Re: Proposal: block-based vector allocator

[Andreas Schwab]

Dmitry Antipov <address@hidden> writes:

> On 05/21/2012 05:02 PM, Andreas Schwab wrote:
>
>> It doesn't make much sense to try to find such a trivial but non-std
>> macro in a system header.
>
> Hm, glibc provides some not-so-trivial bits (assuming gcc):
>
> # define roundup(x, y)  (__builtin_constant_p (y) && powerof2 (y)             
> \
>                          ? (((x) + (y) - 1) & ~((y) - 1))                     
> \
>                          : ((((x) + ((y) - 1)) / (y)) * (y)))
>
> It seems to be a very negligible optimization, but why not use it if 
> available?

Since you are always using a constant you can define your roundup macro
accordingly.  But note that the expansion is buggy for some types of
arguments, so one more reason not to use it.

Andreas.

-- 
Andreas Schwab, address@hidden
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."