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Message-ID: <20161127141541.GZ5749@port70.net> 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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