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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 GLOBAL(long)
     90 jmin (long a, long b)
     91 {
     92   return a < b ? a : b;
     93 }
     94 
     95 
     96 /* On normal machines we can apply MEMCOPY() and MEMZERO() to sample arrays
     97  * and coefficient-block arrays.  This won't work on 80x86 because the arrays
     98  * are FAR and we're assuming a small-pointer memory model.  However, some
     99  * DOS compilers provide far-pointer versions of memcpy() and memset() even
    100  * in the small-model libraries.  These will be used if USE_FMEM is defined.
    101  * Otherwise, the routines below do it the hard way.  (The performance cost
    102  * is not all that great, because these routines aren't very heavily used.)
    103  */
    104 
    105 #ifndef NEED_FAR_POINTERS	/* normal case, same as regular macros */
    106 #define FMEMCOPY(dest,src,size)	MEMCOPY(dest,src,size)
    107 #define FMEMZERO(target,size)	MEMZERO(target,size)
    108 #else				/* 80x86 case, define if we can */
    109 #ifdef USE_FMEM
    110 #define FMEMCOPY(dest,src,size)	_fmemcpy((void FAR *)(dest), (const void FAR *)(src), (size_t)(size))
    111 #define FMEMZERO(target,size)	_fmemset((void FAR *)(target), 0, (size_t)(size))
    112 #endif
    113 #endif
    114 
    115 
    116 GLOBAL(void)
    117 jcopy_sample_rows (JSAMPARRAY input_array, int source_row,
    118 		   JSAMPARRAY output_array, int dest_row,
    119 		   int num_rows, JDIMENSION num_cols)
    120 /* Copy some rows of samples from one place to another.
    121  * num_rows rows are copied from input_array[source_row++]
    122  * to output_array[dest_row++]; these areas may overlap for duplication.
    123  * The source and destination arrays must be at least as wide as num_cols.
    124  */
    125 {
    126   register JSAMPROW inptr, outptr;
    127 #ifdef FMEMCOPY
    128   register size_t count = (size_t) (num_cols * SIZEOF(JSAMPLE));
    129 #else
    130   register JDIMENSION count;
    131 #endif
    132   register int row;
    133 
    134   input_array += source_row;
    135   output_array += dest_row;
    136 
    137   for (row = num_rows; row > 0; row--) {
    138     inptr = *input_array++;
    139     outptr = *output_array++;
    140 #ifdef FMEMCOPY
    141     FMEMCOPY(outptr, inptr, count);
    142 #else
    143     for (count = num_cols; count > 0; count--)
    144       *outptr++ = *inptr++;	/* needn't bother with GETJSAMPLE() here */
    145 #endif
    146   }
    147 }
    148 
    149 
    150 GLOBAL(void)
    151 jcopy_block_row (JBLOCKROW input_row, JBLOCKROW output_row,
    152 		 JDIMENSION num_blocks)
    153 /* Copy a row of coefficient blocks from one place to another. */
    154 {
    155 #ifdef FMEMCOPY
    156   FMEMCOPY(output_row, input_row, num_blocks * (DCTSIZE2 * SIZEOF(JCOEF)));
    157 #else
    158   register JCOEFPTR inptr, outptr;
    159   register long count;
    160 
    161   inptr = (JCOEFPTR) input_row;
    162   outptr = (JCOEFPTR) output_row;
    163   for (count = (long) num_blocks * DCTSIZE2; count > 0; count--) {
    164     *outptr++ = *inptr++;
    165   }
    166 #endif
    167 }
    168 
    169 
    170 GLOBAL(void)
    171 jzero_far (void FAR * target, size_t bytestozero)
    172 /* Zero out a chunk of FAR memory. */
    173 /* This might be sample-array data, block-array data, or alloc_large data. */
    174 {
    175 #ifdef FMEMZERO
    176   FMEMZERO(target, bytestozero);
    177 #else
    178   register char FAR * ptr = (char FAR *) target;
    179   register size_t count;
    180 
    181   for (count = bytestozero; count > 0; count--) {
    182     *ptr++ = 0;
    183   }
    184 #endif
    185 }
    186