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

[Ravi Kerur <rkerur@gmail.com>]

On Mon, May 11, 2015 at 3:29 PM, Don Provan <dprovan@bivio.net> wrote:

> I probably shouldn't stick my nose into this, but I can't help myself.
>
> An experienced programmer will tend to ignore the documentation for
> a routine named "blahblah_memcmp" and just assume it functions like
> memcmp. Whether or not there's currently a use case in DPDK is
> completely irrelevant because as soon as there *is* a use case, some
> poor DPDK developer will try to use rte_memcmp for that and may or
> may not have a test case that reveals their mistake.
>

In general I agree with you. However, comparison is a hit(equal) or
miss(unequal) is generally the case in networking. I haven't seen cases
where "less than" or "greater than" has mattered.


>
> The term "compare" suggests checking for larger or smaller.
> If you want to check for equality, use "equal" or "eq" in the name
> and return true if they're equal. But personally, I'd compare unless
> there was a good reason not to. Indeed, I would just implement
> full memcmp functionality and be done with it, even if that meant
> using my fancy new assembly code for the cases I handle and then
> calling memcmp itself for the cases I didn't.
>
> Agreed, I will look into implementing full functionality.


> If a routine that appears to take an arbitrary size doesn't, the name
> should in some manner reflect what sizes it takes. Better would be
> for a routine that only handles specific sizes to be split into versions
> that only take fixed sizes, but I don't know enough about your use
> cases to say whether that makes sense here.
>
>
Users of rte_memcmp will be existing dpdk test and library code.

-don provan
> dprovan@bivio.net
>
> -----Original Message-----
> From: Ravi Kerur [mailto:rkerur@gmail.com]
> Sent: Monday, May 11, 2015 1:47 PM
> To: Ananyev, Konstantin
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] Implement memcmp using AVX/SSE
> instructions.
>
> ...
> Following memcmp semantics is not hard but there are no use-cases for it
> in DPDK currently. Keeping it specific to DPDK usage simplifies code as
> well.
> I can change the name to "rte_compare" and add comments to the function.
> Will it work?
> ...
>
>