Set FPU mode to round toward zero for mixing

2 files changed, 20 insertions, 1 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index 404dea66..4454b8d4 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -650,9 +650,20 @@ ALvoid aluMixData(ALCcontext *ALContext,ALvoid *buffer,ALsizei size,ALenum forma
     ALuint loop;
     ALint64 DataSize64,DataPos64;
     FILTER *Filter;
+    int fpuState;
 
     SuspendContext(ALContext);
 
+#if defined(HAVE_FESETROUND)
+    fpuState = fegetround();
+    fesetround(FE_TOWARDZERO);
+#elif defined(HAVE__CONTROLFP)
+    fpuState = _controlfp(0, 0);
+    _controlfp(_RC_CHOP, _MCW_RC);
+#else
+    (void)fpuState;
+#endif
+
     //Figure output format variables
     BlockAlign  = aluChannelsFromFormat(format);
     BlockAlign *= aluBytesFromFormat(format);
@@ -1206,5 +1217,11 @@ ALvoid aluMixData(ALCcontext *ALContext,ALvoid *buffer,ALsizei size,ALenum forma
         size -= SamplesToDo;
     }
 
+#if defined(HAVE_FESETROUND)
+    fesetround(fpuState);
+#elif defined(HAVE__CONTROLFP)
+    _controlfp(fpuState, 0xfffff);
+#endif
+
     ProcessContext(ALContext);
 }
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 870edb0b..4ed1f898 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -112,10 +112,12 @@ ENDIF()
 
 CHECK_LIBRARY_EXISTS(m  sqrtf  "" HAVE_SQRTF)
 CHECK_LIBRARY_EXISTS(m  acosf  "" HAVE_ACOSF)
-IF(HAVE_SQRTF OR HAVE_ACOSF)
+CHECK_LIBRARY_EXISTS(m  fesetround  "" HAVE_FESETROUND)
+IF(HAVE_SQRTF OR HAVE_ACOSF OR HAVE_FESETROUND)
     SET(EXTRA_LIBS m ${EXTRA_LIBS})
 ENDIF()
 CHECK_FUNCTION_EXISTS(strtof HAVE_STRTOF)
+CHECK_FUNCTION_EXISTS(_controlfp HAVE__CONTROLFP)
 
 CHECK_FUNCTION_EXISTS(strcasecmp HAVE_STRCASECMP)
 IF(NOT HAVE_STRCASECMP)