTSIZE)
  80
  81 #define DEQUANTIZE(coef,quantval)  (((FAST_FLOAT) (coef)) * (quantval))
  82
  83 #if defined(__GNUC__) && defined(__i686__) || defined(__x86_64__)
  84
  85 static inline unsigned char descale_and_clamp(int x, int shift)
  86 {
  87   __asm__ (
  88       "add %3,%1\n"
  89       "\tsar %2,%1\n"
  90       "\tsub $-128,%1\n"
  91       "\tcmovl %5,%1\n" /* Use the sub to compare to 0 */
  92       "\tcmpl %4,%1\n"
  93       "\tcmovg %4,%1\n"
  94       : "=r"(x)
  95       : "0"(x), "i"(shift), "i"(1UL<<(shift-1)), "r" (0xff), "r" (0)
  96       );
  97   return x;
  98 }
  99
 100 #else
 101 static inline unsigned char descale_and_clamp(int x, int shift)
 102 {
 103   x += (1UL<<(shift-1));
 104   if (x<0)
 105     x = (x >> shift) | ((~(0UL)) << (32-(shift)));
 106   else
 107     x >>= shift;
 108   x += 128;
 109   if (x>255)
 110     return 255;
 111   else if (x<0)
 112     return 0;
 113   else
 114     return x;
 115 }
 116 #endif
 117
 118 /*
 119  * Perform dequantization and inverse DCT on one block of coefficients.
 120  */
 121
 122 void
 123 jpeg_idct_float (struct component *compptr, uint8_t *output_buf, int stride)
 124 {
 125   FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
 126   FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
 127   FAST_FLOAT z5, z10, z11, z12, z13;
 128   int16_t *inptr;
 129   FAST_FLOAT *quantptr;
 130   FAST_FLOAT *wsptr;
 131   uint8_t *outptr;
 132   int ctr;
 133   FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
 134
 135   /* Pass 1: process columns from input, store into work array. */
 136
 137   inptr = compptr->DCT;
 138   quantptr = compptr->Q_table;
 139   wsptr = workspace;
 140   for (ctr = DCTSIZE; ctr > 0; ctr--) {
 141     /* Due to quantization, we will usually find that many of the input
 142      * coefficients are zero, especially the AC terms.  We can exploit this
 143      * by short-circuiting the IDCT calculation for any column in which all
 144      * the AC terms are zero.  In that case each output is equal to the
 145      * DC coefficient (with scale factor as needed).
 146      * With typical images and quantization tables, half or more of the
 147      * column DCT calculations can be simplified this way.
 148      */
 149
 150     if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
 151         inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
 152         inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
 153         inptr[DCTSIZE*7] == 0) {
 154       /* AC terms all zero */
 155       FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
 156
 157       wsptr[DCTSIZE*0] = dcval;
 158       wsptr[DCTSIZE*1] = dcval;
 159       wsptr[DCTSIZE*2] = dcval;
 160       wsptr[DCTSIZE*3] = dcval;
 161       wsptr[DCTSIZE*4] = dcval;
 162       wsptr[DCTSIZE*5] = dcval;
 163       wsptr[DCTSIZE*6] = dcval;
 164       wsptr[DCTSIZE*7] = dcval;
 165
 166       inptr++;                  /* advance pointers to next column */
 167       quantptr++;
 168       wsptr++;
 169       continue;
 170     }
 171
 172     /* Even part */
 173
 174     tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
 175     tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
 176     tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
 177     tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
 178
 179     tmp10 = tmp0 + tmp2;        /* phase 3 */
 180     tmp11 = tmp0 - tmp2;
 181
 182     tmp13 = tmp1 + tmp3;        /* phases 5-3 */
 183     tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */
 184
 185     tmp0 = tmp10 + tmp13;       /* phase 2 */
 186     tmp3 = tmp10 - tmp13;
 187     tmp1 = tmp11 + tmp12;
 188     tmp2 = tmp11 - tmp12;
 189
 190     /* Odd part */
 191
 192     tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
 193     tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
 194     tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
 195     tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
 196
 197     z13 = tmp6 + tmp5;          /* phase 6 */
 198     z10 = tmp6 - tmp5;
 199     z11 = tmp4 + tmp7;
 200     z12 = tmp4 - tmp7;
 201
 202     tmp7 = z11 + z13;           /* phase 5 */
 203     tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
 204
 205     z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
 206     tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
 207     tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
 208
 209     tmp6 = tmp12 - tmp7;        /* phase 2 */
 210     tmp5 = tmp11 - tmp6;
 211     tmp4 = tmp10 + tmp5;
 212
 213     wsptr[DCTSIZE*0] = tmp0 + tmp7;
 214     wsptr[DCTSIZE*7] = tmp0 - tmp7;
 215     wsptr[DCTSIZE*1] = tmp1 + tmp6;
 216     wsptr[DCTSIZE*6] = tmp1 - tmp6;
 217     wsptr[DCTSIZE*2] = tmp2 + tmp5;
 218     wsptr[DCTSIZE*5] = tmp2 - tmp5;
 219     wsptr[DCTSIZE*4] = tmp3 + tmp4;
 220     wsptr[DCTSIZE*3] = tmp3 - tmp4;
 221
 222     inptr++;                    /* advance pointers to next column */
 223     quantptr++;
 224     wsptr++;
 225   }
 226
 227   /* Pass 2: process rows from work array, store into output array. */
 228   /* Note that we must descale the results by a factor of 8 == 2**3. */
 229
 230   wsptr = workspace;
 231   outptr = output_buf;
 232   for (ctr = 0; ctr < DCTSIZE; ctr++) {
 233     /* Rows of zeroes can be exploited in the same way as we did with columns.
 234      * However, the column calculation has created many nonzero AC terms, so
 235      * the simplification applies less often (typically 5% to 10% of the time).
 236      * And testing floats for zero is relatively expensive, so we don't bother.
 237      */
 238
 239     /* Even part */
 240
 241     tmp10 = wsptr[0] + wsptr[4];
 242     tmp11 = wsptr[0] - wsptr[4];
 243
 244     tmp13 = wsptr[2] + wsptr[6];
 245     tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;
 246
 247     tmp0 = tmp10 + tmp13;
 248     tmp3 = tmp10 - tmp13;
 249     tmp1 = tmp11 + tmp12;
 250     tmp2 = tmp11 - tmp12;
 251
 252     /* Odd part */
 253
 254     z13 = wsptr[5] + wsptr[3];
 255     z10 = wsptr[5] - wsptr[3];
 256     z11 = wsptr[1] + wsptr[7];
 257     z12 = wsptr[1] - wsptr[7];
 258
 259     tmp7 = z11 + z13;
 260     tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);
 261
 262     z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
 263     tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
 264     tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
 265
 266     tmp6 = tmp12 - tmp7;
 267     tmp5 = tmp11 - tmp6;
 268     tmp4 = tmp10 + tmp5;
 269
 270     /* Final output stage: scale down by a factor of 8 and range-limit */
 271
 272     outptr[0] = descale_and_clamp(tmp0 + tmp7, 3);
 273     outptr[7] = descale_and_clamp(tmp0 - tmp7, 3);
 274     outptr[1] = descale_and_clamp(tmp1 + tmp6, 3);
 275     outptr[6] = descale_and_clamp(tmp1 - tmp6, 3);
 276     outptr[2] = descale_and_clamp(tmp2 + tmp5, 3);
 277     outptr[5] = descale_and_clamp(tmp2 - tmp5, 3);
 278     outptr[4] = descale_and_clamp(tmp3 + tmp4, 3);
 279     outptr[3] = descale_and_clamp(tmp3 - tmp4, 3);
 280
 281
 282     wsptr += DCTSIZE;           /* advance pointer to next row */
 283     outptr += stride;
 284   }
 285 }