Eric Lee / smarc-fsl-linux-kernel

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Commit 39d997b514e12d5aff0dca206eb8996b3957927e

Authored by Akinobu Mita
Committed by Ingo Molnar
1 parent 6b7b284958
Exists in master and in 39 other branches 8mp-imx_5.4.70_2.3.0, 8qm-imx_5.4.70_2.3.0, emb_imx_lf-5.15.y, emb_lf-6.1.y, imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, imx_4.1.15_1.0.0_ga, pitx_8mp_lf-5.10.y, rt-smarc-imx_4.1.15_1.0.0_ga, rt_linux_5.15.71, smarc-8m-android-11.0.0_2.0.0, smarc-imx6_4.14.98_2.0.0_ga, smarc-imx6_4.9.88_2.0.0_ga, smarc-imx7_4.14.98_2.0.0_ga, smarc-imx7_4.9.11_1.0.0_ga, smarc-imx7_4.9.88_2.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-imx_4.1.15_1.0.0_ga, smarc-imx_4.9.11_1.0.0_ga, smarc-imx_4.9.51_imx8m_ga, smarc-imx_4.9.88_2.0.0_ga, smarc-m6.0.1_2.1.0-ga, smarc-n7.1.2_2.0.0-ga, smarc-rel_imx_4.1.15_1.2.0_ga, smarc_8m_00d0_imx_4.14.98_2.0.0_ga, smarc_8m_imx_4.14.78_1.0.0_ga, smarc_8m_imx_4.14.98_2.0.0_ga, smarc_8m_imx_4.19.35_1.1.0, smarc_8mm_imx_4.14.78_1.0.0_ga, smarc_8mm_imx_4.14.98_2.0.0_ga, smarc_8mm_imx_4.19.35_1.1.0, smarc_8mm_imx_5.4.24_2.1.0, smarc_8mp_lf-5.10.y, smarc_8mq_imx_5.4.24_2.1.0, smarc_8mq_lf-5.10.y, smarc_imx_lf-5.15.y

x86, core: Optimize hweight32() 

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@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1258603932-4590-1-git-send-email-akinobu.mita@gmail.com>
[ only x86 sets ARCH_HAS_FAST_MULTIPLIER so we do this via the x86 tree]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Showing 1 changed file with 7 additions and 0 deletions Side-by-side Diff

... ... @@ -11,11 +11,18 @@
11 11  
12 12 unsigned int hweight32(unsigned int w)
13 13 {
  14 +#ifdef ARCH_HAS_FAST_MULTIPLIER
  15 + w -= (w >> 1) & 0x55555555;
  16 + w = (w & 0x33333333) + ((w >> 2) & 0x33333333);
  17 + w = (w + (w >> 4)) & 0x0f0f0f0f;
  18 + return (w * 0x01010101) >> 24;
  19 +#else
14 20 unsigned int res = w - ((w >> 1) & 0x55555555);
15 21 res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
16 22 res = (res + (res >> 4)) & 0x0F0F0F0F;
17 23 res = res + (res >> 8);
18 24 return (res + (res >> 16)) & 0x000000FF;
  25 +#endif
19 26 }
20 27 EXPORT_SYMBOL(hweight32);
21 28