From 325cbeb29a63e3d71da00baeab864970fe3aa595 Mon Sep 17 00:00:00 2001 From: Brian Date: Sun, 9 Nov 2008 10:15:32 -0700 Subject: util: Fix util_fast_pow/exp2/log2. - Use a lookup table for log2. - Compute (float) (1 << ipart) by tweaking with the exponent directly to avoid integer overflow and float conversion. - Also table negative exponents to avoid float division and branching. - Implement util_fast_exp as function of util_fast_exp2. -------- Cherry-picked from gallium-0.2: 8415d06d90a197e16554dab98d160334fd9f9f93 This fixes some pow() glitches seen in fslight.c, spectex.c, etc. Conflicts: src/gallium/auxiliary/util/u_math.h --- src/gallium/auxiliary/util/u_math.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) (limited to 'src/gallium/auxiliary/util/u_math.c') diff --git a/src/gallium/auxiliary/util/u_math.c b/src/gallium/auxiliary/util/u_math.c index 0729114d6a1..5b3cab4642a 100644 --- a/src/gallium/auxiliary/util/u_math.c +++ b/src/gallium/auxiliary/util/u_math.c @@ -30,7 +30,7 @@ #include "util/u_math.h" - +/** 2^x, for x in [-1.0, 1.0[ */ float pow2_table[POW2_TABLE_SIZE]; @@ -38,9 +38,21 @@ static void init_pow2_table(void) { int i; - for (i = 0; i < POW2_TABLE_SIZE; i++) { - pow2_table[i] = (float) pow(2.0, i / POW2_TABLE_SCALE); - } + for (i = 0; i < POW2_TABLE_SIZE; i++) + pow2_table[i] = (float) pow(2.0, (i - POW2_TABLE_OFFSET) / POW2_TABLE_SCALE); +} + + +/** log2(x), for x in [1.0, 2.0[ */ +float log2_table[LOG2_TABLE_SIZE]; + + +static void +init_log2_table(void) +{ + unsigned i; + for (i = 0; i < LOG2_TABLE_SIZE; i++) + log2_table[i] = (float) log2(1.0 + i * (1.0 / LOG2_TABLE_SIZE)); } @@ -53,6 +65,7 @@ util_init_math(void) static boolean initialized = FALSE; if (!initialized) { init_pow2_table(); + init_log2_table(); initialized = TRUE; } } -- cgit v1.2.3