From: Szabolcs Nagy <nsz@port70.net>
Date: Sat, 17 Dec 2016 14:03:24 +0000 (+0100)
Subject: use lookup table for malloc bin index instead of float conversion
X-Git-Tag: v1.1.16~9
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=61ff1af76f4887bb7c555e4d0b8a7eeb73b05086;p=oweals%2Fmusl.git

use lookup table for malloc bin index instead of float conversion

float conversion is slow and big on soft-float targets.

The lookup table increases code size a bit on most hard float targets
(and adds 60byte rodata), performance can be a bit slower because of
position independent data access and cpu internal state dependence
(cache, extra branches), but the overall effect should be minimal
(common, small size allocations should be unaffected).
---

diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index b90636cc..c38c46fe 100644
--- a/src/malloc/malloc.c
+++ b/src/malloc/malloc.c
@@ -111,19 +111,29 @@ static int first_set(uint64_t x)
 #endif
 }
 
+static const unsigned char bin_tab[60] = {
+	            32,33,34,35,36,36,37,37,38,38,39,39,
+	40,40,40,40,41,41,41,41,42,42,42,42,43,43,43,43,
+	44,44,44,44,44,44,44,44,45,45,45,45,45,45,45,45,
+	46,46,46,46,46,46,46,46,47,47,47,47,47,47,47,47,
+};
+
 static int bin_index(size_t x)
 {
 	x = x / SIZE_ALIGN - 1;
 	if (x <= 32) return x;
+	if (x < 512) return bin_tab[x/8-4];
 	if (x > 0x1c00) return 63;
-	return ((union { float v; uint32_t r; }){(int)x}.r>>21) - 496;
+	return bin_tab[x/128-4] + 16;
 }
 
 static int bin_index_up(size_t x)
 {
 	x = x / SIZE_ALIGN - 1;
 	if (x <= 32) return x;
-	return ((union { float v; uint32_t r; }){(int)x}.r+0x1fffff>>21) - 496;
+	x--;
+	if (x < 512) return bin_tab[x/8-4] + 1;
+	return bin_tab[x/128-4] + 17;
 }
 
 #if 0