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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Not good for Ada endorsement
Date: Fri, 9 Jul 2021 11:21:02 +0200
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On 7/9/21 11:16 AM, Jeffrey R. Carter wrote:
> On 7/9/21 10:33 AM, Egil H H wrote:
>>
>> On my computer, at least, GNAT is not happy about incrementing Number by 2
>> in the inner loop. I get a bit better performance by modifying the check to
>>
>>        if Number mod 2 /= 0 and then Sieve.Bits(Index_Type(Number)) then
>>
>> and then incrementing Number by 1.
> 
> Since both operands are positive, mod and rem give the same results, and rem is 
> usually a bit faster. It's normally not an issue, but in this case it's done 
> billions of times, so it might make a difference.

Note also that short-circuit forms (and then) require disabling processor-level 
optimizations and may have a negative effect on execution time when used 
unnecessarily.

-- 
Jeff Carter
"Oh Lord, bless this thy hand grenade, that with it thou
mayst blow thine enemies to tiny bits, in thy mercy."
Monty Python and the Holy Grail
24