From 675ed65251ae402c2a4ae1cdd44bf5238cc322a0 Mon Sep 17 00:00:00 2001
From: Sandro Santilli <strk@keybit.net>
Date: Thu, 17 Dec 2015 17:09:02 +0100
Subject: [PATCH] Use LSB or MSB audio mixing based on machine endian

NOTE: only tested on LSB machine
---
 libsound/sound_handler.cpp | 69 ++++++++++++++++++++++++++++++++++------------
 1 file changed, 51 insertions(+), 18 deletions(-)

diff --git a/libsound/sound_handler.cpp b/libsound/sound_handler.cpp
index a39cb6eb3..454a03ef3 100644
--- a/libsound/sound_handler.cpp
+++ b/libsound/sound_handler.cpp
@@ -82,29 +82,62 @@ mixAudio(std::uint8_t *dst, const std::uint8_t *src, std::uint32_t len, int volu
 {
   if ( volume == 0 ) return;
 
-  // AUDIO_S16LSB
+  union {
+    int16_t i;
+    char c[2];
+  } isbig;
+  isbig.i = 1;
+
+  int lsb = ( isbig.c[0] == 1 );
+
   std::int16_t src1, src2;
   int dst_sample;
   const int max_audioval = ((1<<(16-1))-1);
   const int min_audioval = -(1<<(16-1));
 
-  len /= 2;
-  while ( len-- ) {
-    src1 = ((src[1])<<8|src[0]);
-    ADJUST_VOLUME(src1, volume);
-    src2 = ((dst[1])<<8|dst[0]);
-    src += 2;
-    dst_sample = src1+src2;
-    if ( dst_sample > max_audioval ) {
-      dst_sample = max_audioval;
-    } else
-    if ( dst_sample < min_audioval ) {
-      dst_sample = min_audioval;
-    }
-    dst[0] = dst_sample&0xFF;
-    dst_sample >>= 8;
-    dst[1] = dst_sample&0xFF;
-    dst += 2;
+  if ( lsb )
+  {
+    // AUDIO_S16LSB
+    len /= 2;
+    while ( len-- ) {
+      src1 = ((src[1])<<8|src[0]);
+      ADJUST_VOLUME(src1, volume);
+      src2 = ((dst[1])<<8|dst[0]);
+      src += 2;
+      dst_sample = src1+src2;
+      if ( dst_sample > max_audioval ) {
+        dst_sample = max_audioval;
+      } else
+      if ( dst_sample < min_audioval ) {
+        dst_sample = min_audioval;
+      }
+      dst[0] = dst_sample&0xFF;
+      dst_sample >>= 8;
+      dst[1] = dst_sample&0xFF;
+      dst += 2;
+    }
+  }
+  else
+  {
+    // AUDIO_S16MSB
+    len /= 2;
+    while ( len-- ) {
+      src1 = ((src[0])<<8|src[1]);
+      ADJUST_VOLUME(src1, volume);
+      src2 = ((dst[0])<<8|dst[1]);
+      src += 2;
+      dst_sample = src1+src2;
+      if ( dst_sample > max_audioval ) {
+        dst_sample = max_audioval;
+      } else
+      if ( dst_sample < min_audioval ) {
+        dst_sample = min_audioval;
+      }
+      dst[1] = dst_sample&0xFF;
+      dst_sample >>= 8;
+      dst[0] = dst_sample&0xFF;
+      dst += 2;
+    }
   }
 }
 
-- 
2.11.4.GIT