Re: [PATCH 01/10] crc-itu-t: add bit-reversed calculation

Andrew Morton
2009-06-04T00:05:32Z

On Mon, 1 Jun 2009 18:54:42 +0400
Dmitry Eremin-Solenikov <dbaryshkov@gmail.com> wrote:

> From: Darren Salt <linux@youmustbejoking.demon.co.uk>
>
> ..
>
> static inline u16 crc_itu_t_byte(u16 crc, const u8 data)
> {
> return (crc << 8) ^ crc_itu_t_table[((crc >> 8) ^ data) & 0xff];
> }
>
> +static inline u16 crc_itu_t_bitreversed_byte(u16 crc, const u8 data)
> +{
> + return (crc << 8) ^ crc_itu_t_table[((crc >> 8) ^ bitrev8(data)) & 0xff];
> +}

I suspect that inlining these was a mistake, but one which we make often.

> #endif /* CRC_ITU_T_H */
>
> diff --git a/lib/crc-itu-t.c b/lib/crc-itu-t.c
> index a63472b..5562fdd 100644
> --- a/lib/crc-itu-t.c
> +++ b/lib/crc-itu-t.c
> @@ -64,6 +64,24 @@ u16 crc_itu_t(u16 crc, const u8 *buffer, size_t len)
> }
> EXPORT_SYMBOL(crc_itu_t);
>
> +/**
> + * crc_itu_t_bitreversed - Compute the CRC-ITU-T for the data buffer;
> + * the buffer content is assumed to be bit-reversed

kerneldoc doesn't support the breaking of this information across
multiple lines. It'll need to be done as a single 120-column line.

> + * @crc: previous CRC value
> + * @buffer: data pointer
> + * @len: number of bytes in the buffer
> + *
> + * Returns the updated CRC value
> + */
> +u16 crc_itu_t_bitreversed(u16 crc, const u8 *buffer, size_t len)
> +{
> + while (len--)
> + crc = crc_itu_t_bitreversed_byte(crc, *buffer++);
> + return crc;
> +}
> +EXPORT_SYMBOL(crc_itu_t_bitreversed);