Is there a good lib out there to handle large integer of know size ?

[Era Scarecrow via Digitalmars-d]

On Sunday, 11 June 2017 at 21:52:40 UTC, Era Scarecrow wrote:
>  Doing a 10240bit int I ran though 1,000 factorials in 6 
> seconds (this includes printing the values out). I got to about 
> 400 in 16 minutes using the generic code.

  Got the compatible/generic code to run far faster, about 7 times 
slower vs the assembly language version!

  Probably the last of those optimizations I'll be making, don't 
think i can squeeze too much more out of it.