rtoss - Blame information for rev 26

Subversion Repositories:
Rev:
Rev Author Line No. Line
14 roytam 1 /*
2  * libmad - MPEG audio decoder library
26 roytam 3  * Copyright (C) 2000-2004 Underbit Technologies, Inc.
14 roytam 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  *
26 roytam 19  * $Id: bit.c,v 1.12 2004/01/23 09:41:32 rob Exp $
14 roytam 20  */
21  
22 # ifdef HAVE_CONFIG_H
23 #  include "config.h"
24 # endif
25  
26 # include "global.h"
27  
28 # ifdef HAVE_LIMITS_H
29 #  include <limits.h>
30 # else
31 #  define CHAR_BIT  8
32 # endif
33  
34 # include "bit.h"
35  
36 /*
37  * This is the lookup table for computing the CRC-check word.
38  * As described in section 2.4.3.1 and depicted in Figure A.9
39  * of ISO/IEC 11172-3, the generator polynomial is:
40  *
41  * G(X) = X^16 + X^15 + X^2 + 1
42  */
43 static
44 unsigned short const crc_table[256] = {
45   0x0000, 0x8005, 0x800f, 0x000a, 0x801b, 0x001e, 0x0014, 0x8011,
46   0x8033, 0x0036, 0x003c, 0x8039, 0x0028, 0x802d, 0x8027, 0x0022,
47   0x8063, 0x0066, 0x006c, 0x8069, 0x0078, 0x807d, 0x8077, 0x0072,
48   0x0050, 0x8055, 0x805f, 0x005a, 0x804b, 0x004e, 0x0044, 0x8041,
49   0x80c3, 0x00c6, 0x00cc, 0x80c9, 0x00d8, 0x80dd, 0x80d7, 0x00d2,
50   0x00f0, 0x80f5, 0x80ff, 0x00fa, 0x80eb, 0x00ee, 0x00e4, 0x80e1,
51   0x00a0, 0x80a5, 0x80af, 0x00aa, 0x80bb, 0x00be, 0x00b4, 0x80b1,
52   0x8093, 0x0096, 0x009c, 0x8099, 0x0088, 0x808d, 0x8087, 0x0082,
53  
54   0x8183, 0x0186, 0x018c, 0x8189, 0x0198, 0x819d, 0x8197, 0x0192,
55   0x01b0, 0x81b5, 0x81bf, 0x01ba, 0x81ab, 0x01ae, 0x01a4, 0x81a1,
56   0x01e0, 0x81e5, 0x81ef, 0x01ea, 0x81fb, 0x01fe, 0x01f4, 0x81f1,
57   0x81d3, 0x01d6, 0x01dc, 0x81d9, 0x01c8, 0x81cd, 0x81c7, 0x01c2,
58   0x0140, 0x8145, 0x814f, 0x014a, 0x815b, 0x015e, 0x0154, 0x8151,
59   0x8173, 0x0176, 0x017c, 0x8179, 0x0168, 0x816d, 0x8167, 0x0162,
60   0x8123, 0x0126, 0x012c, 0x8129, 0x0138, 0x813d, 0x8137, 0x0132,
61   0x0110, 0x8115, 0x811f, 0x011a, 0x810b, 0x010e, 0x0104, 0x8101,
62  
63   0x8303, 0x0306, 0x030c, 0x8309, 0x0318, 0x831d, 0x8317, 0x0312,
64   0x0330, 0x8335, 0x833f, 0x033a, 0x832b, 0x032e, 0x0324, 0x8321,
65   0x0360, 0x8365, 0x836f, 0x036a, 0x837b, 0x037e, 0x0374, 0x8371,
66   0x8353, 0x0356, 0x035c, 0x8359, 0x0348, 0x834d, 0x8347, 0x0342,
67   0x03c0, 0x83c5, 0x83cf, 0x03ca, 0x83db, 0x03de, 0x03d4, 0x83d1,
68   0x83f3, 0x03f6, 0x03fc, 0x83f9, 0x03e8, 0x83ed, 0x83e7, 0x03e2,
69   0x83a3, 0x03a6, 0x03ac, 0x83a9, 0x03b8, 0x83bd, 0x83b7, 0x03b2,
70   0x0390, 0x8395, 0x839f, 0x039a, 0x838b, 0x038e, 0x0384, 0x8381,
71  
72   0x0280, 0x8285, 0x828f, 0x028a, 0x829b, 0x029e, 0x0294, 0x8291,
73   0x82b3, 0x02b6, 0x02bc, 0x82b9, 0x02a8, 0x82ad, 0x82a7, 0x02a2,
74   0x82e3, 0x02e6, 0x02ec, 0x82e9, 0x02f8, 0x82fd, 0x82f7, 0x02f2,
75   0x02d0, 0x82d5, 0x82df, 0x02da, 0x82cb, 0x02ce, 0x02c4, 0x82c1,
76   0x8243, 0x0246, 0x024c, 0x8249, 0x0258, 0x825d, 0x8257, 0x0252,
77   0x0270, 0x8275, 0x827f, 0x027a, 0x826b, 0x026e, 0x0264, 0x8261,
78   0x0220, 0x8225, 0x822f, 0x022a, 0x823b, 0x023e, 0x0234, 0x8231,
79   0x8213, 0x0216, 0x021c, 0x8219, 0x0208, 0x820d, 0x8207, 0x0202
80 };
81  
82 # define CRC_POLY  0x8005
83  
84 /*
85  * NAME:        bit->init()
86  * DESCRIPTION: initialize bit pointer struct
87  */
88 void mad_bit_init(struct mad_bitptr *bitptr, unsigned char const *byte)
89 {
90   bitptr->byte  = byte;
91   bitptr->cache = 0;
92   bitptr->left  = CHAR_BIT;
93 }
94  
95 /*
96  * NAME:        bit->length()
97  * DESCRIPTION: return number of bits between start and end points
98  */
99 unsigned int mad_bit_length(struct mad_bitptr const *begin,
100                             struct mad_bitptr const *end)
101 {
102   return begin->left +
103     CHAR_BIT * (end->byte - (begin->byte + 1)) + (CHAR_BIT - end->left);
104 }
105  
106 /*
107  * NAME:        bit->nextbyte()
108  * DESCRIPTION: return pointer to next unprocessed byte
109  */
110 unsigned char const *mad_bit_nextbyte(struct mad_bitptr const *bitptr)
111 {
112   return bitptr->left == CHAR_BIT ? bitptr->byte : bitptr->byte + 1;
113 }
114  
115 /*
116  * NAME:        bit->skip()
117  * DESCRIPTION: advance bit pointer
118  */
119 void mad_bit_skip(struct mad_bitptr *bitptr, unsigned int len)
120 {
121   bitptr->byte += len / CHAR_BIT;
122   bitptr->left -= len % CHAR_BIT;
123  
124   if (bitptr->left > CHAR_BIT) {
125     bitptr->byte++;
126     bitptr->left += CHAR_BIT;
127   }
128  
129   if (bitptr->left < CHAR_BIT)
130     bitptr->cache = *bitptr->byte;
131 }
132  
133 /*
134  * NAME:        bit->read()
135  * DESCRIPTION: read an arbitrary number of bits and return their UIMSBF value
136  */
137 unsigned long mad_bit_read(struct mad_bitptr *bitptr, unsigned int len)
138 {
139   register unsigned long value;
140  
141   if (bitptr->left == CHAR_BIT)
142     bitptr->cache = *bitptr->byte;
143  
144   if (len < bitptr->left) {
145     value = (bitptr->cache & ((1 << bitptr->left) - 1)) >>
146       (bitptr->left - len);
147     bitptr->left -= len;
148  
149     return value;
150   }
151  
152   /* remaining bits in current byte */
153  
154   value = bitptr->cache & ((1 << bitptr->left) - 1);
155   len  -= bitptr->left;
156  
157   bitptr->byte++;
158   bitptr->left = CHAR_BIT;
159  
160   /* more bytes */
161  
162   while (len >= CHAR_BIT) {
163     value = (value << CHAR_BIT) | *bitptr->byte++;
164     len  -= CHAR_BIT;
165   }
166  
167   if (len > 0) {
168     bitptr->cache = *bitptr->byte;
169  
170     value = (value << len) | (bitptr->cache >> (CHAR_BIT - len));
171     bitptr->left -= len;
172   }
173  
174   return value;
175 }
176  
177 # if 0
178 /*
179  * NAME:        bit->write()
180  * DESCRIPTION: write an arbitrary number of bits
181  */
182 void mad_bit_write(struct mad_bitptr *bitptr, unsigned int len,
183                    unsigned long value)
184 {
185   unsigned char *ptr;
186  
187   ptr = (unsigned char *) bitptr->byte;
188  
189   /* ... */
190 }
191 # endif
192  
193 /*
194  * NAME:        bit->crc()
195  * DESCRIPTION: compute CRC-check word
196  */
197 unsigned short mad_bit_crc(struct mad_bitptr bitptr, unsigned int len,
198                            unsigned short init)
199 {
200   register unsigned int crc;
201  
202   for (crc = init; len >= 32; len -= 32) {
203     register unsigned long data;
204  
205     data = mad_bit_read(&bitptr, 32);
206  
207     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 24)) & 0xff];
208     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 16)) & 0xff];
209     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >>  8)) & 0xff];
210     crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >>  0)) & 0xff];
211   }
212  
213   switch (len / 8) {
214   case 3: crc = (crc << 8) ^
215             crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
216   case 2: crc = (crc << 8) ^
217             crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
218   case 1: crc = (crc << 8) ^
219             crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff];
220  
221   len %= 8;
222  
223   case 0: break;
224   }
225  
226   while (len--) {
227     register unsigned int msb;
228  
229     msb = mad_bit_read(&bitptr, 1) ^ (crc >> 15);
230  
231     crc <<= 1;
232     if (msb & 1)
233       crc ^= CRC_POLY;
234   }
235  
236   return crc & 0xffff;
237 }