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Diffstat (limited to '')
| -rw-r--r-- | src/libmad/bit.c | 237 |
1 files changed, 237 insertions, 0 deletions
diff --git a/src/libmad/bit.c b/src/libmad/bit.c new file mode 100644 index 000000000..597422a22 --- /dev/null +++ b/src/libmad/bit.c @@ -0,0 +1,237 @@ +/* + * libmad - MPEG audio decoder library + * Copyright (C) 2000-2003 Underbit Technologies, Inc. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + * + * $Id: bit.c,v 1.1 2003/08/14 03:57:13 shank Exp $ + */ + +# ifdef HAVE_CONFIG_H +# include "config.h" +# endif + +# include "global.h" + +# ifdef HAVE_LIMITS_H +# include <limits.h> +# else +# define CHAR_BIT 8 +# endif + +# include "bit.h" + +/* + * This is the lookup table for computing the CRC-check word. + * As described in section 2.4.3.1 and depicted in Figure A.9 + * of ISO/IEC 11172-3, the generator polynomial is: + * + * G(X) = X^16 + X^15 + X^2 + 1 + */ +static +unsigned short const crc_table[256] = { + 0x0000, 0x8005, 0x800f, 0x000a, 0x801b, 0x001e, 0x0014, 0x8011, + 0x8033, 0x0036, 0x003c, 0x8039, 0x0028, 0x802d, 0x8027, 0x0022, + 0x8063, 0x0066, 0x006c, 0x8069, 0x0078, 0x807d, 0x8077, 0x0072, + 0x0050, 0x8055, 0x805f, 0x005a, 0x804b, 0x004e, 0x0044, 0x8041, + 0x80c3, 0x00c6, 0x00cc, 0x80c9, 0x00d8, 0x80dd, 0x80d7, 0x00d2, + 0x00f0, 0x80f5, 0x80ff, 0x00fa, 0x80eb, 0x00ee, 0x00e4, 0x80e1, + 0x00a0, 0x80a5, 0x80af, 0x00aa, 0x80bb, 0x00be, 0x00b4, 0x80b1, + 0x8093, 0x0096, 0x009c, 0x8099, 0x0088, 0x808d, 0x8087, 0x0082, + + 0x8183, 0x0186, 0x018c, 0x8189, 0x0198, 0x819d, 0x8197, 0x0192, + 0x01b0, 0x81b5, 0x81bf, 0x01ba, 0x81ab, 0x01ae, 0x01a4, 0x81a1, + 0x01e0, 0x81e5, 0x81ef, 0x01ea, 0x81fb, 0x01fe, 0x01f4, 0x81f1, + 0x81d3, 0x01d6, 0x01dc, 0x81d9, 0x01c8, 0x81cd, 0x81c7, 0x01c2, + 0x0140, 0x8145, 0x814f, 0x014a, 0x815b, 0x015e, 0x0154, 0x8151, + 0x8173, 0x0176, 0x017c, 0x8179, 0x0168, 0x816d, 0x8167, 0x0162, + 0x8123, 0x0126, 0x012c, 0x8129, 0x0138, 0x813d, 0x8137, 0x0132, + 0x0110, 0x8115, 0x811f, 0x011a, 0x810b, 0x010e, 0x0104, 0x8101, + + 0x8303, 0x0306, 0x030c, 0x8309, 0x0318, 0x831d, 0x8317, 0x0312, + 0x0330, 0x8335, 0x833f, 0x033a, 0x832b, 0x032e, 0x0324, 0x8321, + 0x0360, 0x8365, 0x836f, 0x036a, 0x837b, 0x037e, 0x0374, 0x8371, + 0x8353, 0x0356, 0x035c, 0x8359, 0x0348, 0x834d, 0x8347, 0x0342, + 0x03c0, 0x83c5, 0x83cf, 0x03ca, 0x83db, 0x03de, 0x03d4, 0x83d1, + 0x83f3, 0x03f6, 0x03fc, 0x83f9, 0x03e8, 0x83ed, 0x83e7, 0x03e2, + 0x83a3, 0x03a6, 0x03ac, 0x83a9, 0x03b8, 0x83bd, 0x83b7, 0x03b2, + 0x0390, 0x8395, 0x839f, 0x039a, 0x838b, 0x038e, 0x0384, 0x8381, + + 0x0280, 0x8285, 0x828f, 0x028a, 0x829b, 0x029e, 0x0294, 0x8291, + 0x82b3, 0x02b6, 0x02bc, 0x82b9, 0x02a8, 0x82ad, 0x82a7, 0x02a2, + 0x82e3, 0x02e6, 0x02ec, 0x82e9, 0x02f8, 0x82fd, 0x82f7, 0x02f2, + 0x02d0, 0x82d5, 0x82df, 0x02da, 0x82cb, 0x02ce, 0x02c4, 0x82c1, + 0x8243, 0x0246, 0x024c, 0x8249, 0x0258, 0x825d, 0x8257, 0x0252, + 0x0270, 0x8275, 0x827f, 0x027a, 0x826b, 0x026e, 0x0264, 0x8261, + 0x0220, 0x8225, 0x822f, 0x022a, 0x823b, 0x023e, 0x0234, 0x8231, + 0x8213, 0x0216, 0x021c, 0x8219, 0x0208, 0x820d, 0x8207, 0x0202 +}; + +# define CRC_POLY 0x8005 + +/* + * NAME: bit->init() + * DESCRIPTION: initialize bit pointer struct + */ +void mad_bit_init(struct mad_bitptr *bitptr, unsigned char const *byte) +{ + bitptr->byte = byte; + bitptr->cache = 0; + bitptr->left = CHAR_BIT; +} + +/* + * NAME: bit->length() + * DESCRIPTION: return number of bits between start and end points + */ +unsigned int mad_bit_length(struct mad_bitptr const *begin, + struct mad_bitptr const *end) +{ + return begin->left + + CHAR_BIT * (end->byte - (begin->byte + 1)) + (CHAR_BIT - end->left); +} + +/* + * NAME: bit->nextbyte() + * DESCRIPTION: return pointer to next unprocessed byte + */ +unsigned char const *mad_bit_nextbyte(struct mad_bitptr const *bitptr) +{ + return bitptr->left == CHAR_BIT ? bitptr->byte : bitptr->byte + 1; +} + +/* + * NAME: bit->skip() + * DESCRIPTION: advance bit pointer + */ +void mad_bit_skip(struct mad_bitptr *bitptr, unsigned int len) +{ + bitptr->byte += len / CHAR_BIT; + bitptr->left -= len % CHAR_BIT; + + if (bitptr->left > CHAR_BIT) { + bitptr->byte++; + bitptr->left += CHAR_BIT; + } + + if (bitptr->left < CHAR_BIT) + bitptr->cache = *bitptr->byte; +} + +/* + * NAME: bit->read() + * DESCRIPTION: read an arbitrary number of bits and return their UIMSBF value + */ +unsigned long mad_bit_read(struct mad_bitptr *bitptr, unsigned int len) +{ + register unsigned long value; + + if (bitptr->left == CHAR_BIT) + bitptr->cache = *bitptr->byte; + + if (len < bitptr->left) { + value = (bitptr->cache & ((1 << bitptr->left) - 1)) >> + (bitptr->left - len); + bitptr->left -= len; + + return value; + } + + /* remaining bits in current byte */ + + value = bitptr->cache & ((1 << bitptr->left) - 1); + len -= bitptr->left; + + bitptr->byte++; + bitptr->left = CHAR_BIT; + + /* more bytes */ + + while (len >= CHAR_BIT) { + value = (value << CHAR_BIT) | *bitptr->byte++; + len -= CHAR_BIT; + } + + if (len > 0) { + bitptr->cache = *bitptr->byte; + + value = (value << len) | (bitptr->cache >> (CHAR_BIT - len)); + bitptr->left -= len; + } + + return value; +} + +# if 0 +/* + * NAME: bit->write() + * DESCRIPTION: write an arbitrary number of bits + */ +void mad_bit_write(struct mad_bitptr *bitptr, unsigned int len, + unsigned long value) +{ + unsigned char *ptr; + + ptr = (unsigned char *) bitptr->byte; + + /* ... */ +} +# endif + +/* + * NAME: bit->crc() + * DESCRIPTION: compute CRC-check word + */ +unsigned short mad_bit_crc(struct mad_bitptr bitptr, unsigned int len, + unsigned short init) +{ + register unsigned int crc; + + for (crc = init; len >= 32; len -= 32) { + register unsigned long data; + + data = mad_bit_read(&bitptr, 32); + + crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 24)) & 0xff]; + crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 16)) & 0xff]; + crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 8)) & 0xff]; + crc = (crc << 8) ^ crc_table[((crc >> 8) ^ (data >> 0)) & 0xff]; + } + + switch (len / 8) { + case 3: crc = (crc << 8) ^ + crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff]; + case 2: crc = (crc << 8) ^ + crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff]; + case 1: crc = (crc << 8) ^ + crc_table[((crc >> 8) ^ mad_bit_read(&bitptr, 8)) & 0xff]; + + len %= 8; + + case 0: break; + } + + while (len--) { + register unsigned int msb; + + msb = mad_bit_read(&bitptr, 1) ^ (crc >> 15); + + crc <<= 1; + if (msb & 1) + crc ^= CRC_POLY; + } + + return crc & 0xffff; +} |