Messages in this thread | | | Date | Wed, 11 May 2016 11:31:39 +0200 | From | Peter Zijlstra <> | Subject | Re: [patch V4 09/31] bitops: Add x86-specific parity functions |
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On Wed, May 11, 2016 at 05:16:38PM +0800, zengzhaoxiu@163.com wrote:
> +static inline unsigned int __arch_parity4(unsigned int w) > +{ > + unsigned int res = 0; > + > + asm("test $0xf, %1; setpo %b0" > + : "+q" (res) > + : "r" (w) > + : "cc"); > + > + return res; > +} > + > +static inline unsigned int __arch_parity8(unsigned int w) > +{ > + unsigned int res = 0; > + > + asm("test %1, %1; setpo %b0" > + : "+q" (res) > + : "r" (w) > + : "cc"); > + > + return res; > +} > + > +static inline unsigned int __arch_parity16(unsigned int w) > +{ > + unsigned int res = 0; > + > + asm("xor %h1, %b1; setpo %b0" > + : "+q" (res), "+q" (w) > + : : "cc"); > + > + return res; > +}
Please use the GEN_*_RMWcc() stuff to avoid the setpo where possible.
> + > +#ifdef CONFIG_64BIT > +/* popcnt %eax, %eax -- redundant REX prefix for alignment */ > +#define POPCNT32 ".byte 0xf3,0x40,0x0f,0xb8,0xc0" > +/* popcnt %rax, %rax */ > +#define POPCNT64 ".byte 0xf3,0x48,0x0f,0xb8,0xc0" > +#else > +/* popcnt %eax, %eax */ > +#define POPCNT32 ".byte 0xf3,0x0f,0xb8,0xc0" > +#endif
Yuck, please don't duplicate stuff like this.
> + > +static __always_inline unsigned int __arch_parity32(unsigned int w) > +{ > + unsigned int res; > + unsigned int tmp; > + > + asm(ALTERNATIVE( > + " mov %%eax, %1 \n" > + " shr $16, %%eax \n" > + " xor %1, %%eax \n" > + " xor %%ah, %%al \n" > + " mov $0, %%eax \n" > + " setpo %%al \n", > + POPCNT32 " \n" > + " and $1, %%eax \n", > + X86_FEATURE_POPCNT) > + : "=a" (res), "=&r" (tmp) > + : "a" (w) > + : "cc"); > + > + return res; > +}
How many bytes does that end up being? Should we make it a call?
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