Add a faster double-to-int converter for x87 builds

1 files changed, 25 insertions, 1 deletions

diff --git a/Alc/effects/pshifter.c b/Alc/effects/pshifter.c
index bf36f5eb..7411f705 100644
--- a/Alc/effects/pshifter.c
+++ b/Alc/effects/pshifter.c
@@ -108,8 +108,32 @@ static alonce_flag HannInitOnce = AL_ONCE_FLAG_INIT;
 
 static inline ALint double2int(ALdouble d)
 {
-    /* TODO: Make a more efficient version for x87. */
+#if ((defined(__GNUC__) || defined(__clang__)) && (defined(__i386__) || defined(__x86_64__)) && \
+     !defined(__SSE2_MATH__)) || (defined(_MSC_VER) && defined(_M_IX86_FP) && _M_IX86_FP < 2)
+    ALint sign, shift;
+    ALint64 mant;
+    union {
+        ALdouble d;
+        ALint64 i64;
+    } conv;
+
+    conv.d = d;
+    sign = (conv.i64>>63) | 1;
+    shift = ((conv.i64>>52)&0x7ff) - (1023+52);
+
+    /* Over/underflow */
+    if(UNLIKELY(shift >= 63 || shift < -52))
+        return 0;
+
+    mant = (conv.i64&U64(0xfffffffffffff)) | U64(0x10000000000000);
+    if(LIKELY(shift < 0))
+        return (ALint)(mant >> -shift) * sign;
+    return (ALint)(mant << shift) * sign;
+
+#else
+
     return (ALint)d;
+#endif
 }