# HG changeset patch
# User Sam Lantinga <slouken@libsdl.org>
# Date 1159113396 0
# Node ID 3908e1f808e14fadb8a8db536c11a5acccea5d70
# Parent  4a32d186f35bdd0a7a66dda024a028472f518f70
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 4a32d186f35b -r 3908e1f808e1 src/audio/SDL_audiocvt.c
--- a/src/audio/SDL_audiocvt.c	Sun Sep 24 00:55:19 2006 +0000
+++ b/src/audio/SDL_audiocvt.c	Sun Sep 24 15:56:36 2006 +0000
@@ -45,11 +45,7 @@
             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;
             }
@@ -64,13 +60,7 @@
             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;
             }
@@ -87,14 +77,10 @@
                 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;
                 }
@@ -102,14 +88,10 @@
                 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;
                 }
@@ -127,17 +109,10 @@
                 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;
                 }
@@ -145,17 +120,10 @@
                 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;
                 }