util: faster logbase2

diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
index 2ecade5..65a99fc 100644 (file)
--- a/src/gallium/auxiliary/util/u_math.h
+++ b/src/gallium/auxiliary/util/u_math.h
@@ -477,10 +477,13 @@ float_to_byte_tex(float f)
 static INLINE unsigned
 util_logbase2(unsigned n)
 {
-   unsigned log2 = 0;
-   while (n >>= 1)
-      ++log2;
-   return log2;
+   unsigned pos = 0;
+   if (n >= 1<<16) { n >>= 16; pos += 16; }
+   if (n >= 1<< 8) { n >>=  8; pos +=  8; }
+   if (n >= 1<< 4) { n >>=  4; pos +=  4; }
+   if (n >= 1<< 2) { n >>=  2; pos +=  2; }
+   if (n >= 1<< 1) {           pos +=  1; }
+   return pos;
 }