Messages in this thread Patch in this message | | | Date | Wed, 28 Aug 2019 18:11:23 +0200 | From | Peter Zijlstra <> | Subject | [PATCH] x86/math64: Provide a sane mul_u64_u32_div() implementation for x86_64 |
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On Wed, Aug 28, 2019 at 05:19:21PM +0200, Peter Zijlstra wrote: > On Mon, Aug 26, 2019 at 07:47:35AM -0700, kan.liang@linux.intel.com wrote:
> > + return mul_u64_u32_div(slots, val, 0xff); > > But also; x86_64 seems to lack a sane implementation of that function, > and it currently compiles into utter crap (it can be 2 instructions).
--- Subject: x86/math64: Provide a sane mul_u64_u32_div() implementation for x86_64 From: Peter Zijlstra <peterz@infradead.org> Date: Wed Aug 28 17:39:46 CEST 2019
On x86_64 we can do a u64 * u64 -> u128 widening multiply followed by a u128 / u64 -> u64 division to implement a sane version of mul_u64_u32_div().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/include/asm/div64.h | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/arch/x86/include/asm/div64.h +++ b/arch/x86/include/asm/div64.h @@ -73,6 +73,19 @@ static inline u64 mul_u32_u32(u32 a, u32 #else # include <asm-generic/div64.h> + +static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 div) +{ + u64 q; + + asm ("mulq %2; divq %3" : "=a" (q) + : "a" (a), "rm" (mul), "rm" (div) + : "rdx"); + + return q; +} +#define mul_u64_u32_div mul_u64_u32_div + #endif /* CONFIG_X86_32 */ #endif /* _ASM_X86_DIV64_H */
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