The function ulong_from_little_endian is endian-agnostic and was tested by forcing is_big_endian=1 on a little-endian system.

Since this PR seems to give performance on par with gmpy2 it is unclear whether PEP 757 will be even necessary. I have not been able to build #64 for comparison

Also, it should work with older Python versions.

The PEP 757 interface is provided as CPython's best effort to give something efficient for this using public API in Python 3.14 onwards. I think that should be the baseline before trying any other approach.

Interesting, conversion to int seems asymptotically faster with this approach (c.f. using mpz_export). Perhaps, it could be a little better with new PyLong_*Bytes*() C-API. Below my benchmarks. I would appreciate if someone could repeat this on less noisy system.

AFAIK gmpy2 uses private Python stuff already so it might be difficult to do better.

No, gmpy2 uses PEP 757 API (using pythoncapi-compat for <3.14).

Import (int -> mpz)

Export (mpz -> int)

Could someone trigger CI tests in this pr (build logs are expired)?

# bench-import.py

import os

import pyperf

_T = os.getenv('_T')
if _T == "gmpy2.mpz":
    from gmpy2 import mpz
elif _T == "gmp.mpz":
    from gmp import mpz
else:
    from flint import fmpz as mpz

cases = ['1<<7', '1<<38', '1<<300', '1<<3000', '1<<10000']
runner = pyperf.Runner()
for c in cases:
    i = eval(c)
    runner.bench_func(c, mpz, i)

# bench-export.py

import os

import pyperf

_T = os.getenv('_T')
if _T == "gmpy2.mpz":
    from gmpy2 import mpz
elif _T == "gmp.mpz":
    from gmp import mpz
else:
    from flint import fmpz as mpz

cases = ['1<<7', '1<<38', '1<<300', '1<<3000', '1<<10000']
runner = pyperf.Runner()
for c in cases:
    i = eval(c)
    m = mpz(i)
    runner.bench_func(c, int, m)

gmpy2 uses PEP 757 API (using pythoncapi-compat for <3.14).

I think that python-flint should do the same.

After timings above and in gh-358 I think it turns out that the approach in this PR is the best one for python-flint. For now it seems that PEP 757 along with GMP's import/export functions is slower than using to_bytes and from_bytes.

CI checks here should pass after gh-359

Okay, looks good. Well get this in for now and can consider later if any other approach seems to time faster.