libmad/bit.c

   1 /*
   2  * libmad - MPEG audio decoder library
   3  * Copyright (C) 2000-2003 Underbit Technologies, Inc.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18  *
  19  */
  20
  21 # ifdef HAVE_CONFIG_H
  22 #  include "config.h"
  23 # endif
  24
  25 # include "global.h"
  26
  27 # ifdef HAVE_LIMITS_H
  28 #  include <limits.h>
  29 # else
  30 #  define CHAR_BIT  8
  31 # endif
  32
  33 # include "bit.h"
  34
  35 /*
  36  * This is the lookup table for computing the CRC-check word.
  37  * As described in section 2.4.3.1 and depicted in Figure A.9
  38  * of ISO/IEC 11172-3, the generator polynomial is:
  39  *
  40  * G(X) = X^16 + X^15 + X^2 + 1
  41  */
  42 static
  43 u16 const crc_table[256] = {
  44   0x0000, 0x8005, 0x800f, 0x000a, 0x801b, 0x001e, 0x0014, 0x8011,
  45   0x8033, 0x0036, 0x003c, 0x8039, 0x0028, 0x802d, 0x8027, 0x0022,
  46   0x8063, 0x0066, 0x006c, 0x8069, 0x0078, 0x807d, 0x8077, 0x0072,
  47   0x0050, 0x8055, 0x805f, 0x005a, 0x804b, 0x004e, 0x0044, 0x8041,
  48   0x80c3, 0x00c6, 0x00cc, 0x80c9, 0x00d8, 0x80dd, 0x80d7, 0x00d2,
  49   0x00f0, 0x80f5, 0x80ff, 0x00fa, 0x80eb, 0x00ee, 0x00e4, 0x80e1,
  50   0x00a0, 0x80a5, 0x80af, 0x00aa, 0x80bb, 0x00be, 0x00b4, 0x80b1,
  51   0x8093, 0x0096, 0x009c, 0x8099, 0x0088, 0x808d, 0x8087, 0x0082,
  52
  53   0x8183, 0x0186, 0x018c, 0x8189, 0x0198, 0x819d, 0x8197, 0x0192,
  54   0x01b0, 0x81b5, 0x81bf, 0x01ba, 0x81ab, 0x01ae, 0x01a4, 0x81a1,
  55   0x01e0, 0x81e5, 0x81ef, 0x01ea, 0x81fb, 0x01fe, 0x01f4, 0x81f1,
  56   0x81d3, 0x01d6, 0x01dc, 0x81d9, 0x01c8, 0x81cd, 0x81c7, 0x01c2,
  57   0x0140, 0x8145, 0x814f, 0x014a, 0x815b, 0x015e, 0x0154, 0x8151,
  58   0x8173, 0x0176, 0x017c, 0x8179, 0x0168, 0x816d, 0x8167, 0x0162,
  59   0x8123, 0x0126, 0x012c, 0x8129, 0x0138, 0x813d, 0x8137, 0x0132,
  60   0x0110, 0x8115, 0x811f, 0x011a, 0x810b, 0x010e, 0x0104, 0x8101,
  61
  62   0x8303, 0x0306, 0x030c, 0x8309, 0x0318, 0x831d, 0x8317, 0x0312,
  63   0x0330, 0x8335, 0x833f, 0x033a, 0x832b, 0x032e, 0x0324, 0x8321,
  64   0x0360, 0x8365, 0x836f, 0x036a, 0x837b, 0x037e, 0x0374, 0x8371,
  65   0x8353, 0x0356, 0x035c, 0x8359, 0x0348, 0x834d, 0x8347, 0x0342,
  66   0x03c0, 0x83c5, 0x83cf, 0x03ca, 0x83db, 0x03de, 0x03d4, 0x83d1,
  67   0x83f3, 0x03f6, 0x03fc, 0x83f9, 0x03e8, 0x83ed, 0x83e7, 0x03e2,
  68   0x83a3, 0x03a6, 0x03ac, 0x83a9, 0x03b8, 0x83bd, 0x83b7, 0x03b2,
  69   0x0390, 0x8395, 0x839f, 0x039a, 0x838b, 0x038e, 0x0384, 0x8381,
  70
  71   0x0280, 0x8285, 0x828f, 0x028a, 0x829b, 0x029e, 0x0294, 0x8291,
  72   0x82b3, 0x02b6, 0x02bc, 0x82b9, 0x02a8, 0x82ad, 0x82a7, 0x02a2,
  73   0x82e3, 0x02e6, 0x02ec, 0x82e9, 0x02f8, 0x82fd, 0x82f7, 0x02f2,
  74   0x02d0, 0x82d5, 0x82df, 0x02da, 0x82cb, 0x02ce, 0x02c4, 0x82c1,
  75   0x8243, 0x0246, 0x024c, 0x8249, 0x0258, 0x825d, 0x8257, 0x0252,
  76   0x0270, 0x8275, 0x827f, 0x027a, 0x826b, 0x026e, 0x0264, 0x8261,
  77   0x0220, 0x8225, 0x822f, 0x022a, 0x823b, 0x023e, 0x0234, 0x8231,
  78   0x8213, 0x0216, 0x021c, 0x8219, 0x0208, 0x820d, 0x8207, 0x0202
  79 };
  80
  81 # define CRC_POLY  0x8005
  82
  83 /*
  84  * NAME:        bit->init()
  85  * DESCRIPTION: initialize bit pointer struct
  86  */
  87 void mad_bit_init(struct mad_bitptr *bitptr, u8 const *byte)
  88 {
  89   bitptr->byte  = byte;
  90   bitptr->cache = 0;
  91   bitptr->left  = CHAR_BIT;
  92 }
  93
  94 /*
  95  * NAME:        bit->length()
  96  * DESCRIPTION: return number of bits between start and end points
  97  */
  98 u32 mad_bit_length(struct mad_bitptr const *begin,
  99                             struct mad_bitptr const *end)
 100 {
 101   return begin->left +
 102     CHAR_BIT * (end->byte - (begin->byte + 1)) + (CHAR_BIT - end->left);
 103 }
 104
 105 /*
 106  * NAME:        bit->nextbyte()
 107  * DESCRIPTION: return pointer to next unprocessed byte
 108  */
 109 u8 const *mad_bit_nextbyte(struct mad_bitptr const *bitptr)
 110 {
 111   return bitptr->left == CHAR_BIT ? bitptr->byte : bitptr->byte + 1;
 112 }
 113
 114 /*
 115  * NAME:        bit->skip()
 116  * DESCRIPTION: advance bit pointer
 117  */
 118 void mad_bit_skip(struct mad_bitptr *bitptr, u32 len)
 119 {
 120   bitptr->byte += len / CHAR_BIT;
 121   bitptr->left -= len % CHAR_BIT;
 122
 123   if (bitptr->left > CHAR_BIT) {
 124     bitptr->byte++;
 125     bitptr->left += CHAR_BIT;
 126   }
 127
 128   if (bitptr->left < CHAR_BIT)
 129     bitptr->cache = *bitptr->byte;
 130 }
 131
 132 /*
 133  * NAME:        bit->read()
 134  * DESCRIPTION: read an arbitrary number of bits and return their UIMSBF value
 135  */
 136 u32 mad_bit_read(struct mad_bitptr *bitptr, u32 len)
 137 {
 138   register u32 value;
 139
 140   if (bitptr->left == CHAR_BIT)
 141     bitptr->cache = *bitptr->byte;
 142
 143   if (len < bitptr->left) {
 144     value = (bitptr->cache & ((1 << bitptr->left) - 1)) >>
 145       (bitptr->left - len);
 146     bitptr->left -= len;
 147
 148     return value;
 149   }
 150
 151   /* remaining bits in current byte */
 152
 153   value = bitptr->cache & ((1 << bitptr->left) - 1);
 154   len  -= bitptr->left;
 155
 156   bitptr->byte++;
 157   bitptr->left = CHAR_BIT;
 158
 159   /* more bytes */
 160
 161   while (len >= CHAR_BIT) {
 162     value = (value << CHAR_BIT) | *bitptr->byte++;
 163     len  -= CHAR_BIT;
 164   }
 165
 166   if (len > 0) {
 167     bitptr->cache = *bitptr->byte;
 168
 169     value = (value << len) | (bitptr->cache >> (CHAR_BIT - len));
 170     bitptr->left -= len;
 171   }
 172
 173   return value;
 174 }
 175
 176 # if 0
 177 /*
 178  * NAME:        bit->write()
 179  * DESCRIPTION: write an arbitrary number of bits
 180  */
 181 void mad_bit_write(struct mad_bitptr *bitptr, u32 len,
 182                    u32 value)
 183 {
 184   u8 *ptr;
 185
 186   ptr = (u8 *) bitptr->byte;
 187
 188   /* ... */
 189 }
 190 # endif
 191
 192 /*
 193  * NAME:        bit->crc()
 194  * DESCRIPTION: compute CRC-check word
 195  */
 196 u16 mad_bit_crc(struct mad_bitptr bitptr, u32 len,
 197                            u16 init)
 198 {
 199   register u32 crc;
 200
 201   for (crc = init; len >= 32; len -= 32) {
 202     register u32 data;
 203
 204     data = mad_bit_read(&bitptr, 32);
 205
 206     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 24)) & 0xff];
 207     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 16)) & 0xff];
 208     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >>  8)) & 0xff];
 209     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >>  0)) & 0xff];
 210   }
 211
 212   switch (len / 8) {
 213   case 3: crc = (crc << 8) ^
 214             crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
 215   case 2: crc = (crc << 8) ^
 216             crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
 217   case 1: crc = (crc << 8) ^
 218             crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
 219
 220   len %= 8;
 221
 222   case 0: break;
 223   }
 224
 225   while (len--) {
 226     register u32 msb;
 227
 228     msb = mad_bit_read(&bitptr, 1) ^ (crc >> 15);
 229
 230     crc <<= 1;
 231     if (msb & 1)
 232       crc ^= CRC_POLY;
 233   }
 234
 235   return crc & 0xffff;
 236 }