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Fix 12-bit wrapping behavior in YM2608/2610 ADPCM_A decoding, fixes some glitches in certain samples in the metal slug series, and likely other games. [Lord Nightmare, madbr]

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This commit is contained in:
Lord-Nightmare 2019-04-04 06:44:43 -04:00
parent b7a49aff4a
commit f746588771
1 changed files with 4 additions and 3 deletions
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7
src/devices/sound/fm.cpp
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@ -2499,11 +2499,12 @@ struct ym2610_state
ch->adpcm_acc += jedi_table[ch->adpcm_step + data]; ch->adpcm_acc += jedi_table[ch->adpcm_step + data];
/* the 12-bit accumulator wraps on the ym2610 and ym2608 (like the msm5205), it does not saturate (like the msm5218) */
ch->adpcm_acc &= 0xfff;
/* extend 12-bit signed int */ /* extend 12-bit signed int */
if (ch->adpcm_acc & ~0x7ff) if (ch->adpcm_acc & 0x800)
ch->adpcm_acc |= ~0xfff; ch->adpcm_acc |= ~0xfff;
else
ch->adpcm_acc &= 0xfff;
ch->adpcm_step += step_inc[data & 7]; ch->adpcm_step += step_inc[data & 7];
Limit( ch->adpcm_step, 48*16, 0*16 ); Limit( ch->adpcm_step, 48*16, 0*16 );