Re: [Fastlibnt-devel] Scalar exact division

[David H. <dmh...@ma...>]

On Apr 26, 2007, at 9:38 PM, William Hart wrote:

> Well, my trick works. But it comes at a cost.
>
> I initially set it up to replace all the sign limbs
> with sign*x (since the sign is always +/-1 or 0, no
> actual multiplication actually needs to be performed).
> The idea is to multiply the signs by the appropriate
> amount so that when the division occurs the signs
> return to what they should be.
>
> Well this works for positive signs, but of course it
> fails for negative signs, since you'd have to be doing
> a signed division, which you are not.

Another possibility --- I think --- is to replace the -1 sign limb  
with -x, and then also decrement the next limb along. (i.e. you would  
have to use mpn_sub_1, to propagate any borrows, which is annoying.)  
Then if you divide by x, I think you get what you want. I'm not sure  
if it will be faster though.

david