[Mesa-dev] [PATCH] util: import sha1 implementation from OpenBSD

[Matt Turner]

On Fri, Jan 13, 2017 at 1:01 PM, Vladislav Egorov <vegorov180 at gmail.com> wrote:
> 2017-01-13 22:43 GMT+03:00 Emil Velikov <emil.l.velikov at gmail.com>:
>>
>> On 13 January 2017 at 19:22, Vladislav Egorov <vegorov180 at gmail.com> wrote:
>> > 13.01.2017 19:51, Emil Velikov пишет:
>> >>
>> >> From: Emil Velikov <emil.velikov at collabora.com>
>> >>
>> >> At the moment we support 5+ different implementations each with varying
>> >> amount of bugs - from thread safely problems [1], to outright broken
>> >> implementation(s) [2]
>> >>
>> >> In order to accommodate these we have 150+ lines of configure script and
>> >> extra two configure toggles. Whist an actual implementation being
>> >> ~200loc and our current compat wrapping ~250.
>> >>
>> >> Let's not forget that different people use different code paths, thus
>> >> effectively makes it harder to test and debug since the default
>> >> implementation is automatically detected.
>> >>
>> >> To minimise all these lovely experiences, import the "100% Public
>> >> Domain" OpenBSD sha1 implementation. Clearly document any changes needed
>> >> to get building correctly, since many/most of those can be upstreamed
>> >> making future syncs easier.
>> >
>> >
>> > It can hurt performance.
>> This is not performance critical path ;-) If that ever changes we can
>> rethink our options.
>>
>> Emil
>
>
> If it's used by shader-cache, it's certainly along the critical path.
> And 7-8 cycles per byte (or more than 10 cycles per byte on Atoms,
> Celerons and low-end AMDs) per byte of shader text is something to be
> considered. In comparison the entire preprocessing stage takes ~15
> cycles per byte -- well, after my optimizations :) I regularly see
> util_hash_crc32() in perf top - because it uses inefficient
> table-based implementation with the same ~8 cycles per byte.

Perhaps we should consider using CRC32C (for which an instruction
exists in SSE 4.2 with a latency of 3 cycles) as the hashing function?

http://stackoverflow.com/questions/2694740/can-one-construct-a-good-hash-function-using-crc32c-as-a-base