From bab3b4a75886acd040e81730d9d3dfb31d4f0d48 Mon Sep 17 00:00:00 2001 From: Benjamin Bellec Date: Thu, 2 Jun 2011 08:31:16 -0600 Subject: [PATCH] mesa: faster logbase2 With minor clean-ups by Brian Paul. Signed-off-by: Brian Paul --- src/mesa/main/teximage.c | 35 +++++++++++------------------------ 1 file changed, 11 insertions(+), 24 deletions(-) diff --git a/src/mesa/main/teximage.c b/src/mesa/main/teximage.c index 4ea9a483c92..3e429110ae9 100644 --- a/src/mesa/main/teximage.c +++ b/src/mesa/main/teximage.c @@ -81,31 +81,18 @@ _mesa_free_texmemory(void *m) /* - * Compute floor(log_base_2(n)). - * If n < 0 return -1. + * Returns the floor form of binary logarithm for a 32-bit integer. */ -static int -logbase2( int n ) -{ - GLint i = 1; - GLint log2 = 0; - - if (n < 0) - return -1; - - if (n == 0) - return 0; - - while ( n > i ) { - i *= 2; - log2++; - } - if (i != n) { - return log2 - 1; - } - else { - return log2; - } +static GLuint +logbase2(GLuint n) +{ + GLuint 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; } -- 2.30.2