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malloc: cast size down to int in bin_index functions

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even if size_t was 32-bit already, the fact that the value was
unsigned and that gcc is too stupid to figure out it would be positive
as a signed quantity (due to the immediately-prior arithmetic and
conditionals) results in gcc compiling the integer-to-float conversion
as zero extension to 64 bits followed by an "fildll" (64 bit)
instruction rather than a simple "fildl" (32 bit) instruction on x86.
reportedly fildll is very slow on certain p4-class machines; even if
not, the new code is slightly smaller.
This commit is contained in:
Rich Felker 2011-06-12 10:53:42 -04:00
commit 2afebbbcd1
1 changed files with 2 additions and 2 deletions
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4
src/malloc/malloc.c
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@ -120,14 +120,14 @@ static int bin_index(size_t x)
x = x / SIZE_ALIGN - 1;
if (x <= 32) return x;
if (x > 0x1c00) return 63;
return ((union { float v; uint32_t r; }){ x }.r>>21) - 496;
return ((union { float v; uint32_t r; }){(int)x}.r>>21) - 496;
}
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; }){ x }.r+0x1fffff>>21) - 496;
return ((union { float v; uint32_t r; }){(int)x}.r+0x1fffff>>21) - 496;
}
#if 0