Re: [PATCH 01/31] bitops: add parity functions

Zeng Zhaoxiu
2016-03-29T02:27:46Z

在 2016年03月28日 14:51, Sam Ravnborg 写道:
>> diff --git a/include/asm-generic/bitops/arch_parity.h b/include/asm-generic/bitops/arch_parity.h
>> new file mode 100644
>> index 0000000..cddc555
>> --- /dev/null
>> +++ b/include/asm-generic/bitops/arch_parity.h
>> @@ -0,0 +1,39 @@
>> +#ifndef _ASM_GENERIC_BITOPS_ARCH_PARITY_H_
>> +#define _ASM_GENERIC_BITOPS_ARCH_PARITY_H_
>> +
>> +#include <asm/types.h>
>> +
>> +/*
>> + * Refrence to 'https://graphics.stanford.edu/~seander/bithacks.html#ParityParallel'.
>> + */
>> +
>> +static inline unsigned int __arch_parity4(unsigned int w)
>> +{
>> + w &= 0xf;
>> + return (0x6996 >> w) & 1;
>> +}
>> +
>> +static inline unsigned int __arch_parity8(unsigned int w)
>> +{
>> + w ^= w >> 4;
>> + return __arch_parity4(w);
>> +}
>> +
>> +static inline unsigned int __arch_parity16(unsigned int w)
>> +{
>> + w ^= w >> 8;
>> + return __arch_parity8(w);
>> +}
>> +
>> +static inline unsigned int __arch_parity32(unsigned int w)
>> +{
>> + w ^= w >> 16;
>> + return __arch_parity16(w);
>> +}
>> +
>> +static inline unsigned int __arch_parity64(__u64 w)
>> +{
>> + return __arch_parity32((unsigned int)(w >> 32) ^ (unsigned int)w);
>> +}
> Defining these as static inlines in asm-generic prevent an architecture
> from selecting between a more optimal asm version or the generic version
> at run-time.
> sparc would benefit from this as only some sparc chips supports popc.
> See how this is done for hweight*
>
> Sam

Thanks. I will try.