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changeset 3880:74e828c64315 SDL-1.2

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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.
author Sam Lantinga <slouken@libsdl.org>
date Sun, 24 Sep 2006 15:45:37 +0000
parents c82c1870c77a
children c1b6bb5205f1
files src/audio/SDL_audiocvt.c
diffstat 1 files changed, 18 insertions(+), 53 deletions(-) [+]
line wrap: on
line diff
--- 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;
 				}