Le Chaud Lapin wrote:
> On Apr 28, 9:34 pm, Mathias Gaunard <loufo...@[EMAIL PROTECTED]
> wrote:
>> On 27 avr, 15:29, Le Chaud Lapin <jaibudu...@[EMAIL PROTECTED]
> wrote:
>>
>>> I tried:
>>> #define MULTIPLY(A, B, lower_word, upper_word)\
>>> {\
>>> _asm mov eax, A;\
>>> _asm mul B;\
>>> _asm mov upper_word, edx;\
>>> _asm mov lower_word, eax;\
>>> }
>> What's the point of using macros? Use functions
>
> Functions would make things worse (slower). They would add prolog and
> epilog code. At the very least, a CALL/RET pair would have to be
> executed using straight C++ code. Trickery to get rid of the prolog/
> epilog code would not help, nor would making the function inline,
> because the problem is the C++ code itself. The part that does the
> mathematical operations is too slow, and it is logically impossible
> for the programmer to do anything about it, in C++.
>
> For example, in a Big Integer class, on say, a 32-bit machine, for
> optimal speed, one would necessarily have to multiply two 32-bit
> numbers, A * B to yield a 64-bit result. It is impossible to achieve
> the efficiency of a hardware-based 32-bit * 32-bit multipication using
> ****table C++ code.
>
> Big integers are used as the basis of the RSA and DSA ciphers, and
> asymmetric crytopsystems in general, for example, and such asymmetric
> ciphers are used for packet signing in communications. Because
> asymmetric crypto is often the bottleneck in secure communications,
> their execution speed is paramount. It would be hard to ignore a 3x or
> 4x increase in speed by switching to assembly versus C++.
>
> If the reasons for adding __asm to C++ were listed in order of
> im****tance, I'd say speed up of critical operations would be in the
> top 10. :)
>
Agreed (a pity that C++'s asm keyword is so poorly sup****ted) but that
has nothing to do with functions versus macors. The C++ way is to use
inline functions unless your implementation ignores the inline.
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