Re: [PATCH] Re: Bignum performance

[Po Lu]

Emanuel Berg <incal@dataswamp.org> writes:

> Po Lu wrote:
>
>>>> Under Arm64, general purpose integer registers are 64 bits
>>>> wide. That is also the word size of said machine.
>>>
>>> If they are, the range for fixnums is
>>>
>>> (list (* -1 (expt 2 (1- 64)))
>>>       (1-   (expt 2 (1- 64))) )
>>>
>>> (-9223372036854775808 9223372036854775807)
>>>
>>> Only after that it gets slower :P
>>
>> Lisp systems normally set aside several of the high or low
>> bits of a register as a tag linking a type to the
>> object represented.
>
> But here we are at the CPU architecture level (register
> length), surely Lisp don't meddle with that?
>
> No, I sense that it is, actually. So please explain, then, how
> it works. And in particular, how many bits do we (Elisp and
> CL) actually have for our fixnums?

I don't know about SBCL, but as for Emacs, refer to the definition of
VALBITS in lisp.h (maybe also the right files among m/*.h and s/*.h, but
I have no idea where they've disappeared to.)