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

zhaoxiu.zeng
2016-03-27T13:38:59Z

On 2016/3/27 20:44, Sam Ravnborg wrote:
> Hi Zeng.
>
> Looking through the arch specific implementations of __arch_parity().
> Some architectures uses #defines, other uses inline static functions.
>
> Any particular reason that you select one approach over the other
> in the different cases?
>
> ia64:
> +#define __arch_parity32(x) ((unsigned int) __arch_parity64((x) & 0xfffffffful))
> +#define __arch_parity16(x) ((unsigned int) __arch_parity64((x) & 0xfffful))
> +#define __arch_parity8(x) ((unsigned int) __arch_parity64((x) & 0xfful))
> +#define __arch_parity4(x) ((unsigned int) __arch_parity64((x) & 0xful))
>
> tile:
> +static inline unsigned int __arch_parity32(unsigned int w)
> +{
> + return __builtin_popcount(w) & 1;
> +}
> +
> +static inline unsigned int __arch_parity16(unsigned int w)
> +{
> + return __arch_parity32(w & 0xffff);
> +}
> +
> +static inline unsigned int __arch_parity8(unsigned int w)
> +{
> + return __arch_parity32(w & 0xff);
> +}
> +
> +static inline unsigned int __arch_parity4(unsigned int w)
> +{
> + return __arch_parity32(w & 0xf);
> +}
>

No particular reason, just like the architecture's __arch_hweightN.

> Just two examples.
>
> Adding the parity helpers seems like veny nice simplifications.
>
> A few comments to some of those I looked at.
> (I am not subscribed to lkml, so you get it as comments here)
>

I think the conversion is simple and readable.

> [PATCH 21/31] mtd: use parity16 in ssfdc.c
> The original code semes to check that the parity equals the
> value of first bit in the address.
> This seems lost after the conversion.
>

The original get_parity return 1 if the number is even, so
if block_address is valid, "block_address & 0x7ff" must be odd.

> [PATCH 20/31] scsi: use parity32 in isci/phy.c
> + if (parity32(phy_cap.all))
> phy_cap.parity = 1;
> Could be written like this - simpler IMO:
> phy_cap.parity = parity32(phy_cap.all);
>
>
> Sam
>
Yes. Thanks!