Mercurial > repos > blastem

changeset 2554:76259d246695

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Fix YM2612 channel accumulator precision
author Michael Pavone <pavone@retrodev.com>
date Sat, 11 Jan 2025 17:58:58 -0800
parents 35f765c2bc87
children 78e1769efcdb
files ym2612.c
diffstat 1 files changed, 13 insertions(+), 13 deletions(-) [+]
line wrap: on
line diff
--- a/ym2612.c	Sat Jan 11 17:35:15 2025 -0800
+++ b/ym2612.c	Sat Jan 11 17:58:58 2025 -0800
@@ -585,11 +585,16 @@
 		//Update the channel output if we've updated all operators
 		if (op % 4 == 3) {
 			if (chan->algorithm < 4) {
-				chan->output = operator->output;
+				chan->output = operator->output & ~0x1F;
 				chan->phase_overflow = operator->phase_overflow;
 			} else if(chan->algorithm == 4) {
 				ym_operator *other_op = context->operators + channel * 4 + 2;
-				chan->output = operator->output + other_op->output;
+				chan->output = (operator->output & ~0x1F) + (other_op->output & ~0x1F);
+				if (chan->output > 0x1FE0) {
+					chan->output = 0x1FE0;
+				} else if (chan->output < -0x1FF0) {
+					chan->output = - 0x1FF0;
+				}
 				if (operator->phase_inc < other_op->phase_inc) {
 					chan->phase_overflow = operator->phase_overflow;
 				} else {
@@ -599,7 +604,12 @@
 				output = 0;
 				uint32_t lowest_phase_inc = 0xFFFFFFFF;
 				for (uint32_t op = ((chan->algorithm == 7) ? 0 : 1) + channel*4; op < (channel+1)*4; op++) {
-					output += context->operators[op].output;
+					output += context->operators[op].output & ~0x1F;
+					if (output > 0x1FE0) {
+						output = 0x1FE0;
+					} else if (output < -0x1FF0) {
+						output = - 0x1FF0;
+					}
 					if (context->operators[op].phase_inc < lowest_phase_inc) {
 						lowest_phase_inc = context->operators[op].phase_inc;
 						chan->phase_overflow = context->operators[op].phase_overflow;
@@ -617,16 +627,6 @@
 	int16_t left = 0, right = 0;
 	for (int i = 0; i < NUM_CHANNELS; i++) {
 		int16_t value = context->channels[i].output;
-		if (value > 0x1FE0) {
-			value = 0x1FE0;
-		} else if (value < -0x1FF0) {
-			value = -0x1FF0;
-		} else {
-			value &= 0x3FE0;
-			if (value & 0x2000) {
-				value |= 0xC000;
-			}
-		}
 		if (value >= 0) {
 			value += context->zero_offset;
 		} else {