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Date: Tue, 24 Jan 2012 09:39:53 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC][PATCH] signrom: Speed up checksum calculation
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Stefan Weil <weil@mail.berlios.de>, Anthony Liguori <aliguori@us.ibm.com>, Christoph Egger <Christoph.Egger@amd.com>, qemu-devel <qemu-devel@nongnu.org>, Alexander Graf <agraf@suse.de>

On 01/23/2012 07:38 PM, Jan Kiszka wrote:
>   nums=`od -A n -t u1 -v -N $size "$1"`
> -for i in ${nums}; do
> -    # add each byte's value to sum
> -    sum=`expr \( $sum + $i \) % 256`
> -done
> -
> -sum=$(( (256 - $sum) % 256 ))

We have a bashism here, so why not do

   sum=$(( ($sum + $i) % 256 ))

and do the same with a one-line patch (two line if you change the header 
to #!/bin/bash)?  It should be just as fast as awk.

Paolo