From 0fc163408e6b9521d545daba19f70631011d5752 Mon Sep 17 00:00:00 2001 From: Kenneth Graunke Date: Tue, 11 Sep 2012 22:14:58 -0700 Subject: [PATCH] mesa: Add a _mesa_fls() function to find the last bit set in a word. ffs() finds the least significant bit set; _mesa_fls() finds the /most/ significant bit. v2: Make it an inline function in imports.h, per Brian's suggestion. Signed-off-by: Kenneth Graunke Reviewed-by: Brian Paul Reviewed-by: Matt Turner --- src/mesa/main/imports.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/src/mesa/main/imports.h b/src/mesa/main/imports.h index abf216c99ac..81da5104717 100644 --- a/src/mesa/main/imports.h +++ b/src/mesa/main/imports.h @@ -520,6 +520,28 @@ extern unsigned int _mesa_bitcount_64(uint64_t n); #endif +/** + * Find the last (most significant) bit set in a word. + * + * Essentially ffs() in the reverse direction. + */ +static inline unsigned int +_mesa_fls(unsigned int n) +{ +#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 304) + return n == 0 ? 0 : 32 - __builtin_clz(n); +#else + unsigned int v = 1; + + if (n == 0) + return 0; + + while (n >>= 1) + v++; + + return v; +#endif +} extern GLhalfARB _mesa_float_to_half(float f); -- 2.30.2