[RFC] Adding division/modulo on arbitrary precision integers to libgcc

[Jakub Jelinek]

On Fri, May 06, 2022 at 02:09:21PM +0000, Matthias Gehre via Gcc wrote:
> /// \param quo The quotient represented by n words. Must be non-null.
> /// \param rem The remainder represented by n words. Must be non-null.
> /// \param a The dividend represented by n + 1 words. Must be non-null.
> /// \param b The divisor represented by n words. Must be non-null.
> 
> /// \note The word order is in host endianness.
> /// \note Might modify a and b.
> /// \note The storage of 'a' needs to hold n + 1 elements because some
> ///       implementations need extra scratch space in the most significant word.
> ///       The value of that word is ignored.
> void __udivmodei5(uint32_t *quo, uint32_t *rem, uint32_t *a,
>                                   uint32_t *b, unsigned n);
> 
> /// Computes the signed division of a / b.
> /// See __udivmodei5 for details.
> void __divmodei5(uint32_t *quo, uint32_t *rem, uint32_t *a, uint32_t *b,
>                                  unsigned n);

Sizes certainly should be with size_t, not unsigned type.
Rather than uint32_t, wouldn't using the word size (64-bit for lp64, 32-bit
for ilp32) be better?
And I really don't like the N + 1 stuff you're proposing, at least for
_BigInts that would be represented as an array of those word etc. elements
from least to most significant (or vice versa?  That really needs to be
specified too), if they are same precision having to copy one of them just
to get the extra scratch is bad.

	Jakub