The patch titled
x86: optimize hweight32()
has been added to the -mm tree. Its filename is
x86-optimize-hweight32.patch
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------------------------------------------------------
Subject: x86: optimize hweight32()
From: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Optimize hweight32 by using the same technique in hweight64. The proof of
this technique can be found in the commit log for
f9b4192923fa6e38331e88214b1fe5fc21583fcc ("bitops: hweight() speedup").
The userspace benchmark on x86_32 showed 20% speedup with bitmap_weight()
which uses hweight32 to count bits for each unsigned long on 32bit
architectures.
int main(void)
{
#define SZ (1024 * 1024 * 512)
static DECLARE_BITMAP(bitmap, SZ) = {
[0 ... 100] = 1,
};
return bitmap_weight(bitmap, SZ);
}
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/hweight.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN lib/hweight.c~x86-optimize-hweight32 lib/hweight.c
--- a/lib/hweight.c~x86-optimize-hweight32
+++ a/lib/hweight.c
@@ -11,11 +11,18 @@
unsigned int hweight32(unsigned int w)
{
+#ifdef ARCH_HAS_FAST_MULTIPLIER
+ w -= (w >> 1) & 0x55555555;
+ w = (w & 0x33333333) + ((w >> 2) & 0x33333333);
+ w = (w + (w >> 4)) & 0x0f0f0f0f;
+ return (w * 0x01010101) >> 24;
+#else
unsigned int res = w - ((w >> 1) & 0x55555555);
res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
res = (res + (res >> 4)) & 0x0F0F0F0F;
res = res + (res >> 8);
return (res + (res >> 16)) & 0x000000FF;
+#endif
}
EXPORT_SYMBOL(hweight32);
_
Patches currently in -mm which might be from akinobu.mita@xxxxxxxxx are
linux-next.patch
x86-optimize-hweight32.patch
ipath-use-bitmap_weight.patch
ntfs-use-bitmap_weight.patch
hpfs-use-hweight32.patch
hpfs-use-bitmap_weight.patch
qnx4-use-hweight8.patch
bitmap-introduce-bitmap_set-bitmap_clear-bitmap_find_next_zero_area.patch
iommu-helper-use-bitmap-library.patch
isp1362-hcd-use-bitmap_find_next_zero_area.patch
mlx4-use-bitmap_find_next_zero_area.patch
sparc-use-bitmap_find_next_zero_area.patch
ia64-use-bitmap_find_next_zero_area.patch
genalloc-use-bitmap_find_next_zero_area.patch
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