# HG changeset patch
# User Sam Lantinga <slouken@libsdl.org>
# Date 1159112737 0
# Node ID 74e828c64315937d5923c40c36e2d932ea48daf3
# Parent  c82c1870c77a8518fa32e55dd0392aaff3b784ee
Fixed bug #292

I might be on crack here.

It looks like SDL_ConvertMono() in src/audio/SDL_audiocvt.c adds the left and
right channels of a stereo stream together, and clamps the new mono channel if
it would overflow.

Shouldn't it be dividing by 2 to average the two sample points instead of
clamping? Otherwise the mono sample point's volume doubles in the conversion.
This would also make the conversion faster, as it replaces two branches per
sample frame with a bitwise shift.

--ryan.

diff -r c82c1870c77a -r 74e828c64315 src/audio/SDL_audiocvt.c
--- a/src/audio/SDL_audiocvt.c	Sun Sep 24 15:36:37 2006 +0000
+++ b/src/audio/SDL_audiocvt.c	Sun Sep 24 15:45:37 2006 +0000
@@ -44,11 +44,7 @@
 			dst = cvt->buf;
 			for ( i=cvt->len_cvt/2; i; --i ) {
 				sample = src[0] + src[1];
-				if ( sample > 255 ) {
-					*dst = 255;
-				} else {
-					*dst = (Uint8)sample;
-				}
+				*dst = (Uint8)(sample / 2);
 				src += 2;
 				dst += 1;
 			}
@@ -62,14 +58,7 @@
 			dst = (Sint8 *)cvt->buf;
 			for ( i=cvt->len_cvt/2; i; --i ) {
 				sample = src[0] + src[1];
-				if ( sample > 127 ) {
-					*dst = 127;
-				} else
-				if ( sample < -128 ) {
-					*dst = -128;
-				} else {
-					*dst = (Sint8)sample;
-				}
+				*dst = (Sint8)(sample / 2);
 				src += 2;
 				dst += 1;
 			}
@@ -85,14 +74,10 @@
 				for ( i=cvt->len_cvt/4; i; --i ) {
 					sample = (Uint16)((src[0]<<8)|src[1])+
 					         (Uint16)((src[2]<<8)|src[3]);
-					if ( sample > 65535 ) {
-						dst[0] = 0xFF;
-						dst[1] = 0xFF;
-					} else {
-						dst[1] = (sample&0xFF);
-						sample >>= 8;
-						dst[0] = (sample&0xFF);
-					}
+					sample /= 2;
+					dst[1] = (sample&0xFF);
+					sample >>= 8;
+					dst[0] = (sample&0xFF);
 					src += 4;
 					dst += 2;
 				}
@@ -100,14 +85,10 @@
 				for ( i=cvt->len_cvt/4; i; --i ) {
 					sample = (Uint16)((src[1]<<8)|src[0])+
 					         (Uint16)((src[3]<<8)|src[2]);
-					if ( sample > 65535 ) {
-						dst[0] = 0xFF;
-						dst[1] = 0xFF;
-					} else {
-						dst[0] = (sample&0xFF);
-						sample >>= 8;
-						dst[1] = (sample&0xFF);
-					}
+					sample /= 2;
+					dst[0] = (sample&0xFF);
+					sample >>= 8;
+					dst[1] = (sample&0xFF);
 					src += 4;
 					dst += 2;
 				}
@@ -124,18 +105,10 @@
 				for ( i=cvt->len_cvt/4; i; --i ) {
 					sample = (Sint16)((src[0]<<8)|src[1])+
 					         (Sint16)((src[2]<<8)|src[3]);
-					if ( sample > 32767 ) {
-						dst[0] = 0x7F;
-						dst[1] = 0xFF;
-					} else
-					if ( sample < -32768 ) {
-						dst[0] = 0x80;
-						dst[1] = 0x00;
-					} else {
-						dst[1] = (sample&0xFF);
-						sample >>= 8;
-						dst[0] = (sample&0xFF);
-					}
+					sample /= 2;
+					dst[1] = (sample&0xFF);
+					sample >>= 8;
+					dst[0] = (sample&0xFF);
 					src += 4;
 					dst += 2;
 				}
@@ -143,18 +116,10 @@
 				for ( i=cvt->len_cvt/4; i; --i ) {
 					sample = (Sint16)((src[1]<<8)|src[0])+
 					         (Sint16)((src[3]<<8)|src[2]);
-					if ( sample > 32767 ) {
-						dst[1] = 0x7F;
-						dst[0] = 0xFF;
-					} else
-					if ( sample < -32768 ) {
-						dst[1] = 0x80;
-						dst[0] = 0x00;
-					} else {
-						dst[0] = (sample&0xFF);
-						sample >>= 8;
-						dst[1] = (sample&0xFF);
-					}
+					sample /= 2;
+					dst[0] = (sample&0xFF);
+					sample >>= 8;
+					dst[1] = (sample&0xFF);
 					src += 4;
 					dst += 2;
 				}