blob: b5550ecbf7378455756253648a99331dedfb50f6
1 | /* |
2 | * libmad - MPEG audio decoder library |
3 | * Copyright (C) 2000-2004 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 | * $Id: bit.c,v 1.12 2004/01/23 09:41:32 rob Exp $ |
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 | /* |
135 | * NAME: bit->read() |
136 | * DESCRIPTION: read an arbitrary number of bits and return their UIMSBF value |
137 | */ |
138 | unsigned long mad_bit_read(struct mad_bitptr *bitptr, unsigned int len) |
139 | { |
140 | register unsigned long value; |
141 | |
142 | if (bitptr->left == CHAR_BIT) { |
143 | bitptr->cache = *bitptr->byte; |
144 | } |
145 | |
146 | if (len < bitptr->left) { |
147 | value = (bitptr->cache & ((1 << bitptr->left) - 1)) >> |
148 | (bitptr->left - len); |
149 | bitptr->left -= len; |
150 | |
151 | return value; |
152 | } |
153 | |
154 | /* remaining bits in current byte */ |
155 | |
156 | value = bitptr->cache & ((1 << bitptr->left) - 1); |
157 | len -= bitptr->left; |
158 | |
159 | bitptr->byte++; |
160 | bitptr->left = CHAR_BIT; |
161 | |
162 | /* more bytes */ |
163 | |
164 | while (len >= CHAR_BIT) { |
165 | value = (value << CHAR_BIT) | *bitptr->byte++; |
166 | len -= CHAR_BIT; |
167 | } |
168 | |
169 | if (len > 0) { |
170 | bitptr->cache = *bitptr->byte; |
171 | |
172 | value = (value << len) | (bitptr->cache >> (CHAR_BIT - len)); |
173 | bitptr->left -= len; |
174 | } |
175 | |
176 | return value; |
177 | } |
178 | |
179 | # if 0 |
180 | /* |
181 | * NAME: bit->write() |
182 | * DESCRIPTION: write an arbitrary number of bits |
183 | */ |
184 | void mad_bit_write(struct mad_bitptr *bitptr, unsigned int len, |
185 | unsigned long value) |
186 | { |
187 | unsigned char *ptr; |
188 | |
189 | ptr = (unsigned char *) bitptr->byte; |
190 | |
191 | /* ... */ |
192 | } |
193 | # endif |
194 | |
195 | /* |
196 | * NAME: bit->crc() |
197 | * DESCRIPTION: compute CRC-check word |
198 | */ |
199 | unsigned short mad_bit_crc(struct mad_bitptr bitptr, unsigned int len, |
200 | unsigned short init) |
201 | { |
202 | register unsigned int crc; |
203 | |
204 | for (crc = init; len >= 32; len -= 32) { |
205 | register unsigned long data; |
206 | |
207 | data = mad_bit_read(&bitptr, 32); |
208 | |
209 | crc = (crc << 8) ^ crc_table[((crc >> 8) ^(data >> 24)) & 0xff]; |
210 | crc = (crc << 8) ^ crc_table[((crc >> 8) ^(data >> 16)) & 0xff]; |
211 | crc = (crc << 8) ^ crc_table[((crc >> 8) ^(data >> 8)) & 0xff]; |
212 | crc = (crc << 8) ^ crc_table[((crc >> 8) ^(data >> 0)) & 0xff]; |
213 | } |
214 | |
215 | switch (len / 8) { |
216 | case 3: |
217 | crc = (crc << 8) ^ |
218 | crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff]; |
219 | case 2: |
220 | crc = (crc << 8) ^ |
221 | crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff]; |
222 | case 1: |
223 | crc = (crc << 8) ^ |
224 | crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff]; |
225 | |
226 | len %= 8; |
227 | |
228 | case 0: |
229 | break; |
230 | } |
231 | |
232 | while (len--) { |
233 | register unsigned int msb; |
234 | |
235 | msb = mad_bit_read(&bitptr, 1) ^(crc >> 15); |
236 | |
237 | crc <<= 1; |
238 | if (msb & 1) { |
239 | crc ^= CRC_POLY; |
240 | } |
241 | } |
242 | |
243 | return crc & 0xffff; |
244 | } |
245 |