source: golgotha/src/i4/loaders/jpg/jidctflt.cc @ 80

Last change on this file since 80 was 80, checked in by Sam Hocevar, 12 years ago
  • Adding the Golgotha source code. Not sure what's going to be interesting in there, but since it's all public domain, there's certainly stuff to pick up.
File size: 9.0 KB
Line 
1/********************************************************************** <BR>
2  This file is part of Crack dot Com's free source code release of
3  Golgotha. <a href="http://www.crack.com/golgotha_release"> <BR> for
4  information about compiling & licensing issues visit this URL</a>
5  <PRE> If that doesn't help, contact Jonathan Clark at
6  golgotha_source@usa.net (Subject should have "GOLG" in it)
7***********************************************************************/
8
9/*
10 * jidctflt.c
11 *
12 * Copyright (C) 1994-1996, Thomas G. Lane.
13 * This file is part of the Independent JPEG Group's software.
14 * For conditions of distribution and use, see the accompanying README file.
15 *
16 * This file contains a floating-point implementation of the
17 * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
18 * must also perform dequantization of the input coefficients.
19 *
20 * This implementation should be more accurate than either of the integer
21 * IDCT implementations.  However, it may not give the same results on all
22 * machines because of differences in roundoff behavior.  Speed will depend
23 * on the hardware's floating point capacity.
24 *
25 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
26 * on each row (or vice versa, but it's more convenient to emit a row at
27 * a time).  Direct algorithms are also available, but they are much more
28 * complex and seem not to be any faster when reduced to code.
29 *
30 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
31 * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
32 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
33 * JPEG textbook (see REFERENCES section in file README).  The following code
34 * is based directly on figure 4-8 in P&M.
35 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
36 * possible to arrange the computation so that many of the multiplies are
37 * simple scalings of the final outputs.  These multiplies can then be
38 * folded into the multiplications or divisions by the JPEG quantization
39 * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
40 * to be done in the DCT itself.
41 * The primary disadvantage of this method is that with a fixed-point
42 * implementation, accuracy is lost due to imprecise representation of the
43 * scaled quantization values.  However, that problem does not arise if
44 * we use floating point arithmetic.
45 */
46
47#define JPEG_INTERNALS
48#include "loaders/jpg/jinclude.h"
49#include "loaders/jpg/jpeglib.h"
50#include "loaders/jpg/jdct.h"           /* Private declarations for DCT subsystem */
51
52#ifdef DCT_FLOAT_SUPPORTED
53
54
55/*
56 * This module is specialized to the case DCTSIZE = 8.
57 */
58
59#if DCTSIZE != 8
60  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
61#endif
62
63
64/* Dequantize a coefficient by multiplying it by the multiplier-table
65 * entry; produce a float result.
66 */
67
68#define DEQUANTIZE(coef,quantval)  (((FAST_FLOAT) (coef)) * (quantval))
69
70
71/*
72 * Perform dequantization and inverse DCT on one block of coefficients.
73 */
74
75GLOBAL(void)
76jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
77                 JCOEFPTR coef_block,
78                 JSAMPARRAY output_buf, JDIMENSION output_col)
79{
80  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
81  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
82  FAST_FLOAT z5, z10, z11, z12, z13;
83  JCOEFPTR inptr;
84  FLOAT_MULT_TYPE * quantptr;
85  FAST_FLOAT * wsptr;
86  JSAMPROW outptr;
87  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
88  int ctr;
89  FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
90  SHIFT_TEMPS
91
92  /* Pass 1: process columns from input, store into work array. */
93
94  inptr = coef_block;
95  quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;
96  wsptr = workspace;
97  for (ctr = DCTSIZE; ctr > 0; ctr--) {
98    /* Due to quantization, we will usually find that many of the input
99     * coefficients are zero, especially the AC terms.  We can exploit this
100     * by short-circuiting the IDCT calculation for any column in which all
101     * the AC terms are zero.  In that case each output is equal to the
102     * DC coefficient (with scale factor as needed).
103     * With typical images and quantization tables, half or more of the
104     * column DCT calculations can be simplified this way.
105     */
106   
107    if ((inptr[DCTSIZE*1] | inptr[DCTSIZE*2] | inptr[DCTSIZE*3] |
108         inptr[DCTSIZE*4] | inptr[DCTSIZE*5] | inptr[DCTSIZE*6] |
109         inptr[DCTSIZE*7]) == 0) {
110      /* AC terms all zero */
111      FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
112     
113      wsptr[DCTSIZE*0] = dcval;
114      wsptr[DCTSIZE*1] = dcval;
115      wsptr[DCTSIZE*2] = dcval;
116      wsptr[DCTSIZE*3] = dcval;
117      wsptr[DCTSIZE*4] = dcval;
118      wsptr[DCTSIZE*5] = dcval;
119      wsptr[DCTSIZE*6] = dcval;
120      wsptr[DCTSIZE*7] = dcval;
121     
122      inptr++;                  /* advance pointers to next column */
123      quantptr++;
124      wsptr++;
125      continue;
126    }
127   
128    /* Even part */
129
130    tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
131    tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
132    tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
133    tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
134
135    tmp10 = tmp0 + tmp2;        /* phase 3 */
136    tmp11 = tmp0 - tmp2;
137
138    tmp13 = tmp1 + tmp3;        /* phases 5-3 */
139    tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */
140
141    tmp0 = tmp10 + tmp13;       /* phase 2 */
142    tmp3 = tmp10 - tmp13;
143    tmp1 = tmp11 + tmp12;
144    tmp2 = tmp11 - tmp12;
145   
146    /* Odd part */
147
148    tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
149    tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
150    tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
151    tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
152
153    z13 = tmp6 + tmp5;          /* phase 6 */
154    z10 = tmp6 - tmp5;
155    z11 = tmp4 + tmp7;
156    z12 = tmp4 - tmp7;
157
158    tmp7 = z11 + z13;           /* phase 5 */
159    tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
160
161    z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
162    tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
163    tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
164
165    tmp6 = tmp12 - tmp7;        /* phase 2 */
166    tmp5 = tmp11 - tmp6;
167    tmp4 = tmp10 + tmp5;
168
169    wsptr[DCTSIZE*0] = tmp0 + tmp7;
170    wsptr[DCTSIZE*7] = tmp0 - tmp7;
171    wsptr[DCTSIZE*1] = tmp1 + tmp6;
172    wsptr[DCTSIZE*6] = tmp1 - tmp6;
173    wsptr[DCTSIZE*2] = tmp2 + tmp5;
174    wsptr[DCTSIZE*5] = tmp2 - tmp5;
175    wsptr[DCTSIZE*4] = tmp3 + tmp4;
176    wsptr[DCTSIZE*3] = tmp3 - tmp4;
177
178    inptr++;                    /* advance pointers to next column */
179    quantptr++;
180    wsptr++;
181  }
182 
183  /* Pass 2: process rows from work array, store into output array. */
184  /* Note that we must descale the results by a factor of 8 == 2**3. */
185
186  wsptr = workspace;
187  for (ctr = 0; ctr < DCTSIZE; ctr++) {
188    outptr = output_buf[ctr] + output_col;
189    /* Rows of zeroes can be exploited in the same way as we did with columns.
190     * However, the column calculation has created many nonzero AC terms, so
191     * the simplification applies less often (typically 5% to 10% of the time).
192     * And testing floats for zero is relatively expensive, so we don't bother.
193     */
194   
195    /* Even part */
196
197    tmp10 = wsptr[0] + wsptr[4];
198    tmp11 = wsptr[0] - wsptr[4];
199
200    tmp13 = wsptr[2] + wsptr[6];
201    tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;
202
203    tmp0 = tmp10 + tmp13;
204    tmp3 = tmp10 - tmp13;
205    tmp1 = tmp11 + tmp12;
206    tmp2 = tmp11 - tmp12;
207
208    /* Odd part */
209
210    z13 = wsptr[5] + wsptr[3];
211    z10 = wsptr[5] - wsptr[3];
212    z11 = wsptr[1] + wsptr[7];
213    z12 = wsptr[1] - wsptr[7];
214
215    tmp7 = z11 + z13;
216    tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);
217
218    z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
219    tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
220    tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
221
222    tmp6 = tmp12 - tmp7;
223    tmp5 = tmp11 - tmp6;
224    tmp4 = tmp10 + tmp5;
225
226    /* Final output stage: scale down by a factor of 8 and range-limit */
227
228    outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
229                            & RANGE_MASK];
230    outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
231                            & RANGE_MASK];
232    outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
233                            & RANGE_MASK];
234    outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
235                            & RANGE_MASK];
236    outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
237                            & RANGE_MASK];
238    outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
239                            & RANGE_MASK];
240    outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
241                            & RANGE_MASK];
242    outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
243                            & RANGE_MASK];
244   
245    wsptr += DCTSIZE;           /* advance pointer to next row */
246  }
247}
248
249#endif /* DCT_FLOAT_SUPPORTED */
Note: See TracBrowser for help on using the repository browser.