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* libmad - MPEG audio decoder library
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* Copyright (C) 2000-2004 Underbit Technologies, Inc.
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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* $Id: layer12.c,v 1.17 2004/02/05 09:02:39 rob Exp $
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* used in both Layer I and Layer II decoding
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mad_fixed_t const sf_table[64] = {
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# include "sf_table.dat"
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/* --- Layer I ------------------------------------------------------------- */
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/* linear scaling table */
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mad_fixed_t const linear_table[14] = {
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MAD_F(0x15555555), /* 2^2 / (2^2 - 1) == 1.33333333333333 */
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MAD_F(0x12492492), /* 2^3 / (2^3 - 1) == 1.14285714285714 */
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MAD_F(0x11111111), /* 2^4 / (2^4 - 1) == 1.06666666666667 */
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MAD_F(0x10842108), /* 2^5 / (2^5 - 1) == 1.03225806451613 */
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MAD_F(0x10410410), /* 2^6 / (2^6 - 1) == 1.01587301587302 */
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MAD_F(0x10204081), /* 2^7 / (2^7 - 1) == 1.00787401574803 */
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MAD_F(0x10101010), /* 2^8 / (2^8 - 1) == 1.00392156862745 */
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MAD_F(0x10080402), /* 2^9 / (2^9 - 1) == 1.00195694716243 */
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MAD_F(0x10040100), /* 2^10 / (2^10 - 1) == 1.00097751710655 */
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MAD_F(0x10020040), /* 2^11 / (2^11 - 1) == 1.00048851978505 */
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MAD_F(0x10010010), /* 2^12 / (2^12 - 1) == 1.00024420024420 */
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MAD_F(0x10008004), /* 2^13 / (2^13 - 1) == 1.00012208521548 */
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MAD_F(0x10004001), /* 2^14 / (2^14 - 1) == 1.00006103888177 */
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MAD_F(0x10002000) /* 2^15 / (2^15 - 1) == 1.00003051850948 */
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* DESCRIPTION: decode one requantized Layer I sample from a bitstream
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mad_fixed_t I_sample(struct mad_bitptr *ptr, unsigned int nb)
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sample = mad_bit_read(ptr, nb);
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/* invert most significant bit, extend sign, then scale to fixed format */
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sample ^= 1 << (nb - 1);
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sample |= -(sample & (1 << (nb - 1)));
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sample <<= MAD_F_FRACBITS - (nb - 1);
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/* requantize the sample */
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/* s'' = (2^nb / (2^nb - 1)) * (s''' + 2^(-nb + 1)) */
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sample += MAD_F_ONE >> (nb - 1);
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return mad_f_mul(sample, linear_table[nb - 2]);
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/* s' = factor * s'' */
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/* (to be performed by caller) */
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* DESCRIPTION: decode a single Layer I frame
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int mad_layer_I(struct mad_stream *stream, struct mad_frame *frame)
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struct mad_header *header = &frame->header;
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unsigned int nch, bound, ch, s, sb, nb;
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unsigned char allocation[2][32], scalefactor[2][32];
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nch = MAD_NCHANNELS(header);
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if (header->mode == MAD_MODE_JOINT_STEREO) {
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header->flags |= MAD_FLAG_I_STEREO;
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bound = 4 + header->mode_extension * 4;
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if (header->flags & MAD_FLAG_PROTECTION) {
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mad_bit_crc(stream->ptr, 4 * (bound * nch + (32 - bound)),
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if (header->crc_check != header->crc_target &&
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!(frame->options & MAD_OPTION_IGNORECRC)) {
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stream->error = MAD_ERROR_BADCRC;
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/* decode bit allocations */
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for (sb = 0; sb < bound; ++sb) {
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for (ch = 0; ch < nch; ++ch) {
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nb = mad_bit_read(&stream->ptr, 4);
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stream->error = MAD_ERROR_BADBITALLOC;
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allocation[ch][sb] = nb ? nb + 1 : 0;
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for (sb = bound; sb < 32; ++sb) {
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nb = mad_bit_read(&stream->ptr, 4);
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stream->error = MAD_ERROR_BADBITALLOC;
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allocation[1][sb] = nb ? nb + 1 : 0;
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/* decode scalefactors */
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for (sb = 0; sb < 32; ++sb) {
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for (ch = 0; ch < nch; ++ch) {
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if (allocation[ch][sb]) {
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scalefactor[ch][sb] = mad_bit_read(&stream->ptr, 6);
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# if defined(OPT_STRICT)
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* Scalefactor index 63 does not appear in Table B.1 of
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* ISO/IEC 11172-3. Nonetheless, other implementations accept it,
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* so we only reject it if OPT_STRICT is defined.
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if (scalefactor[ch][sb] == 63) {
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stream->error = MAD_ERROR_BADSCALEFACTOR;
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for (s = 0; s < 12; ++s) {
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for (sb = 0; sb < bound; ++sb) {
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for (ch = 0; ch < nch; ++ch) {
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nb = allocation[ch][sb];
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frame->sbsample[ch][s][sb] = nb ?
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mad_f_mul(I_sample(&stream->ptr, nb),
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sf_table[scalefactor[ch][sb]]) : 0;
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for (sb = bound; sb < 32; ++sb) {
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if ((nb = allocation[0][sb])) {
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sample = I_sample(&stream->ptr, nb);
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for (ch = 0; ch < nch; ++ch) {
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frame->sbsample[ch][s][sb] =
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mad_f_mul(sample, sf_table[scalefactor[ch][sb]]);
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for (ch = 0; ch < nch; ++ch)
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frame->sbsample[ch][s][sb] = 0;
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/* --- Layer II ------------------------------------------------------------ */
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/* possible quantization per subband table */
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unsigned int sblimit;
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unsigned char const offsets[30];
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} const sbquant_table[5] = {
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/* ISO/IEC 11172-3 Table B.2a */
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{ 27, { 7, 7, 7, 6, 6, 6, 6, 6, 6, 6, 6, 3, 3, 3, 3, 3, /* 0 */
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3, 3, 3, 3, 3, 3, 3, 0, 0, 0, 0 } },
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/* ISO/IEC 11172-3 Table B.2b */
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{ 30, { 7, 7, 7, 6, 6, 6, 6, 6, 6, 6, 6, 3, 3, 3, 3, 3, /* 1 */
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3, 3, 3, 3, 3, 3, 3, 0, 0, 0, 0, 0, 0, 0 } },
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/* ISO/IEC 11172-3 Table B.2c */
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{ 8, { 5, 5, 2, 2, 2, 2, 2, 2 } }, /* 2 */
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/* ISO/IEC 11172-3 Table B.2d */
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{ 12, { 5, 5, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2 } }, /* 3 */
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/* ISO/IEC 13818-3 Table B.1 */
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{ 30, { 4, 4, 4, 4, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, /* 4 */
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1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 } }
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/* bit allocation table */
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unsigned short offset;
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} const bitalloc_table[8] = {
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/* offsets into quantization class table */
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unsigned char const offset_table[6][15] = {
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{ 0, 1, 16 }, /* 0 */
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{ 0, 1, 2, 3, 4, 5, 16 }, /* 1 */
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{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 }, /* 2 */
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{ 0, 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 }, /* 3 */
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{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16 }, /* 4 */
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{ 0, 2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 } /* 5 */
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/* quantization class table */
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unsigned short nlevels;
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} const qc_table[17] = {
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# include "qc_table.dat"
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* DESCRIPTION: decode three requantized Layer II samples from a bitstream
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void II_samples(struct mad_bitptr *ptr,
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struct quantclass const *quantclass,
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mad_fixed_t output[3])
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unsigned int nb, s, sample[3];
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if ((nb = quantclass->group)) {
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unsigned int c, nlevels;
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c = mad_bit_read(ptr, quantclass->bits);
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nlevels = quantclass->nlevels;
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for (s = 0; s < 3; ++s) {
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sample[s] = c % nlevels;
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nb = quantclass->bits;
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for (s = 0; s < 3; ++s)
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sample[s] = mad_bit_read(ptr, nb);
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for (s = 0; s < 3; ++s) {
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mad_fixed_t requantized;
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/* invert most significant bit, extend sign, then scale to fixed format */
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requantized = sample[s] ^ (1 << (nb - 1));
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requantized |= -(requantized & (1 << (nb - 1)));
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requantized <<= MAD_F_FRACBITS - (nb - 1);
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/* requantize the sample */
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/* s'' = C * (s''' + D) */
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output[s] = mad_f_mul(requantized + quantclass->D, quantclass->C);
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/* s' = factor * s'' */
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/* (to be performed by caller) */
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* DESCRIPTION: decode a single Layer II frame
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int mad_layer_II(struct mad_stream *stream, struct mad_frame *frame)
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struct mad_header *header = &frame->header;
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struct mad_bitptr start;
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unsigned int index, sblimit, nbal, nch, bound, gr, ch, s, sb;
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unsigned char const *offsets;
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unsigned char allocation[2][32], scfsi[2][32], scalefactor[2][32][3];
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mad_fixed_t samples[3];
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nch = MAD_NCHANNELS(header);
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if (header->flags & MAD_FLAG_LSF_EXT)
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else if (header->flags & MAD_FLAG_FREEFORMAT)
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unsigned long bitrate_per_channel;
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bitrate_per_channel = header->bitrate;
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bitrate_per_channel /= 2;
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# if defined(OPT_STRICT)
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* ISO/IEC 11172-3 allows only single channel mode for 32, 48, 56, and
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* 80 kbps bitrates in Layer II, but some encoders ignore this
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* restriction. We enforce it if OPT_STRICT is defined.
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if (bitrate_per_channel <= 28000 || bitrate_per_channel == 40000) {
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stream->error = MAD_ERROR_BADMODE;
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else { /* nch == 1 */
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if (bitrate_per_channel > 192000) {
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* ISO/IEC 11172-3 does not allow single channel mode for 224, 256,
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* 320, or 384 kbps bitrates in Layer II.
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stream->error = MAD_ERROR_BADMODE;
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if (bitrate_per_channel <= 48000)
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index = (header->samplerate == 32000) ? 3 : 2;
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else if (bitrate_per_channel <= 80000)
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index = (header->samplerate == 48000) ? 0 : 1;
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sblimit = sbquant_table[index].sblimit;
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offsets = sbquant_table[index].offsets;
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if (header->mode == MAD_MODE_JOINT_STEREO) {
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header->flags |= MAD_FLAG_I_STEREO;
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bound = 4 + header->mode_extension * 4;
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/* decode bit allocations */
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for (sb = 0; sb < bound; ++sb) {
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nbal = bitalloc_table[offsets[sb]].nbal;
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for (ch = 0; ch < nch; ++ch)
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allocation[ch][sb] = mad_bit_read(&stream->ptr, nbal);
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for (sb = bound; sb < sblimit; ++sb) {
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nbal = bitalloc_table[offsets[sb]].nbal;
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allocation[1][sb] = mad_bit_read(&stream->ptr, nbal);
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/* decode scalefactor selection info */
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for (sb = 0; sb < sblimit; ++sb) {
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for (ch = 0; ch < nch; ++ch) {
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if (allocation[ch][sb])
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scfsi[ch][sb] = mad_bit_read(&stream->ptr, 2);
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if (header->flags & MAD_FLAG_PROTECTION) {
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mad_bit_crc(start, mad_bit_length(&start, &stream->ptr),
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if (header->crc_check != header->crc_target &&
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!(frame->options & MAD_OPTION_IGNORECRC)) {
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stream->error = MAD_ERROR_BADCRC;
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/* decode scalefactors */
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for (sb = 0; sb < sblimit; ++sb) {
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for (ch = 0; ch < nch; ++ch) {
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if (allocation[ch][sb]) {
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scalefactor[ch][sb][0] = mad_bit_read(&stream->ptr, 6);
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switch (scfsi[ch][sb]) {
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scalefactor[ch][sb][2] =
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scalefactor[ch][sb][1] =
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scalefactor[ch][sb][0];
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scalefactor[ch][sb][1] = mad_bit_read(&stream->ptr, 6);
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scalefactor[ch][sb][2] = mad_bit_read(&stream->ptr, 6);
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if (scfsi[ch][sb] & 1)
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scalefactor[ch][sb][1] = scalefactor[ch][sb][scfsi[ch][sb] - 1];
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# if defined(OPT_STRICT)
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* Scalefactor index 63 does not appear in Table B.1 of
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* ISO/IEC 11172-3. Nonetheless, other implementations accept it,
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* so we only reject it if OPT_STRICT is defined.
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if (scalefactor[ch][sb][0] == 63 ||
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scalefactor[ch][sb][1] == 63 ||
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scalefactor[ch][sb][2] == 63) {
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stream->error = MAD_ERROR_BADSCALEFACTOR;
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for (gr = 0; gr < 12; ++gr) {
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for (sb = 0; sb < bound; ++sb) {
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for (ch = 0; ch < nch; ++ch) {
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if ((index = allocation[ch][sb])) {
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index = offset_table[bitalloc_table[offsets[sb]].offset][index - 1];
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II_samples(&stream->ptr, &qc_table[index], samples);
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for (s = 0; s < 3; ++s) {
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frame->sbsample[ch][3 * gr + s][sb] =
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mad_f_mul(samples[s], sf_table[scalefactor[ch][sb][gr / 4]]);
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for (s = 0; s < 3; ++s)
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frame->sbsample[ch][3 * gr + s][sb] = 0;
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for (sb = bound; sb < sblimit; ++sb) {
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if ((index = allocation[0][sb])) {
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index = offset_table[bitalloc_table[offsets[sb]].offset][index - 1];
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II_samples(&stream->ptr, &qc_table[index], samples);
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for (ch = 0; ch < nch; ++ch) {
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for (s = 0; s < 3; ++s) {
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frame->sbsample[ch][3 * gr + s][sb] =
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mad_f_mul(samples[s], sf_table[scalefactor[ch][sb][gr / 4]]);
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for (ch = 0; ch < nch; ++ch) {
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for (s = 0; s < 3; ++s)
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frame->sbsample[ch][3 * gr + s][sb] = 0;
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for (ch = 0; ch < nch; ++ch) {
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for (s = 0; s < 3; ++s) {
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for (sb = sblimit; sb < 32; ++sb)
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frame->sbsample[ch][3 * gr + s][sb] = 0;
added
removed
src/libmad/layer12.c
