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51 lines
1.6 KiB
C
51 lines
1.6 KiB
C
#include "../util.h"
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#include "coding.h"
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/* fixed point (.8) amount to scale the current step size by */
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/* part of the same series as used in MS ADPCM "ADPCMTable" */
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static const unsigned int scale_step[16] =
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{
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230, 230, 230, 230, 307, 409, 512, 614,
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230, 230, 230, 230, 307, 409, 512, 614
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};
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/* expand an unsigned four bit delta to a wider signed range */
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static const int scale_delta[16] =
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{
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1, 3, 5, 7, 9, 11, 13, 15,
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-1, -3, -5, -7, -9,-11,-13,-15
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};
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/* Yamaha AICA ADPCM (as seen in Dreamcast) */
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void decode_aica(VGMSTREAMCHANNEL * stream, sample * outbuf, int channelspacing, int32_t first_sample, int32_t samples_to_do) {
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int i;
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int32_t sample_count;
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int32_t hist1 = stream->adpcm_history1_16;
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uint32_t step_size = stream->adpcm_step_index;
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for (i=first_sample,sample_count=0; i<first_sample+samples_to_do; i++,sample_count+=channelspacing) {
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int sample_nibble =
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(
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(unsigned)read_8bit(stream->offset+i/2,stream->streamfile) >>
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(i&1?4:0)
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)&0xf;
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int32_t sample_delta = (int32_t)step_size * scale_delta[sample_nibble];
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int32_t new_sample;
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new_sample = hist1 + sample_delta/8;
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outbuf[sample_count] = clamp16(new_sample);
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hist1 = outbuf[sample_count];
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step_size = (step_size * scale_step[sample_nibble])/0x100;
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if (step_size < 0x7f) step_size = 0x7f;
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if (step_size > 0x6000) step_size = 0x6000;
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}
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stream->adpcm_history1_16 = hist1;
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stream->adpcm_step_index = step_size;
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}
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