On Tue, 25 Oct 2011 09:43:48 +0200, Piotr Szturmaj <bncr...@jadamspam.pl>
wrote:
Martin Nowak wrote:
I have to say though that I like the current struct based interface
much better.
struct Hash
{
// enhanced by some compile time traits
enum hashLength = 16;
enum blockLength = 0;
The reason why hash and block length are runtime variables is that some
hash functions are parametrized with variables of great amplitude, for
example CubeHash may have any number of rounds, and any size of block
and hash output.
// three interface functions
void start();
void update(const(ubyte)[] data);
void finish(ref ubyte[hashLength] digest);
}
There, it is:
reset();
put();
finish();
Reset does two different things depending on the internal state. Not so
good.
The put() function makes hash implementation an OutputRange.
You wouldn't need the save, restore functions.
They're not needed. They only serve as speed optimization when hashing
many messages which have the same beginning block. This is used in HMAC,
which is:
HMAC(func, key, message) = func(key ^ opad, func(key ^ ipad, message));
when func supports saving the IV, the first parts are precomputed, when
not HMAC resorts to full hashing. This optimization is also mentioned in
HMAC spec.
If hash contexts were value type you could simply do.
auto saved = hash_ctx;
Or alternatively one could add a 'save()' function to an isSaveableHash(H)
concept.
Some unnecessary allocations could go away.
Most important instances would have less mutable state.
Could you specify which ones, please?
Basically every 'new' in std.hash.crypto.base but especially the ones in
hash(T) and hashToHex(T).
You could probably parameterize a Merkle Damgård base with free
functions for the transformation.
What would be the difference from current class parametrization?
Just wanted to point out a specific alternative if code reuse is of a
concern.
If not using classes you need a way to inject the transformation which
could
be done like.
alias MerkleDamgard!(uint, 5, 80, 16, 20, sha1Transform) SHA1;
A dynamic interface can be obtaines by templated instances similar to
what std.range does.
Could you elaborate? I don't know exactly what do you mean. Function
templates?
http://www.digitalmars.com/d/2.0/phobos/std_range.html#InputRange
DynamicAllocatorTemplate at
https://github.com/dsimcha/TempAlloc/blob/master/std/allocators/allocator.d
These are to support cases where you either want a stable ABI or
have a template firewall for scalability issues (e.g. could be sensible
for the HMAC implementation although not really necessary).
Thanks a lot!
