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 }