deps/libretro-common/formats/libchdr/libchdr_bitstream.c

   1 /* license:BSD-3-Clause
   2  * copyright-holders:Aaron Giles
   3 ***************************************************************************
   4
   5     bitstream.c
   6
   7     Helper classes for reading/writing at the bit level.
   8
   9 ***************************************************************************/
  10
  11 #include <stdlib.h>
  12 #include <libchdr/bitstream.h>
  13
  14 /***************************************************************************
  15  *  INLINE FUNCTIONS
  16  ***************************************************************************
  17  */
  18
  19 int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); }
  20
  21 /*-------------------------------------------------
  22  *  create_bitstream - constructor
  23  *-------------------------------------------------
  24  */
  25
  26 struct bitstream* create_bitstream(const void *src, uint32_t srclength)
  27 {
  28         struct bitstream* bitstream = (struct bitstream*)malloc(sizeof(struct bitstream));
  29         bitstream->buffer = 0;
  30         bitstream->bits = 0;
  31         bitstream->read = (const uint8_t*)src;
  32         bitstream->doffset = 0;
  33         bitstream->dlength = srclength;
  34         return bitstream;
  35 }
  36
  37 /*-----------------------------------------------------
  38  *  bitstream_peek - fetch the requested number of bits
  39  *  but don't advance the input pointer
  40  *-----------------------------------------------------
  41  */
  42
  43 uint32_t bitstream_peek(struct bitstream* bitstream, int numbits)
  44 {
  45         if (numbits == 0)
  46                 return 0;
  47
  48         /* fetch data if we need more */
  49         if (numbits > bitstream->bits)
  50         {
  51                 while (bitstream->bits <= 24)
  52                 {
  53                         if (bitstream->doffset < bitstream->dlength)
  54                                 bitstream->buffer |= bitstream->read[bitstream->doffset] << (24 - bitstream->bits);
  55                         bitstream->doffset++;
  56                         bitstream->bits += 8;
  57                 }
  58         }
  59
  60         /* return the data */
  61         return bitstream->buffer >> (32 - numbits);
  62 }
  63
  64 /*-----------------------------------------------------
  65  *  bitstream_remove - advance the input pointer by the
  66  *  specified number of bits
  67  *-----------------------------------------------------
  68  */
  69
  70 void bitstream_remove(struct bitstream* bitstream, int numbits)
  71 {
  72         bitstream->buffer <<= numbits;
  73         bitstream->bits -= numbits;
  74 }
  75
  76 /*-----------------------------------------------------
  77  *  bitstream_read - fetch the requested number of bits
  78  *-----------------------------------------------------
  79  */
  80
  81 uint32_t bitstream_read(struct bitstream* bitstream, int numbits)
  82 {
  83         uint32_t result = bitstream_peek(bitstream, numbits);
  84         bitstream_remove(bitstream, numbits);
  85         return result;
  86 }
  87
  88 /*-------------------------------------------------
  89  *  read_offset - return the current read offset
  90  *-------------------------------------------------
  91  */
  92
  93 uint32_t bitstream_read_offset(struct bitstream* bitstream)
  94 {
  95         uint32_t result = bitstream->doffset;
  96         int bits = bitstream->bits;
  97         while (bits >= 8)
  98         {
  99                 result--;
 100                 bits -= 8;
 101         }
 102         return result;
 103 }
 104
 105 /*-------------------------------------------------
 106  *  flush - flush to the nearest byte
 107  *-------------------------------------------------
 108  */
 109
 110 uint32_t bitstream_flush(struct bitstream* bitstream)
 111 {
 112         while (bitstream->bits >= 8)
 113         {
 114                 bitstream->doffset--;
 115                 bitstream->bits -= 8;
 116         }
 117         bitstream->bits = bitstream->buffer = 0;
 118         return bitstream->doffset;
 119 }