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https://github.com/edk2-porting/linux-next.git
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d61931d89b
Add support for the hardware version of the Hamming weight function, popcnt, present in CPUs which advertize it under CPUID, Function 0x0000_0001_ECX[23]. On CPUs which don't support it, we fallback to the default lib/hweight.c sw versions. A synthetic benchmark comparing popcnt with __sw_hweight64 showed almost a 3x speedup on a F10h machine. Signed-off-by: Borislav Petkov <borislav.petkov@amd.com> LKML-Reference: <20100318112015.GC11152@aftab> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
60 lines
1.3 KiB
C
60 lines
1.3 KiB
C
#ifndef _ASM_X86_HWEIGHT_H
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#define _ASM_X86_HWEIGHT_H
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#ifdef CONFIG_64BIT
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/* popcnt %rdi, %rax */
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#define POPCNT ".byte 0xf3,0x48,0x0f,0xb8,0xc7"
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#define REG_IN "D"
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#define REG_OUT "a"
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#else
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/* popcnt %eax, %eax */
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#define POPCNT ".byte 0xf3,0x0f,0xb8,0xc0"
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#define REG_IN "a"
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#define REG_OUT "a"
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#endif
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/*
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* __sw_hweightXX are called from within the alternatives below
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* and callee-clobbered registers need to be taken care of. See
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* ARCH_HWEIGHT_CFLAGS in <arch/x86/Kconfig> for the respective
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* compiler switches.
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*/
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static inline unsigned int __arch_hweight32(unsigned int w)
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{
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unsigned int res = 0;
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asm (ALTERNATIVE("call __sw_hweight32", POPCNT, X86_FEATURE_POPCNT)
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: "="REG_OUT (res)
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: REG_IN (w));
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return res;
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}
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static inline unsigned int __arch_hweight16(unsigned int w)
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{
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return __arch_hweight32(w & 0xffff);
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}
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static inline unsigned int __arch_hweight8(unsigned int w)
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{
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return __arch_hweight32(w & 0xff);
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}
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static inline unsigned long __arch_hweight64(__u64 w)
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{
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unsigned long res = 0;
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#ifdef CONFIG_X86_32
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return __arch_hweight32((u32)w) +
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__arch_hweight32((u32)(w >> 32));
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#else
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asm (ALTERNATIVE("call __sw_hweight64", POPCNT, X86_FEATURE_POPCNT)
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: "="REG_OUT (res)
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: REG_IN (w));
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#endif /* CONFIG_X86_32 */
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return res;
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}
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#endif
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