jutils.cpp (5170B)
1 /* 2 * jutils.c 3 * 4 * Copyright (C) 1991-1995, 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 const int jpeg_zigzag_order[DCTSIZE2] = { 25 0, 1, 5, 6, 14, 15, 27, 28, 26 2, 4, 7, 13, 16, 26, 29, 42, 27 3, 8, 12, 17, 25, 30, 41, 43, 28 9, 11, 18, 24, 31, 40, 44, 53, 29 10, 19, 23, 32, 39, 45, 52, 54, 30 20, 22, 33, 38, 46, 51, 55, 60, 31 21, 34, 37, 47, 50, 56, 59, 61, 32 35, 36, 48, 49, 57, 58, 62, 63 33 }; 34 35 /* 36 * jpeg_natural_order[i] is the natural-order position of the i'th element 37 * of zigzag order. 38 * 39 * When reading corrupted data, the Huffman decoders could attempt 40 * to reference an entry beyond the end of this array (if the decoded 41 * zero run length reaches past the end of the block). To prevent 42 * wild stores without adding an inner-loop test, we put some extra 43 * "63"s after the real entries. This will cause the extra coefficient 44 * to be stored in location 63 of the block, not somewhere random. 45 * The worst case would be a run-length of 15, which means we need 16 46 * fake entries. 47 */ 48 49 const int jpeg_natural_order[DCTSIZE2+16] = { 50 0, 1, 8, 16, 9, 2, 3, 10, 51 17, 24, 32, 25, 18, 11, 4, 5, 52 12, 19, 26, 33, 40, 48, 41, 34, 53 27, 20, 13, 6, 7, 14, 21, 28, 54 35, 42, 49, 56, 57, 50, 43, 36, 55 29, 22, 15, 23, 30, 37, 44, 51, 56 58, 59, 52, 45, 38, 31, 39, 46, 57 53, 60, 61, 54, 47, 55, 62, 63, 58 63, 63, 63, 63, 63, 63, 63, 63, /* extra entries for safety in decoder */ 59 63, 63, 63, 63, 63, 63, 63, 63 60 }; 61 62 63 /* 64 * Arithmetic utilities 65 */ 66 67 GLOBAL long 68 jdiv_round_up (long a, long b) 69 /* Compute a/b rounded up to next integer, ie, ceil(a/b) */ 70 /* Assumes a >= 0, b > 0 */ 71 { 72 return (a + b - 1L) / b; 73 } 74 75 76 GLOBAL long 77 jround_up (long a, long b) 78 /* Compute a rounded up to next multiple of b, ie, ceil(a/b)*b */ 79 /* Assumes a >= 0, b > 0 */ 80 { 81 a += b - 1L; 82 return a - (a % b); 83 } 84 85 86 /* On normal machines we can apply MEMCOPY() and MEMZERO() to sample arrays 87 * and coefficient-block arrays. This won't work on 80x86 because the arrays 88 * are FAR and we're assuming a small-pointer memory model. However, some 89 * DOS compilers provide far-pointer versions of memcpy() and memset() even 90 * in the small-model libraries. These will be used if USE_FMEM is defined. 91 * Otherwise, the routines below do it the hard way. (The performance cost 92 * is not all that great, because these routines aren't very heavily used.) 93 */ 94 95 #ifndef NEED_FAR_POINTERS /* normal case, same as regular macros */ 96 #define FMEMCOPY(dest,src,size) MEMCOPY(dest,src,size) 97 #define FMEMZERO(target,size) MEMZERO(target,size) 98 #else /* 80x86 case, define if we can */ 99 #ifdef USE_FMEM 100 #define FMEMCOPY(dest,src,size) _fmemcpy((void FAR *)(dest), (const void FAR *)(src), (size_t)(size)) 101 #define FMEMZERO(target,size) _fmemset((void FAR *)(target), 0, (size_t)(size)) 102 #endif 103 #endif 104 105 106 GLOBAL void 107 jcopy_sample_rows (JSAMPARRAY input_array, int source_row, 108 JSAMPARRAY output_array, int dest_row, 109 int num_rows, JDIMENSION num_cols) 110 /* Copy some rows of samples from one place to another. 111 * num_rows rows are copied from input_array[source_row++] 112 * to output_array[dest_row++]; these areas may overlap for duplication. 113 * The source and destination arrays must be at least as wide as num_cols. 114 */ 115 { 116 register JSAMPROW inptr, outptr; 117 #ifdef FMEMCOPY 118 register size_t count = (size_t) (num_cols * SIZEOF(JSAMPLE)); 119 #else 120 register JDIMENSION count; 121 #endif 122 register int row; 123 124 input_array += source_row; 125 output_array += dest_row; 126 127 for (row = num_rows; row > 0; row--) { 128 inptr = *input_array++; 129 outptr = *output_array++; 130 #ifdef FMEMCOPY 131 FMEMCOPY(outptr, inptr, count); 132 #else 133 for (count = num_cols; count > 0; count--) 134 *outptr++ = *inptr++; /* needn't bother with GETJSAMPLE() here */ 135 #endif 136 } 137 } 138 139 140 GLOBAL void 141 jcopy_block_row (JBLOCKROW input_row, JBLOCKROW output_row, 142 JDIMENSION num_blocks) 143 /* Copy a row of coefficient blocks from one place to another. */ 144 { 145 #ifdef FMEMCOPY 146 FMEMCOPY(output_row, input_row, num_blocks * (DCTSIZE2 * SIZEOF(JCOEF))); 147 #else 148 register JCOEFPTR inptr, outptr; 149 register long count; 150 151 inptr = (JCOEFPTR) input_row; 152 outptr = (JCOEFPTR) output_row; 153 for (count = (long) num_blocks * DCTSIZE2; count > 0; count--) { 154 *outptr++ = *inptr++; 155 } 156 #endif 157 } 158 159 160 GLOBAL void 161 jzero_far (void FAR * target, size_t bytestozero) 162 /* Zero out a chunk of FAR memory. */ 163 /* This might be sample-array data, block-array data, or alloc_large data. */ 164 { 165 #ifdef FMEMZERO 166 FMEMZERO(target, bytestozero); 167 #else 168 register char FAR * ptr = (char FAR *) target; 169 register size_t count; 170 171 for (count = bytestozero; count > 0; count--) { 172 *ptr++ = 0; 173 } 174 #endif 175 }