linux-kernel - Re: [PATCH 1/2] bitreversal program

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Date:	Wed, 21 May 2008 10:54:15 +0200 (CEST)
From:	Soumyadip Das Mahapatra <kernelhacker@...ualserver.org>
To:	Benoit Boissinot <bboissin@...il.com>
cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] bitreversal program



On Tue, 20 May 2008, Benoit Boissinot wrote:

> A quick benchmarking (that you should have done at least one your
> computer gives for 100000000 iterations):
> old:
> real	0m1.631s
> user	0m1.628s
> sys	0m0.004s
>
> new:
> real	0m5.553s
> user	0m5.540s
> sys	0m0.004s
>
> So I guess there's no need to discuss this further.

Sorry to disturb you again. But i tested my code against Akinobu's one
and the test result shows my code takes less cpu time than that of
Akinobu's.
Here is the code i used to determine performance
--
#include<stdio.h>
#include<time.h>

int main()
{
 	int i = 100000000;
 	printf("%ld\n", (long)clock());
 	for(; i>0; i--) {
 		bitrev32(0x00face32);
 	}
 	printf("%ld", (long)clock());
}
--
OUTPUT:
[using Akinobu's bitrev32()]
0
6010000

[using my bitrev32()]
0
3990000

And using bitrev8() instead of bitrev32() the result gives the output
like this:
[using Akinobu's bitrev8()]
0
770000

[using my bitrev8()]
0
2360000

My processor is 1.4 GHz one.
I am not forcing you to review my code( or i've no expectation of
inclusion of it ) but its just a curiousity: what is truth behind
the output.

Regards,
Soumya

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