Fix overflow issues when converting float to int

32-bit floats can only reach between -16777215...+16777215 (25 bits) before it
starts losing whole-number accuracy. Some compiler optimizations may break
trying to multiply a float by 2147483647.0 when the result is given right to a
float parameter, causing it instead to multiply by the nearest representable
float value, 2147483648.0.

1 files changed, 10 insertions, 7 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index 424b12ac..1288f7b2 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -912,24 +912,27 @@ ALvoid CalcSourceParams(ALsource *ALSource, const ALCcontext *ALContext)
 }
 
 
-static __inline ALfloat aluF2F(ALfloat val)
-{ return val; }
-static __inline ALint aluF2I(ALfloat val)
+static __inline ALint aluF2I25(ALfloat val)
 {
     /* Clamp the value between -1 and +1. This handles that with only a single branch. */
     if(fabsf(val) > 1.0f)
         val = (ALfloat)((0.0f < val) - (val < 0.0f));
-    /* Convert to a signed integer, between -2147483647 and +2147483647. */
-    return fastf2i((ALfloat)(val*2147483647.0));
+    /* Convert to a signed integer, between -16777215 and +16777215. */
+    return fastf2i(val*16777215.0f);
 }
+
+static __inline ALfloat aluF2F(ALfloat val)
+{ return val; }
+static __inline ALint aluF2I(ALfloat val)
+{ return aluF2I25(val)<<7; }
 static __inline ALuint aluF2UI(ALfloat val)
 { return aluF2I(val)+2147483648u; }
 static __inline ALshort aluF2S(ALfloat val)
-{ return aluF2I(val)>>16; }
+{ return aluF2I25(val)>>9; }
 static __inline ALushort aluF2US(ALfloat val)
 { return aluF2S(val)+32768; }
 static __inline ALbyte aluF2B(ALfloat val)
-{ return aluF2I(val)>>24; }
+{ return aluF2I25(val)>>17; }
 static __inline ALubyte aluF2UB(ALfloat val)
 { return aluF2B(val)+128; }