diff options
| -rw-r--r-- | common/math.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/common/math.h b/common/math.h index e1af433f7c..9542cb601a 100644 --- a/common/math.h +++ b/common/math.h @@ -50,6 +50,20 @@ struct Complex { float re, im; }; +#ifdef __GNUC__ +inline int intLog2(uint32 v) { + // This is a slightly optimized implementation of log2 for natural numbers + // targeting gcc. It also saves some binary size over our fallback + // implementation, since it does not need any table. + if (v == 0) + return -1; + else + // This is really "sizeof(unsigned int) * CHAR_BIT - 1" but using 8 + // instead of CHAR_BIT is sane enough and it saves us from including + // limits.h + return (sizeof(unsigned int) * 8 - 1) - __builtin_clz(v); +} +#else // See http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup static const char LogTable256[256] = { #define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n @@ -66,6 +80,7 @@ inline int intLog2(uint32 v) { else return (t = v >> 8) ? 8 + LogTable256[t] : LogTable256[v]; } +#endif inline float rad2deg(float rad) { return rad * 180.0 / M_PI; |