linux-kernel - Re: [PATCH v12 5/6] lib: add bitrev8x4()

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Date:   Mon, 5 Jun 2017 10:12:30 -0500
From:   Alan Tull <atull@...nel.org>
To:     Joshua Clayton <stillcompiling@...il.com>
Cc:     Moritz Fischer <moritz.fischer@...us.com>,
        Anatolij Gustschin <agust@...x.de>,
        Bastian Stender <bst@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Russell King <linux@...linux.org.uk>,
        linux-fpga@...r.kernel.org,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v12 5/6] lib: add bitrev8x4()

On Fri, Jun 2, 2017 at 3:30 PM, Joshua Clayton <stillcompiling@...il.com> wrote:
> Add a function to reverse bytes within a 32 bit word.
> Operate on a u32 rather than individual bytes.
>
> Signed-off-by: Joshua Clayton <stillcompiling@...il.com>

Signed-off-by: Alan Tull <atull@...nel.org>

> ---
>  include/linux/bitrev.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
> index fb790b8449c1..b97be27e5a85 100644
> --- a/include/linux/bitrev.h
> +++ b/include/linux/bitrev.h
> @@ -29,6 +29,8 @@ static inline u32 __bitrev32(u32 x)
>
>  #endif /* CONFIG_HAVE_ARCH_BITREVERSE */
>
> +#define __bitrev8x4(x) (__bitrev32(swab32(x)))
> +
>  #define __constant_bitrev32(x) \
>  ({                                     \
>         u32 __x = x;                    \
> @@ -50,6 +52,15 @@ static inline u32 __bitrev32(u32 x)
>         __x;                                                            \
>  })
>
> +#define __constant_bitrev8x4(x) \
> +({                     \
> +       u32 __x = x;    \
> +       __x = ((__x & (u32)0xF0F0F0F0UL) >> 4) | ((__x & (u32)0x0F0F0F0FUL) << 4);      \
> +       __x = ((__x & (u32)0xCCCCCCCCUL) >> 2) | ((__x & (u32)0x33333333UL) << 2);      \
> +       __x = ((__x & (u32)0xAAAAAAAAUL) >> 1) | ((__x & (u32)0x55555555UL) << 1);      \
> +       __x;                                                            \
> +})
> +
>  #define __constant_bitrev8(x)  \
>  ({                                     \
>         u8 __x = x;                     \
> @@ -75,6 +86,14 @@ static inline u32 __bitrev32(u32 x)
>         __bitrev16(__x);                                \
>   })
>
> +#define bitrev8x4(x) \
> +({                     \
> +       u32 __x = x;    \
> +       __builtin_constant_p(__x) ?     \
> +       __constant_bitrev8x4(__x) :                     \
> +       __bitrev8x4(__x);                               \
> + })
> +
>  #define bitrev8(x) \
>  ({                     \
>         u8 __x = x;     \
> --
> 2.11.0
>