Some asm() correction.

[fjl] / dehuff.h

diff --git a/dehuff.h b/dehuff.h
index 9243e101530018b346e80e2db8b64b96dee1db61..2669034554c25fb16362ace9879f5fa280be9592 100644 (file)
--- a/dehuff.h
+++ b/dehuff.h
@@ -81,13 +81,24 @@ static const int bit_thresholds[16] = {
        0, 1 << 0, 1 << 1, 1 << 2, 1 << 3, 1 << 4, 1 << 5, 1 << 6, 1 << 7, 1 << 8, 1 << 9, 1 << 10, 1 << 11, 1 << 12, 1 << 13, 1 << 14
 };
 
-static inline unsigned extend(int val, int bits)
+static inline unsigned extend(int val, unsigned bits)
 {
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+       // GCC should ideally be able to figure out that the conditional move is better, but
+       // it doesn't for various reasons, and this is pretty important for speed, so we hardcode.
+       asm("cmp %1, %0 ; cmovl %2, %0"
+               : "+r" (val)
+               : "g" (bit_thresholds[bits]),
+                 "r" (val + (-1 << bits) + 1)
+               : "cc");
+       return val;
+#else
        if (val < bit_thresholds[bits]) {
                return val + (-1 << bits) + 1;
        } else {
                return val;
        }
+#endif
 }
 
 #endif /* !defined(_DEHUFF_H) */