Additional memory handler features.
shoup at cs.nyu.edu
Mon Jan 5 20:38:56 UTC 2015
Thanks. This would more-or-less solve all my problems,
if and when it all gets implemented. I don't find such functions
right now in the GMP manual.
On Jan 4, 2015, at 6:08 PM, Niels Möller wrote:
> Victor Shoup <shoup at cs.nyu.edu> writes:
>> 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 idea is that instead of having gmp allocate temporary storage, it
> should have a function to tell how much temporary storage is needed for
> each operation, and then let the application allocate that anyway it
> please, and pass it as an additional argument. So instead of
> mpn_mul (rp, ap, an, bp, bn);
> one would do something like
> mp_limb_t *scratch = xalloc (sizeof(mp_limb_t) * mpn_mul_itch (an, bn));
> mpn_mul (rp, ap, bn, bp, bn, scratch);
> free (scratch);
> For convenience, higher level functions could allow a NULL scratch
> argument, and allocate temporary storage using registered gmp allocation
> All this applies to mpn functions only.
> There are several motivations for this type of interface:
> 1. For low-level mpn loops, this helps eliminate the frame pointer,
> making one more register available. (Functions using alloca need a
> frame pointer).
> 2. For higher-level functions, it may help reuse temporary storage,
> reducing the total storage need of GMP.
> 3. It should make it possible for applications to allocate temporary
> storage up front. E.g., when a cryptographic application initializes
> a key, it may allocate up front all temporary storage needed for
> operations using that key, so that later operations can never fail
> for memory allocation reasons. Even static allocation may be possible
> in some cases.
> Of course there are also some drawbacks. It makes life more complicated
> for applications, and the implementation of functions like mpn_mul_itch,
> which interact with pretty complex algorithm choice machinery, is going
> to be a bit complex too.
> Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
> Internet email is subject to wholesale government surveillance.
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