bits: make fallback fls work for negative values

diff --git a/usual/bits.h b/usual/bits.h
index fd2f3ae27257333e4d75c4bc35c471e3d3aec560..31a7033a69bac68353fda3b7a1a70efa5b598253 100644 (file)
--- a/usual/bits.h
+++ b/usual/bits.h
@@ -78,10 +78,11 @@ static inline uint64_t ror64(uint64_t v, int s) { return rol64(v, 64 - s); }
        return (x == 0) ? 0 : ((8*sizeof(type)) - __builtin_clz ## sfx(x))
 #else
 #define _FLS(sfx, type) \
+       unsigned type u = x; \
        unsigned int bit; \
        if (x == 0) return 0; \
        /* count from smallest bit, assuming small values */ \
-       for (bit = 1; x > 1; bit++) x >>= 1; \
+       for (bit = 1; u > 1; bit++) u >>= 1; \
        return bit
 #endif