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jutils.c (5240B)
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1 /*
2 * jutils.c
3 *
4 * Copyright (C) 1991-1996, 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 tables and miscellaneous utility routines needed
9 * for both compression and decompression.
10 * Note we prefix all global names with "j" to minimize conflicts with
11 * a surrounding application.
12 */
13
14 #define JPEG_INTERNALS
15 #include "jinclude.h"
16 #include "jpeglib.h"
17
18
19 /*
20 * jpeg_zigzag_order[i] is the zigzag-order position of the i'th element
21 * of a DCT block read in natural order (left to right, top to bottom).
22 */
23
24 #if 0 /* This table is not actually needed in v6a */
25
26 const int jpeg_zigzag_order[DCTSIZE2] = {
27 0, 1, 5, 6, 14, 15, 27, 28,
28 2, 4, 7, 13, 16, 26, 29, 42,
29 3, 8, 12, 17, 25, 30, 41, 43,
30 9, 11, 18, 24, 31, 40, 44, 53,
31 10, 19, 23, 32, 39, 45, 52, 54,
32 20, 22, 33, 38, 46, 51, 55, 60,
33 21, 34, 37, 47, 50, 56, 59, 61,
34 35, 36, 48, 49, 57, 58, 62, 63
35 };
36
37 #endif
38
39 /*
40 * jpeg_natural_order[i] is the natural-order position of the i'th element
41 * of zigzag order.
42 *
43 * When reading corrupted data, the Huffman decoders could attempt
44 * to reference an entry beyond the end of this array (if the decoded
45 * zero run length reaches past the end of the block). To prevent
46 * wild stores without adding an inner-loop test, we put some extra
47 * "63"s after the real entries. This will cause the extra coefficient
48 * to be stored in location 63 of the block, not somewhere random.
49 * The worst case would be a run-length of 15, which means we need 16
50 * fake entries.
51 */
52
53 const int jpeg_natural_order[DCTSIZE2+16] = {
54 0, 1, 8, 16, 9, 2, 3, 10,
55 17, 24, 32, 25, 18, 11, 4, 5,
56 12, 19, 26, 33, 40, 48, 41, 34,
57 27, 20, 13, 6, 7, 14, 21, 28,
58 35, 42, 49, 56, 57, 50, 43, 36,
59 29, 22, 15, 23, 30, 37, 44, 51,
60 58, 59, 52, 45, 38, 31, 39, 46,
61 53, 60, 61, 54, 47, 55, 62, 63,
62 63, 63, 63, 63, 63, 63, 63, 63, /* extra entries for safety in decoder */
63 63, 63, 63, 63, 63, 63, 63, 63
64 };
65
66
67 /*
68 * Arithmetic utilities
69 */
70
71 GLOBAL(long)
72 jdiv_round_up (long a, long b)
73 /* Compute a/b rounded up to next integer, ie, ceil(a/b) */
74 /* Assumes a >= 0, b > 0 */
75 {
76 return (a + b - 1L) / b;
77 }
78
79
80 GLOBAL(long)
81 jround_up (long a, long b)
82 /* Compute a rounded up to next multiple of b, ie, ceil(a/b)*b */
83 /* Assumes a >= 0, b > 0 */
84 {
85 a += b - 1L;
86 return a - (a % b);
87 }
88
89
90 /* On normal machines we can apply MEMCOPY() and MEMZERO() to sample arrays
91 * and coefficient-block arrays. This won't work on 80x86 because the arrays
92 * are FAR and we're assuming a small-pointer memory model. However, some
93 * DOS compilers provide far-pointer versions of memcpy() and memset() even
94 * in the small-model libraries. These will be used if USE_FMEM is defined.
95 * Otherwise, the routines below do it the hard way. (The performance cost
96 * is not all that great, because these routines aren't very heavily used.)
97 */
98
99 #ifndef NEED_FAR_POINTERS /* normal case, same as regular macros */
100 #define FMEMCOPY(dest,src,size) MEMCOPY(dest,src,size)
101 #define FMEMZERO(target,size) MEMZERO(target,size)
102 #else /* 80x86 case, define if we can */
103 #ifdef USE_FMEM
104 #define FMEMCOPY(dest,src,size) _fmemcpy((void FAR *)(dest), (const void FAR *)(src), (size_t)(size))
105 #define FMEMZERO(target,size) _fmemset((void FAR *)(target), 0, (size_t)(size))
106 #endif
107 #endif
108
109
110 GLOBAL(void)
111 jcopy_sample_rows (JSAMPARRAY input_array, int source_row,
112 JSAMPARRAY output_array, int dest_row,
113 int num_rows, JDIMENSION num_cols)
114 /* Copy some rows of samples from one place to another.
115 * num_rows rows are copied from input_array[source_row++]
116 * to output_array[dest_row++]; these areas may overlap for duplication.
117 * The source and destination arrays must be at least as wide as num_cols.
118 */
119 {
120 register JSAMPROW inptr, outptr;
121 #ifdef FMEMCOPY
122 register size_t count = (size_t) (num_cols * SIZEOF(JSAMPLE));
123 #else
124 register JDIMENSION count;
125 #endif
126 register int row;
127
128 input_array += source_row;
129 output_array += dest_row;
130
131 for (row = num_rows; row > 0; row--) {
132 inptr = *input_array++;
133 outptr = *output_array++;
134 #ifdef FMEMCOPY
135 FMEMCOPY(outptr, inptr, count);
136 #else
137 for (count = num_cols; count > 0; count--)
138 *outptr++ = *inptr++; /* needn't bother with GETJSAMPLE() here */
139 #endif
140 }
141 }
142
143
144 GLOBAL(void)
145 jcopy_block_row (JBLOCKROW input_row, JBLOCKROW output_row,
146 JDIMENSION num_blocks)
147 /* Copy a row of coefficient blocks from one place to another. */
148 {
149 #ifdef FMEMCOPY
150 FMEMCOPY(output_row, input_row, num_blocks * (DCTSIZE2 * SIZEOF(JCOEF)));
151 #else
152 register JCOEFPTR inptr, outptr;
153 register long count;
154
155 inptr = (JCOEFPTR) input_row;
156 outptr = (JCOEFPTR) output_row;
157 for (count = (long) num_blocks * DCTSIZE2; count > 0; count--) {
158 *outptr++ = *inptr++;
159 }
160 #endif
161 }
162
163
164 GLOBAL(void)
165 jzero_far (void FAR * target, size_t bytestozero)
166 /* Zero out a chunk of FAR memory. */
167 /* This might be sample-array data, block-array data, or alloc_large data. */
168 {
169 #ifdef FMEMZERO
170 FMEMZERO(target, bytestozero);
171 #else
172 register char FAR * ptr = (char FAR *) target;
173 register size_t count;
174
175 for (count = bytestozero; count > 0; count--) {
176 *ptr++ = 0;
177 }
178 #endif
179 }