Re: [PATCH] Use 128-bit math to accelerate numeric division, when 8 < divisor digits <= 16

On Sun, 22 Jan 2023 at 13:42, Joel Jacobson <joel(at)compiler(dot)org> wrote:
>
> Hi,
>
> On platforms where we support 128bit integers, we could accelerate division
> when the number of digits in the divisor is larger than 8 and less than or
> equal to 16 digits, i.e. when the divisor that fits in a 64-bit integer but would
> not fit in a 32-bit integer.
>

Seems like a reasonable idea, with some pretty decent gains.

Note, however, that for a divisor having fewer than 5 or 6 digits,
it's now significantly slower because it's forced to go through
div_var_int64() instead of div_var_int() for all small divisors. So
the var2ndigits <= 2 case needs to come first.

The implementation of div_var_int64() should be in an #ifdef HAVE_INT128 block.

In div_var_int64(), s/ULONG_MAX/PG_UINT64_MAX/

Regards,
Dean