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Date: Sun, 15 Aug 2021 18:29:08 +0200
From: "Stefan Kanthak" <stefan.kanthak@...go.de>
To: "Rich Felker" <dalias@...c.org>
Cc: "Szabolcs Nagy" <nsz@...t70.net>,
<musl@...ts.openwall.com>
Subject: Re: [PATCH #2] Properly simplified nextafter()
Rich Felker <dalias@...c.org> wrote:
> On Sun, Aug 15, 2021 at 05:19:05PM +0200, Stefan Kanthak wrote:
>> Szabolcs Nagy <nsz@...t70.net> wrote:
>>
>> > * Stefan Kanthak <stefan.kanthak@...go.de> [2021-08-15 09:04:55 +0200]:
>> >> Szabolcs Nagy <nsz@...t70.net> wrote:
>> >>> you should benchmark, but the second best is to look
>> >>> at the longest dependency chain in the hot path and
>> >>> add up the instruction latencies.
>> >>
>> >> 1 billion calls to nextafter(), with random from, and to either 0 or +INF:
>> >> run 1 against glibc, 8.58 ns/call
>> >> run 2 against musl original, 3.59
>> >> run 3 against musl patched, 0.52
>> >> run 4 the pure floating-point variant from 0.72
>> >> my initial post in this thread,
>> >> run 5 the assembly variant I posted. 0.28 ns/call
>> >
>> > thanks for the numbers. it's not the best measurment
>>
>> IF YOU DON'T LIKE IT, PERFORM YOUR OWN MEASUREMENT!
>
> The burden of performing a meaningful measurement is on the party who
> says there's something that needs to be changed.
I offered you two patches which speed a rather simple function by a
measured factor of 5 and 7 respectively. IF YOU DOUBT THESE NUMBERS,
PROVIDE YOUR OWN!
Stefan
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