mirror of
https://github.com/RaySollium99/picodrive.git
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120 lines
3 KiB
C
120 lines
3 KiB
C
/*
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* PicoDrive
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* (C) notaz, 2008
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*
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* This work is licensed under the terms of MAME license.
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* See COPYING file in the top-level directory.
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*
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* The following ADPCM algorithm was stolen from MAME aica driver.
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* I'm quite sure it's not the right one, but it's the
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* best sounding of the ones that I tried.
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*/
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#include "../pico_int.h"
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#define ADPCMSHIFT 8
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#define ADFIX(f) (int) ((double)f * (double)(1<<ADPCMSHIFT))
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/* limitter */
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#define Limit(val, max, min) { \
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if ( val > max ) val = max; \
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else if ( val < min ) val = min; \
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}
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static const int TableQuant[8] =
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{
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ADFIX(0.8984375),
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ADFIX(0.8984375),
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ADFIX(0.8984375),
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ADFIX(0.8984375),
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ADFIX(1.19921875),
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ADFIX(1.59765625),
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ADFIX(2.0),
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ADFIX(2.3984375)
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};
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// changed using trial and error..
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//static const int quant_mul[16] = { 1, 3, 5, 7, 9, 11, 13, 15, -1, -3, -5, -7, -9, -11, -13, -15 };
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static const int quant_mul[16] = { 1, 3, 5, 7, 9, 11, 13, -1, -1, -3, -5, -7, -9, -11, -13, -15 };
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static int sample = 0, quant = 0, sgn = 0;
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static int stepsamples = (44100<<10)/16000;
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PICO_INTERNAL void PicoPicoPCMReset(void)
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{
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sample = sgn = 0;
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quant = 0x7f;
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memset(PicoPicohw.xpcm_buffer, 0, sizeof(PicoPicohw.xpcm_buffer));
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}
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PICO_INTERNAL void PicoPicoPCMRerate(int xpcm_rate)
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{
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stepsamples = (PicoIn.sndRate<<10)/xpcm_rate;
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}
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#define XSHIFT 6
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#define do_sample() \
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{ \
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int delta = quant * quant_mul[srcval] >> XSHIFT; \
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sample += delta - (delta >> 2); /* 3/4 */ \
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quant = (quant * TableQuant[srcval&7]) >> ADPCMSHIFT; \
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Limit(quant, 0x6000, 0x7f); \
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Limit(sample, 32767*3/4, -32768*3/4); \
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}
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PICO_INTERNAL void PicoPicoPCMUpdate(short *buffer, int length, int stereo)
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{
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unsigned char *src = PicoPicohw.xpcm_buffer;
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unsigned char *lim = PicoPicohw.xpcm_ptr;
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int srcval, needsamples = 0;
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if (src == lim) goto end;
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for (; length > 0 && src < lim; src++)
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{
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srcval = *src >> 4;
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do_sample();
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for (needsamples += stepsamples; needsamples > (1<<10) && length > 0; needsamples -= (1<<10), length--) {
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*buffer++ += sample;
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if (stereo) { buffer[0] = buffer[-1]; buffer++; }
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}
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srcval = *src & 0xf;
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do_sample();
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for (needsamples += stepsamples; needsamples > (1<<10) && length > 0; needsamples -= (1<<10), length--) {
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*buffer++ += sample;
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if (stereo) { buffer[0] = buffer[-1]; buffer++; }
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}
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// lame normalization stuff, needed due to wrong adpcm algo
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sgn += (sample < 0) ? -1 : 1;
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if (sgn < -16 || sgn > 16) sample -= sample >> 5;
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}
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if (src < lim) {
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int di = lim - src;
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memmove(PicoPicohw.xpcm_buffer, src, di);
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PicoPicohw.xpcm_ptr = PicoPicohw.xpcm_buffer + di;
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elprintf(EL_PICOHW, "xpcm update: over %i", di);
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// adjust fifo
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PicoPicohw.fifo_bytes = di;
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return;
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}
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elprintf(EL_PICOHW, "xpcm update: under %i", length);
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PicoPicohw.xpcm_ptr = PicoPicohw.xpcm_buffer;
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end:
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if (stereo)
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// still must expand SN76496 to stereo
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for (; length > 0; buffer+=2, length--)
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buffer[1] = buffer[0];
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sample = sgn = 0;
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quant = 0x7f;
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}
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