Re: [dpdk-dev] [PATCH v2] Implement memcmp using AVX/SSE instructions.

[Matt Laswell <laswell@infiniteio.com>]

On Fri, May 8, 2015 at 4:19 PM, Ravi Kerur <rkerur@gmail.com> wrote:

> This patch replaces memcmp in librte_hash with rte_memcmp which is
> implemented with AVX/SSE instructions.
>
> +static inline int
> +rte_memcmp(const void *_src_1, const void *_src_2, size_t n)
> +{
> +       const uint8_t *src_1 = (const uint8_t *)_src_1;
> +       const uint8_t *src_2 = (const uint8_t *)_src_2;
> +       int ret = 0;
> +
> +       if (n & 0x80)
> +               return rte_cmp128(src_1, src_2);
> +
> +       if (n & 0x40)
> +               return rte_cmp64(src_1, src_2);
> +
> +       if (n & 0x20) {
> +               ret = rte_cmp32(src_1, src_2);
> +               n -= 0x20;
> +               src_1 += 0x20;
> +               src_2 += 0x20;
> +       }
>
>
Pardon me for butting in, but this seems incorrect for the first two cases
listed above, as the function as written will only compare the first 128 or
64 bytes of each source and return the result.  The pattern expressed in
the 32 byte case appears more correct, as it compares the first 32 bytes
and then lets later pieces of the function handle the smaller remaining
bits of the sources. Also, if this function is to handle arbitrarily large
source data, the 128 byte case needs to be in a loop.

What am I missing?

--
Matt Laswell
infinite io, inc.
laswell@infiniteio.com