/src/gdal/build/frmts/jpeg/libjpeg12/jidctflt12.c

Source (jump to first uncovered line)
/*
 * jidctflt.c
 *
 * Copyright (C) 1994-1998, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains a floating-point implementation of the
 * inverse DCT (Discrete Cosine Transform).  In the IJG code, this routine
 * must also perform dequantization of the input coefficients.
 *
 * This implementation should be more accurate than either of the integer
 * IDCT implementations.  However, it may not give the same results on all
 * machines because of differences in roundoff behavior.  Speed will depend
 * on the hardware's floating point capacity.
 *
 * A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
 * on each row (or vice versa, but it's more convenient to emit a row at
 * a time).  Direct algorithms are also available, but they are much more
 * complex and seem not to be any faster when reduced to code.
 *
 * This implementation is based on Arai, Agui, and Nakajima's algorithm for
 * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
 * Japanese, but the algorithm is described in the Pennebaker & Mitchell
 * JPEG textbook (see REFERENCES section in file README).  The following code
 * is based directly on figure 4-8 in P&M.
 * While an 8-point DCT cannot be done in less than 11 multiplies, it is
 * possible to arrange the computation so that many of the multiplies are
 * simple scalings of the final outputs.  These multiplies can then be
 * folded into the multiplications or divisions by the JPEG quantization
 * table entries.  The AA&N method leaves only 5 multiplies and 29 adds
 * to be done in the DCT itself.
 * The primary disadvantage of this method is that with a fixed-point
 * implementation, accuracy is lost due to imprecise representation of the
 * scaled quantization values.  However, that problem does not arise if
 * we use floating point arithmetic.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"   /* Private declarations for DCT subsystem */

#ifdef DCT_FLOAT_SUPPORTED


/*
 * This module is specialized to the case DCTSIZE = 8.
 */

#if DCTSIZE != 8
  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
#endif


/* Dequantize a coefficient by multiplying it by the multiplier-table
 * entry; produce a float result.
 */

#define DEQUANTIZE(coef,quantval)  (((FAST_FLOAT) (coef)) * (quantval))


/*
 * Perform dequantization and inverse DCT on one block of coefficients.
 */

GLOBAL(void)
jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
     JCOEFPTR coef_block,
     JSAMPARRAY output_buf, JDIMENSION output_col)
{
  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
  FAST_FLOAT z5, z10, z11, z12, z13;
  JCOEFPTR inptr;
  FLOAT_MULT_TYPE * quantptr;
  FAST_FLOAT * wsptr;
  JSAMPROW outptr;
  JSAMPLE *range_limit = IDCT_range_limit(cinfo);
  int ctr;
  FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
  SHIFT_TEMPS

  /* Pass 1: process columns from input, store into work array. */

  inptr = coef_block;
  quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;
  wsptr = workspace;
  for (ctr = DCTSIZE; ctr > 0; ctr--) {
    /* Due to quantization, we will usually find that many of the input
     * coefficients are zero, especially the AC terms.  We can exploit this
     * by short-circuiting the IDCT calculation for any column in which all
     * the AC terms are zero.  In that case each output is equal to the
     * DC coefficient (with scale factor as needed).
     * With typical images and quantization tables, half or more of the
     * column DCT calculations can be simplified this way.
     */
    
    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) {
      /* AC terms all zero */
      FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
      
      wsptr[DCTSIZE*0] = dcval;
      wsptr[DCTSIZE*1] = dcval;
      wsptr[DCTSIZE*2] = dcval;
      wsptr[DCTSIZE*3] = dcval;
      wsptr[DCTSIZE*4] = dcval;
      wsptr[DCTSIZE*5] = dcval;
      wsptr[DCTSIZE*6] = dcval;
      wsptr[DCTSIZE*7] = dcval;
      
      inptr++;      /* advance pointers to next column */
      quantptr++;
      wsptr++;
      continue;
    }
    
    /* Even part */

    tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
    tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
    tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
    tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);

    tmp10 = tmp0 + tmp2;  /* phase 3 */
    tmp11 = tmp0 - tmp2;

    tmp13 = tmp1 + tmp3;  /* phases 5-3 */
    tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */

    tmp0 = tmp10 + tmp13; /* phase 2 */
    tmp3 = tmp10 - tmp13;
    tmp1 = tmp11 + tmp12;
    tmp2 = tmp11 - tmp12;
    
    /* Odd part */

    tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
    tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
    tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
    tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);

    z13 = tmp6 + tmp5;    /* phase 6 */
    z10 = tmp6 - tmp5;
    z11 = tmp4 + tmp7;
    z12 = tmp4 - tmp7;

    tmp7 = z11 + z13;   /* phase 5 */
    tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */

    z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
    tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
    tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */

    tmp6 = tmp12 - tmp7;  /* phase 2 */
    tmp5 = tmp11 - tmp6;
    tmp4 = tmp10 + tmp5;

    wsptr[DCTSIZE*0] = tmp0 + tmp7;
    wsptr[DCTSIZE*7] = tmp0 - tmp7;
    wsptr[DCTSIZE*1] = tmp1 + tmp6;
    wsptr[DCTSIZE*6] = tmp1 - tmp6;
    wsptr[DCTSIZE*2] = tmp2 + tmp5;
    wsptr[DCTSIZE*5] = tmp2 - tmp5;
    wsptr[DCTSIZE*4] = tmp3 + tmp4;
    wsptr[DCTSIZE*3] = tmp3 - tmp4;

    inptr++;      /* advance pointers to next column */
    quantptr++;
    wsptr++;
  }
  
  /* Pass 2: process rows from work array, store into output array. */
  /* Note that we must descale the results by a factor of 8 == 2**3. */

  wsptr = workspace;
  for (ctr = 0; ctr < DCTSIZE; ctr++) {
    outptr = output_buf[ctr] + output_col;
    /* Rows of zeroes can be exploited in the same way as we did with columns.
     * However, the column calculation has created many nonzero AC terms, so
     * the simplification applies less often (typically 5% to 10% of the time).
     * And testing floats for zero is relatively expensive, so we don't bother.
     */
    
    /* Even part */

    tmp10 = wsptr[0] + wsptr[4];
    tmp11 = wsptr[0] - wsptr[4];

    tmp13 = wsptr[2] + wsptr[6];
    tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;

    tmp0 = tmp10 + tmp13;
    tmp3 = tmp10 - tmp13;
    tmp1 = tmp11 + tmp12;
    tmp2 = tmp11 - tmp12;

    /* Odd part */

    z13 = wsptr[5] + wsptr[3];
    z10 = wsptr[5] - wsptr[3];
    z11 = wsptr[1] + wsptr[7];
    z12 = wsptr[1] - wsptr[7];

    tmp7 = z11 + z13;
    tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);

    z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
    tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
    tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */

    tmp6 = tmp12 - tmp7;
    tmp5 = tmp11 - tmp6;
    tmp4 = tmp10 + tmp5;

    /* Final output stage: scale down by a factor of 8 and range-limit */

    outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
          & RANGE_MASK];
    outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
          & RANGE_MASK];
    outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
          & RANGE_MASK];
    outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
          & RANGE_MASK];
    outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
          & RANGE_MASK];
    outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
          & RANGE_MASK];
    outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
          & RANGE_MASK];
    outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
          & RANGE_MASK];
    
    wsptr += DCTSIZE;   /* advance pointer to next row */
  }
}

#endif /* DCT_FLOAT_SUPPORTED */

Coverage Report

Created: 2025-06-13 06:18

Line	Count	Source (jump to first uncovered line)
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		* For conditions of distribution and use, see the accompanying README file.
7		*
8		* This file contains a floating-point implementation of the
9		* inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
10		* must also perform dequantization of the input coefficients.
11		*
12		* This implementation should be more accurate than either of the integer
13		* IDCT implementations. However, it may not give the same results on all
14		* machines because of differences in roundoff behavior. Speed will depend
15		* on the hardware's floating point capacity.
16		*
17		* A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
18		* on each row (or vice versa, but it's more convenient to emit a row at
19		* a time). Direct algorithms are also available, but they are much more
20		* complex and seem not to be any faster when reduced to code.
21		*
22		* This implementation is based on Arai, Agui, and Nakajima's algorithm for
23		* scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
24		* Japanese, but the algorithm is described in the Pennebaker & Mitchell
25		* JPEG textbook (see REFERENCES section in file README). The following code
26		* is based directly on figure 4-8 in P&M.
27		* While an 8-point DCT cannot be done in less than 11 multiplies, it is
28		* possible to arrange the computation so that many of the multiplies are
29		* simple scalings of the final outputs. These multiplies can then be
30		* folded into the multiplications or divisions by the JPEG quantization
31		* table entries. The AA&N method leaves only 5 multiplies and 29 adds
32		* to be done in the DCT itself.
33		* The primary disadvantage of this method is that with a fixed-point
34		* implementation, accuracy is lost due to imprecise representation of the
35		* scaled quantization values. However, that problem does not arise if
36		* we use floating point arithmetic.
37		*/
38
39		#define JPEG_INTERNALS
40		#include "jinclude.h"
41		#include "jpeglib.h"
42		#include "jdct.h" /* Private declarations for DCT subsystem */
43
44		#ifdef DCT_FLOAT_SUPPORTED
45
46
47		/*
48		* This module is specialized to the case DCTSIZE = 8.
49		*/
50
51		#if DCTSIZE != 8
52		Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
53		#endif
54
55
56		/* Dequantize a coefficient by multiplying it by the multiplier-table
57		* entry; produce a float result.
58		*/
59
60	0	#define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval))
61
62
63		/*
64		* Perform dequantization and inverse DCT on one block of coefficients.
65		*/
66
67		GLOBAL(void)
68		jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
69		JCOEFPTR coef_block,
70		JSAMPARRAY output_buf, JDIMENSION output_col)
71	0	{
72	0	FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
73	0	FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
74	0	FAST_FLOAT z5, z10, z11, z12, z13;
75	0	JCOEFPTR inptr;
76	0	FLOAT_MULT_TYPE * quantptr;
77	0	FAST_FLOAT * wsptr;
78	0	JSAMPROW outptr;
79	0	JSAMPLE *range_limit = IDCT_range_limit(cinfo);
80	0	int ctr;
81	0	FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
82		SHIFT_TEMPS
83
84		/* Pass 1: process columns from input, store into work array. */
85
86	0	inptr = coef_block;
87	0	quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;
88	0	wsptr = workspace;
89	0	for (ctr = DCTSIZE; ctr > 0; ctr--) {
90		/* Due to quantization, we will usually find that many of the input
91		* coefficients are zero, especially the AC terms. We can exploit this
92		* by short-circuiting the IDCT calculation for any column in which all
93		* the AC terms are zero. In that case each output is equal to the
94		* DC coefficient (with scale factor as needed).
95		* With typical images and quantization tables, half or more of the
96		* column DCT calculations can be simplified this way.
97		*/
98
99	0	if (inptr[DCTSIZE1] == 0 && inptr[DCTSIZE2] == 0 &&
100	0	inptr[DCTSIZE3] == 0 && inptr[DCTSIZE4] == 0 &&
101	0	inptr[DCTSIZE5] == 0 && inptr[DCTSIZE6] == 0 &&
102	0	inptr[DCTSIZE*7] == 0) {
103		/* AC terms all zero */
104	0	FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE0], quantptr[DCTSIZE0]);
105
106	0	wsptr[DCTSIZE*0] = dcval;
107	0	wsptr[DCTSIZE*1] = dcval;
108	0	wsptr[DCTSIZE*2] = dcval;
109	0	wsptr[DCTSIZE*3] = dcval;
110	0	wsptr[DCTSIZE*4] = dcval;
111	0	wsptr[DCTSIZE*5] = dcval;
112	0	wsptr[DCTSIZE*6] = dcval;
113	0	wsptr[DCTSIZE*7] = dcval;
114
115	0	inptr++; /* advance pointers to next column */
116	0	quantptr++;
117	0	wsptr++;
118	0	continue;
119	0	}
120
121		/* Even part */
122
123	0	tmp0 = DEQUANTIZE(inptr[DCTSIZE0], quantptr[DCTSIZE0]);
124	0	tmp1 = DEQUANTIZE(inptr[DCTSIZE2], quantptr[DCTSIZE2]);
125	0	tmp2 = DEQUANTIZE(inptr[DCTSIZE4], quantptr[DCTSIZE4]);
126	0	tmp3 = DEQUANTIZE(inptr[DCTSIZE6], quantptr[DCTSIZE6]);
127
128	0	tmp10 = tmp0 + tmp2; /* phase 3 */
129	0	tmp11 = tmp0 - tmp2;
130
131	0	tmp13 = tmp1 + tmp3; /* phases 5-3 */
132	0	tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2c4 /
133
134	0	tmp0 = tmp10 + tmp13; /* phase 2 */
135	0	tmp3 = tmp10 - tmp13;
136	0	tmp1 = tmp11 + tmp12;
137	0	tmp2 = tmp11 - tmp12;
138
139		/* Odd part */
140
141	0	tmp4 = DEQUANTIZE(inptr[DCTSIZE1], quantptr[DCTSIZE1]);
142	0	tmp5 = DEQUANTIZE(inptr[DCTSIZE3], quantptr[DCTSIZE3]);
143	0	tmp6 = DEQUANTIZE(inptr[DCTSIZE5], quantptr[DCTSIZE5]);
144	0	tmp7 = DEQUANTIZE(inptr[DCTSIZE7], quantptr[DCTSIZE7]);
145
146	0	z13 = tmp6 + tmp5; /* phase 6 */
147	0	z10 = tmp6 - tmp5;
148	0	z11 = tmp4 + tmp7;
149	0	z12 = tmp4 - tmp7;
150
151	0	tmp7 = z11 + z13; /* phase 5 */
152	0	tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2c4 /
153
154	0	z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2c2 /
155	0	tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2(c2-c6) /
156	0	tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2(c2+c6) /
157
158	0	tmp6 = tmp12 - tmp7; /* phase 2 */
159	0	tmp5 = tmp11 - tmp6;
160	0	tmp4 = tmp10 + tmp5;
161
162	0	wsptr[DCTSIZE*0] = tmp0 + tmp7;
163	0	wsptr[DCTSIZE*7] = tmp0 - tmp7;
164	0	wsptr[DCTSIZE*1] = tmp1 + tmp6;
165	0	wsptr[DCTSIZE*6] = tmp1 - tmp6;
166	0	wsptr[DCTSIZE*2] = tmp2 + tmp5;
167	0	wsptr[DCTSIZE*5] = tmp2 - tmp5;
168	0	wsptr[DCTSIZE*4] = tmp3 + tmp4;
169	0	wsptr[DCTSIZE*3] = tmp3 - tmp4;
170
171	0	inptr++; /* advance pointers to next column */
172	0	quantptr++;
173	0	wsptr++;
174	0	}
175
176		/* Pass 2: process rows from work array, store into output array. */
177		/* Note that we must descale the results by a factor of 8 == 2*3. /
178
179	0	wsptr = workspace;
180	0	for (ctr = 0; ctr < DCTSIZE; ctr++) {
181	0	outptr = output_buf[ctr] + output_col;
182		/* Rows of zeroes can be exploited in the same way as we did with columns.
183		* However, the column calculation has created many nonzero AC terms, so
184		* the simplification applies less often (typically 5% to 10% of the time).
185		* And testing floats for zero is relatively expensive, so we don't bother.
186		*/
187
188		/* Even part */
189
190	0	tmp10 = wsptr[0] + wsptr[4];
191	0	tmp11 = wsptr[0] - wsptr[4];
192
193	0	tmp13 = wsptr[2] + wsptr[6];
194	0	tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;
195
196	0	tmp0 = tmp10 + tmp13;
197	0	tmp3 = tmp10 - tmp13;
198	0	tmp1 = tmp11 + tmp12;
199	0	tmp2 = tmp11 - tmp12;
200
201		/* Odd part */
202
203	0	z13 = wsptr[5] + wsptr[3];
204	0	z10 = wsptr[5] - wsptr[3];
205	0	z11 = wsptr[1] + wsptr[7];
206	0	z12 = wsptr[1] - wsptr[7];
207
208	0	tmp7 = z11 + z13;
209	0	tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);
210
211	0	z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2c2 /
212	0	tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2(c2-c6) /
213	0	tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2(c2+c6) /
214
215	0	tmp6 = tmp12 - tmp7;
216	0	tmp5 = tmp11 - tmp6;
217	0	tmp4 = tmp10 + tmp5;
218
219		/* Final output stage: scale down by a factor of 8 and range-limit */
220
221	0	outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
222	0	& RANGE_MASK];
223	0	outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
224	0	& RANGE_MASK];
225	0	outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
226	0	& RANGE_MASK];
227	0	outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
228	0	& RANGE_MASK];
229	0	outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
230	0	& RANGE_MASK];
231	0	outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
232	0	& RANGE_MASK];
233	0	outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
234	0	& RANGE_MASK];
235	0	outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
236	0	& RANGE_MASK];
237
238	0	wsptr += DCTSIZE; /* advance pointer to next row */
239	0	}
240	0	}
241
242		#endif /* DCT_FLOAT_SUPPORTED */