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44 lines
1.5 KiB
C
44 lines
1.5 KiB
C
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#include "coding.h"
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/* IMA table plus seven extra steps at the beginning */
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static const int derf_steps[96] = {
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0, 1, 2, 3, 4, 5, 6, 7,
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8, 9, 10, 11, 12, 13, 14, 16,
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17, 19, 21, 23, 25, 28, 31, 34,
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37, 41, 45, 50, 55, 60, 66, 73,
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80, 88, 97, 107, 118, 130, 143, 157,
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173, 190, 209, 230, 253, 279, 307, 337,
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371, 408, 449, 494, 544, 598, 658, 724,
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796, 876, 963, 1060, 1166, 1282, 1411, 1552,
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1707, 1878, 2066, 2272, 2499, 2749, 3024, 3327,
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3660, 4026, 4428, 4871, 5358, 5894, 6484, 7132,
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7845, 8630, 9493, 10442, 11487, 12635, 13899, 15289,
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16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767,
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};
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/* Xilam DERF DPCM for Stupid Invaders (PC), decompiled from the exe */
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void decode_derf(VGMSTREAMCHANNEL * stream, sample * outbuf, int channelspacing, int32_t first_sample, int32_t samples_to_do) {
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int i, sample_pos = 0, index;
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int32_t hist = stream->adpcm_history1_32;
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off_t frame_offset = stream->offset; /* frame size is 1 */
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for(i = first_sample; i < first_sample + samples_to_do; i++) {
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uint8_t code = (uint8_t)read_8bit(frame_offset+i,stream->streamfile);
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/* original exe doesn't clamp the index, so presumably codes can't over it */
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index = code & 0x7f;
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if (index > 95) index = 95;
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if (code & 0x80)
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hist -= derf_steps[index];
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else
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hist += derf_steps[index];
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outbuf[sample_pos] = clamp16(hist);
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sample_pos += channelspacing;
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}
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stream->adpcm_history1_32 = hist;
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}
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