Additional memory handler features.

[Marc Glisse]

On Sun, 4 Jan 2015, Victor Shoup wrote:

> But I see mention of itching and scratching: could somebody
> describe what that is or provide a link? Sorry for my ignorance.
> ....and sorry for the length of this post....

The general idea is to push all operations that may fail or otherwise
require customization to user code. There would be a function
mpn_mul_itch that would tell you how much temporary (scratch) space
mpn_mul may need, and mpn_mul would take as argument a pointer to a
buffer of at least this size. Allocation is the user's responsibility. 
There should already be a few functions or macros with "itch" in their 
name.

> [FULL DISCLOSURE: my own, somewhat narrow and selfish goal
> is to see GMP's mpn-level routines throw exceptions, rather
> than abort, with no interface changes.  This is what would work
> best for my own NTL library]

mpn functions have few reasons to abort. Except for allocation failure,
as long as you checked the operands before passing them to GMP...

> [And yet another issue: my understanding is that some OS's actually
> have rather weird ways of dealing with out-of-memory errors:
> malloc always succeeds and returns a non-null pointer, but
> indirecting through that pointer may abort the program.
> In such a setting, all of this memory-related error handling
> stuff is pointless]

Yes. Memory overcommit can often be disabled or mitigated in various
ways, but it does complicate things (get a better OS ;-)

-- 
Marc Glisse