the need for 64 bits

[Mark Dickinson]

On Dec 28, 6:50 am, Mensanator <mensana... at aol.com> wrote:

> But with a 64-bit processor, that limitation no longer stops me.
>
> i: 11   bits: 10,460,353,205   decimals:  3,148,880,080
> i: 12   bits: 94,143,178,829   decimals: 28,339,920,715
>
> Wow! 94 billion bits! 28 billion decimal digits!
>
> Of course, once one wall falls, you get to go up against the next
> one.
> For generation 13, I get:
>
> gmp: overflow in mpz type
> Abort trap
>
> Hmm, not sure what "overflow" means in this context, but I suspect
> it ran out of memory, I probably should have gotten the MacBook Pro
> with 8 GB of ram. But then, maybe it wouldn't help.

I don't think this was due to running out of memory:  it looks like
gmp uses the 'int' C type to count the number of limbs in an mpz,
which would make the maximum number of bits 2**31 * 64, or around 137
billion, on a typical 64-bit machine.  Maybe there's a configure
option to change this?

For Python longs, the number of limbs is stored as a signed size_t
type, so on a 64-bit machine memory really is the only limitation.

--
Mark