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xa: tweak decoding to be closer to PSX

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bnnm 2021-10-24 10:54:03 +02:00
parent 3e2f7aab75
commit be7e4821d7
1 changed files with 6 additions and 21 deletions
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27
src/coding/xa_decoder.c
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@ -1,25 +1,16 @@
#include "coding.h"
#include "../util.h"
// todo this is based on Kazzuya's old code; different emus (PCSX, Mame, Mednafen, etc) do
// XA coefs int math in different ways (see comments below), not 100% accurate.
// May be implemented like the SNES/SPC700 BRR.
/* XA ADPCM gain values */
//#define XA_FLOAT 1
//#define XA_INTB 1
#if XA_FLOAT
/* floats as defined by the spec, but PS1's SPU would use int math */
static const float K0[4] = { 0.0, 0.9375, 1.796875, 1.53125 };
static const float K1[4] = { 0.0, 0.0, -0.8125, -0.859375 };
#elif XA_INTB
/* K0/1 floats to int, -K*2^6 = -K*(1<<6) = -K*64 */
#else
/* K0/1 floats to int with N=6: K*2^6 = K*(1<<6) = K*64 */
static const int K0[4] = { 0, 60, 115, 98 };
static const int K1[4] = { 0, 0, -52, -55 };
#else
/* K0/1 floats to int, -K*2^10 = -K*(1<<10) = -K*1024 */
static const int K0[4] = { 0, -960, -1840, -1568 };
static const int K1[4] = { 0, 0, 832, 880 };
#endif
/* Sony XA ADPCM, defined for CD-DA/CD-i in the "Red Book" (private) or "Green Book" (public) specs.
@ -105,21 +96,15 @@ static void decode_xa_frame(xa_t* xa, int32_t first_sample, int32_t samples_to_d
sample = (int16_t)((su << 12) & 0xf000) >> shift; /* 16b sign extend + scale */
}
sample = sample << 4; /* scale for K */ //todo bad
#if XA_FLOAT
sample = sample + (coef1 * hist1 + coef2 * hist2);
#elif XA_INTB
sample = sample + ((coef1 * hist1 + coef2 * hist2) >> 6);
sample = sample + (coef1 * xa->hist1 + coef2 * xa->hist2);
#else
sample = sample - ((coef1 * xa->hist1 + coef2 * xa->hist2) >> 10);
sample = sample + ((coef1 * xa->hist1 + coef2 * xa->hist2 + 32) >> 6);
#endif
xa->hist2 = xa->hist1;
xa->hist1 = sample; /* must go before clamp, somehow */
sample = sample >> 4;
sample = clamp16(sample);
xa->sbuf[samples_done * xa->channels] = sample;
xa->hist1 = sample;
xa->sbuf[samples_done * xa->channels] = clamp16(sample); /* don't clamp hist */
samples_done++;
sample_count++;