On Tue, Sep 22, 2015 at 04:34:36PM +0200, Christophe Leroy wrote:
> +/*
> + * computes the checksum of a memory block at buff, length len,
> + * and adds in "sum" (32-bit)
> + *
> + * returns a 32-bit number suitable for feeding into itself
> + * or csum_tcpudp_magic
> + *
> + * this function must be called with even lengths, except
> + * for the last fragment, which may be odd
> + *
> + * it's best to have buff aligned on a 32-bit boundary
> + */
> +__wsum __csum_partial(const void *buff, int len, __wsum sum);
> +
> +static inline __wsum csum_partial(const void *buff, int len, __wsum sum)
> +{
> + if (__builtin_constant_p(len) && len == 0)
> + return sum;
> +
> + if (__builtin_constant_p(len) && len <= 16 && (len & 1) == 0) {
> + __wsum sum1;
> +
> + if (len == 2)
> + sum1 = (__force u32)*(u16 *)buff;
> + if (len >= 4)
> + sum1 = *(u32 *)buff;
> + if (len == 6)
> + sum1 = csum_add(sum1, (__force u32)*(u16 *)(buff + 4));
> + if (len >= 8)
> + sum1 = csum_add(sum1, *(u32 *)(buff + 4));
> + if (len == 10)
> + sum1 = csum_add(sum1, (__force u32)*(u16 *)(buff + 8));
> + if (len >= 12)
> + sum1 = csum_add(sum1, *(u32 *)(buff + 8));
> + if (len == 14)
> + sum1 = csum_add(sum1, (__force u32)*(u16 *)(buff + 12));
> + if (len >= 16)
> + sum1 = csum_add(sum1, *(u32 *)(buff + 12));
> +
> + sum = csum_add(sum1, sum);
Why the final csum_add instead of s/sum1/sum/ and putting csum_add in the
"len == 2" and "len >= 4" cases?
The (__force u32) casts are unnecessary. Or rather, it should be
(__force __wsum) -- on all of them, not just the 16-bit ones.
The pointer casts should be const.
> + } else if (__builtin_constant_p(len) && (len & 3) == 0) {
> + sum = csum_add(ip_fast_csum_nofold(buff, len >> 2), sum);
It may not make a functional difference, but based on the csum_add()
argument names and other csum_add() usage, sum should come first
and the new content second.
-Scott