From: Brian Paul <brianp@vmware.com>
Date: Thu, 2 Jun 2011 14:43:07 +0000 (-0600)
Subject: util: faster logbase2
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=f62e1f41b4d6047e72222aebbb0b55a508269b0c;p=mesa.git

util: faster logbase2
---

diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
index 2ecade5f7e4..65a99fcb394 100644
--- 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;
 }