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math64: Add mul_u64_u32_shr()

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Introduce mul_u64_u32_shr() as proposed by Andy a while back; it
allows using 64x64->128 muls on 64bit archs and recent GCC
which defines __SIZEOF_INT128__ and __int128.

(This new method will be used by the scheduler.)

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: fweisbec@gmail.com
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-hxjoeuzmrcaumR0uZwjpe2pv@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2013-11-18 18:27:06 +01:00 • committed by Ingo Molnar
parent ba1f14fbe7
commit be5e610c0f
3 changed files with 37 additions and 0 deletions
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30
include/linux/math64.h
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@ -133,4 +133,34 @@ __iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
return ret;
}
#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
#ifndef mul_u64_u32_shr
static inline u64 mul_u64_u32_shr(u64 a, u32 mul, unsigned int shift)
{
return (u64)(((unsigned __int128)a * mul) >> shift);
}
#endif /* mul_u64_u32_shr */
#else
#ifndef mul_u64_u32_shr
static inline u64 mul_u64_u32_shr(u64 a, u32 mul, unsigned int shift)
{
u32 ah, al;
u64 ret;
al = a;
ah = a >> 32;
ret = ((u64)al * mul) >> shift;
if (ah)
ret += ((u64)ah * mul) << (32 - shift);
return ret;
}
#endif /* mul_u64_u32_shr */
#endif
#endif /* _LINUX_MATH64_H */