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Re: sprintf() heap usage
- From: Vasili Galka <vvv444 at gmail dot com>
- To: Eric Blake <eblake at redhat dot com>
- Cc: newlib at sourceware dot org
- Date: Tue, 16 Jul 2013 18:23:34 +0300
- Subject: Re: sprintf() heap usage
- References: <CA+gZxsO8PrqwaTU-xMJ1QrOvz3otf_uVt2ap-wGtdKj7niX7GQ at mail dot gmail dot com> <51E56435 dot 60408 at redhat dot com>
I see. Thank you!
On Tue, Jul 16, 2013 at 6:18 PM, Eric Blake <email@example.com> wrote:
> On 07/16/2013 03:39 AM, Vasili Galka wrote:
>> I've been surprised to discover that using sprintf() leads to
>> requirement of sbrk(). Can anyone please explain me why?
>> For gods sake, the function already has output buffer provided. The
>> lifetime of the function is well defined and it has stack. Why would
>> it require heap!?
> Computation of %g and friends can require allocation in order to safely
> convert a power-of-two floating-point number into a power-of-10 string
> representation (particularly for numbers on the extreme small end, like
> 1e-300). Even if the final representation fits in the buffer passed
> into snprintf, the intermediate conversion steps require more bytes than
> can be safely allocated within a single page of the stack, and as newlib
> cannot assume a large stack size, it is easier to implement the
> conversion process using the heap.
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org