Re: sprintf() heap usage

[Federico Terraneo <fede dot tft at hotmail dot it>]

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On 07/16/2013 05:23 PM, Vasili Galka wrote:
> I see. Thank you!
> 
> On Tue, Jul 16, 2013 at 6:18 PM, Eric Blake <eblake@redhat.com>
> wrote:
>> On 07/16/2013 03:39 AM, Vasili Galka wrote:
>>> Hi,
>>> 
>>> 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.

You may want to try siprintf(). It's a newlib-specific function that
doesn't support floating point numbers, but has a reduced code size.
Now, I haven't actually checked that it doesn't use the heap (as I
tend to use malloc also in deeply embedded systems), but it might be
worth a try.

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