-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 06/10/2010 01:50 PM, DE wrote:
[...] I assume you wanted to use stack-based memory for speed, but due to the above, it would likely be slower than the equivalent heap-based integer. Especially with a good caching allocator. [...]
yes you are right i can see the rationale behind this now i guess the cost of allocation compared to cost of operations is negligible so in fact stack version will not gain much and it seems to me that i recalled the discussion about it
If you're doing anything more than simple addition and subtraction, it probably will be.
anyway i think that fixed integer is a valuable part of the lib one more question arises is that many algorithms that use built-in integer modular arithmetic can be generalized to larger ints (PRNG, hash etc.)
I'm not sure I understand what you're saying there.
but as i understood from the docs fixed_integer does not exercise modular arithmetic like built-in types do
The library's fixed-size integers act like unsigned ints, as far as modular arithmetic goes. Except, of course, that they're signed as well. That's why I took pains to describe their behavior thoroughly, it's not entirely obvious from knowledge of the built-in types.
at the same time there already is modular arithmetic implementation in the lib it confuses me what was your intention?
To provide a fixed-integer implementation, primarily because you requested it. :-) The fixed-integer stuff that the library provides is somewhat more flexible than just relying on the modular behavior of the built-in types though, because you can specify a number of bits that isn't necessarily an even multiple of a built-in type's size. For example, it allows 56-bit, 112-bit, and 168-bit integers (the key sizes for Triple-DES) on a 32- or 64-bit machine, even though none of those sizes are a multiple of 32 or 64. That said, the version I'm finishing up now *does* take advantage of the built-in types' behavior when the number of bits is an even multiple of the underlying type's size, to squeeze a little extra performance out of it by eliminating unneeded instructions at compile-time. (Since some people will complain about my example: yes, it's contrived. You don't need a large-integer library for Triple-DES, and you could use a larger value and simply cut it down to the required bits. I was just trying to show one place where it might be useful to calculate something with an unusual number of bits.) - -- Chad Nelson Oak Circle Software, Inc. * * * -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkwRNyMACgkQp9x9jeZ9/wSdwwCdGbskHqLFeoZ9dpW2NeIB5jLi ZzMAoMWGbfhiQtcberJIujrVH9JRbEaI =EDY1 -----END PGP SIGNATURE-----