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Date: Sun, 27 Nov 2016 15:15:41 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: [PATCH] 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 64byte 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).
---
src/malloc/malloc.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index b90636c..ce2e97d 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[64] = {
+ 0, 0, 0, 0,32,33,34,35,36,36,37,37,38,38,39,39,
+ 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];
if (x > 0x1c00) return 63;
- return ((union { float v; uint32_t r; }){(int)x}.r>>21) - 496;
+ return bin_tab[x/128] + 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] + 1;
+ return bin_tab[x/128] + 17;
}
#if 0
--
2.10.2
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