63 lines
1.9 KiB
C
63 lines
1.9 KiB
C
#include "coding.h"
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#include "../util.h"
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/* tweaked XA/PSX coefs << 6 */
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static const short lsf_coefs[16][2] = {
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{ 115, -52 },
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{ 0, 0 },
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{ 98, -55 },
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{ 60, 0 },
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{ 122, -60 },
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/* rest assumed to be 0s */
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};
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void decode_lsf(VGMSTREAMCHANNEL *stream, sample_t *outbuf, int channelspacing, int32_t first_sample, int32_t samples_to_do) {
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uint8_t frame[0x1c] = {0};
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off_t frame_offset;
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int i, frames_in, sample_count = 0;
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int index, shift, coef1, coef2;
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size_t bytes_per_frame, samples_per_frame;
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int32_t hist1 = stream->adpcm_history1_16;
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int32_t hist2 = stream->adpcm_history2_16;
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uint8_t header;
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/* external interleave (fixed size), mono */
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bytes_per_frame = 0x1c;
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samples_per_frame = (bytes_per_frame - 1) * 2;
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frames_in = first_sample / samples_per_frame;
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//first_sample = first_sample % samples_per_frame; /* for flat layout */
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/* external interleave (fixed size), mono */
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frame_offset = stream->offset + bytes_per_frame * frames_in;
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read_streamfile(frame, frame_offset, bytes_per_frame, stream->streamfile); /* ignore EOF errors */
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header = 0xFF - frame[0x00];
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shift = (header >> 4) & 0xf;
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index = (header >> 0) & 0xf;
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coef1 = lsf_coefs[index][0];
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coef2 = lsf_coefs[index][1];
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/* decode nibbles */
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for (i = first_sample; i < first_sample + samples_to_do; i++) {
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uint8_t nibbles = frame[0x01 + i/2];
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int32_t sample;
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sample = i&1 ? /* low nibble first */
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get_high_nibble_signed(nibbles) :
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get_low_nibble_signed(nibbles);
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sample = sample * (1 << (12 - shift));
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sample = sample + (hist1 * coef1 + hist2 * coef2) / 64; /* >> 6 */
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sample = clamp16(sample);
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outbuf[sample_count] = sample;
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sample_count += channelspacing;
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hist2 = hist1;
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hist1 = sample;
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}
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stream->adpcm_history1_16 = hist1;
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stream->adpcm_history2_16 = hist2;
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}
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