libdvdread4/bitreader.c

   1 /*
   2  * Copyright (C) 2000, 2001, 2002, 2003 Håkan Hjort <d95hjort@dtek.chalmers.se>
   3  *
   4  * This file is part of libdvdread.
   5  *
   6  * libdvdread is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * libdvdread is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License along
  17  * with libdvdread; if not, write to the Free Software Foundation, Inc.,
  18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  19  */
  20
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <inttypes.h>
  25
  26 #include "dvdread/bitreader.h"
  27
  28 int dvdread_getbits_init(getbits_state_t *state, uint8_t *start) {
  29   if ((state == NULL) || (start == NULL)) return 0;
  30   state->start = start;
  31   state->bit_position = 0;
  32   state->byte_position = 0;
  33   state->byte = start[0];
  34   return 1;
  35 }
  36
  37 /* Non-optimized getbits. */
  38 /* This can easily be optimized for particular platforms. */
  39 uint32_t dvdread_getbits(getbits_state_t *state, uint32_t number_of_bits) {
  40   uint32_t result=0;
  41   uint8_t byte=0;
  42   if (number_of_bits > 32) {
  43     printf("Number of bits > 32 in getbits\n");
  44     abort();
  45   }
  46
  47   if ((state->bit_position) > 0) {  /* Last getbits left us in the middle of a byte. */
  48     if (number_of_bits > (8-state->bit_position)) { /* this getbits will span 2 or more bytes. */
  49       byte = state->byte;
  50       byte = byte >> (state->bit_position);
  51       result = byte;
  52       number_of_bits -= (8-state->bit_position);
  53       state->bit_position = 0;
  54       state->byte_position++;
  55       state->byte = state->start[state->byte_position];
  56     } else {
  57       byte=state->byte;
  58       state->byte = state->byte << number_of_bits;
  59       byte = byte >> (8 - number_of_bits);
  60       result = byte;
  61       state->bit_position += number_of_bits; /* Here it is impossible for bit_position > 8 */
  62       if (state->bit_position == 8) {
  63         state->bit_position = 0;
  64         state->byte_position++;
  65         state->byte = state->start[state->byte_position];
  66       }
  67       number_of_bits = 0;
  68     }
  69   }
  70   if ((state->bit_position) == 0) {
  71     while (number_of_bits > 7) {
  72       result = (result << 8) + state->byte;
  73       state->byte_position++;
  74       state->byte = state->start[state->byte_position];
  75       number_of_bits -= 8;
  76     }
  77     if (number_of_bits > 0) { /* number_of_bits < 8 */
  78       byte = state->byte;
  79       state->byte = state->byte << number_of_bits;
  80       state->bit_position += number_of_bits; /* Here it is impossible for bit_position > 7 */
  81       byte = byte >> (8 - number_of_bits);
  82       result = (result << number_of_bits) + byte;
  83       number_of_bits = 0;
  84     }
  85   }
  86
  87   return result;
  88 }
  89
  90 #if 0  /* TODO: optimized versions not yet used */
  91
  92 /* WARNING: This function can only be used on a byte boundary.
  93             No checks are made that we are in fact on a byte boundary.
  94  */
  95 uint16_t dvdread_get16bits(getbits_state_t *state) {
  96   uint16_t result;
  97   state->byte_position++;
  98   result = (state->byte << 8) + state->start[state->byte_position++];
  99   state->byte = state->start[state->byte_position];
 100   return result;
 101 }
 102
 103 /* WARNING: This function can only be used on a byte boundary.
 104             No checks are made that we are in fact on a byte boundary.
 105  */
 106 uint32_t dvdread_get32bits(getbits_state_t *state) {
 107   uint32_t result;
 108   state->byte_position++;
 109   result = (state->byte << 8) + state->start[state->byte_position++];
 110   result = (result << 8) + state->start[state->byte_position++];
 111   result = (result << 8) + state->start[state->byte_position++];
 112   state->byte = state->start[state->byte_position];
 113   return result;
 114 }
 115
 116 #endif