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Re: [PATCH] x86-64: Add memcmp/wmemcmp optimized with AVX2
On Thu, Jun 1, 2017 at 2:00 PM, Florian Weimer <firstname.lastname@example.org> wrote:
> On 06/01/2017 10:57 PM, H.J. Lu wrote:
>> I don't think it works with memcmp since return value depends on
>> the first bytes which differs. Say
>> ABCDE turns into EDCBDCBA
>> If all bytes differs, we should only compare A, not EDCBDCBA.
> That's what the bswapq is for, it reverses the order of bytes.
bswapq doesn't help since cmpq compares 8 bytes but only
the last byte matters. Comparing the highest byte give you the
wrong result, like