Hello!
We would like to add support for division/modulo on large arbitrary precision
integers to libgcc/compiler-rt
as required by C23's _BitInt type [0].
>From what I know, gcc doesn't yet support C23 _BitInt, but we would still
like to ensure that libgcc and compiler-rt can stay compatible in the future.
We created a prototype in compiler-rt [1], which uses the following
declarations:
/// Computes the unsigned division of a / b for two large integers
/// composed of n significant words.
/// Writes the quotient to quo and the remainder to rem.
///
/// \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);
The current prototype requires the compiler backend to first promote large
integers to a multiple of 32 bits.
The extra word of storage in argument `a` is required to allow implementations
to use Knuth's
algorithm efficiently.
We are not fixed on the current function prototypes, and would like
to take your feedback.
E.g. is the naming of the functions in line with the scheme used by libgcc?
Best wishes,
Matthias
CC'ing Martin Liska as recommended by MaskRay on the PR
[0] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2763.pdf
[1] https://reviews.llvm.org/D120327#change-mseSeWmhjTZf
Dr. Matthias Gehre
SMTS Software Development Engineer | AMD
Adaptive Computing Tools
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