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Date: Thu, 16 Sep 2010 13:09:33 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 2/5] Support human unit formats in
	strtobytes, eg. 1.0G
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To: Jes Sorensen <Jes.Sorensen@redhat.com>
Cc: armbru@redhat.com, quintela@redhat.com, Avi Kivity <avi@redhat.com>, qemu-devel@nongnu.org

On 09/16/2010 12:42 PM, Jes Sorensen wrote:
> On 09/16/10 12:40, Avi Kivity wrote:
>>   On 09/15/2010 09:31 PM, Jes Sorensen wrote:
>>> Floating point is just plain wrong.
>>
>> Why?  If command-line processing becomes too slow, you can always buy a
>> math co-processor.
>
> Because it's imprecise anyway

As Avi mentioned, this is only true if you need byte precision beyond 4 
PB.  But most of the time byte precision is not necessary so in practice 
floating-point will be indistinguishable: all exact powers of 10 up to 
10^22 (beyond 64-bits) can be represented correctly by an IEEE double.

There's also strtold, if you're worried about precision...

> Besides, most users will probably hit their shell command line limit
> before hitting the problem with the decimals.

Value is first shifted and then multiplied, so that 6-7 digits may 
already overflow if the unit is terabytes.

Paolo