Re: Assembly Language - Mathematics WITHOUT maths coprocessor

On Sat, 08 Oct 2005 02:18:48 -0400, ¬a\/b <al@xxx> wrote:

i think the division in the book "Handbook of Applied Cryptography"
with the base 2^32 is 100x faster than its binary base form

I don't like the way those cryptography people do math. According to them, you can solve x = a + b with the following code:

	mov eax, [a]
	mov edx, [b]
	or eax, edx
	mov [x], eax

What I think has happened is that they're for some reason against using words like "or" and "xor" and so they use "+" and "*" instead. So when they say divide, god only knows what they're actually talking about.

Anyway, if you're mearly dividing large numerators by 32-bit or smaller denominators, that's actually pretty easy and you can do it with an algorithm using the divide instruction, so that you're doing it 32 bits per interation instead of 1 bit per interation. However, once the denominator exceeds the capabilities of the CPU's divide instruction, I don't know what else to do besides shift and subtract. (Of course that doesn't mean that there isn't an easier way, I frequently find that I don't know everything. Well, at least on occasion.)
.

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