[emirplus]

Fixes #160050.

In Objects/longobject.c, l_divmod switches to pylong_int_divmod() when operands exceed the threshold (size_w > 300 && (size_v - size_w) > 150), providing asymptotically faster division. However, l_mod() bypassed this fast path and fell through directly to long_rem(), resulting in integer modulo (%) taking significantly longer than divmod(a, b)[1] for large integers.

This patch adds the same WITH_PYLONG_MODULE threshold check in l_mod(), invoking pylong_int_divmod(v, w, NULL, pmod) when sizes exceed the threshold.

Benchmark

Using the benchmark from the issue with operands where bits = 128_000:

• Before: // = 0.0105s, % = 0.0224s, divmod = 0.0083s (modulo ~2.1x slower than integer division)
• After: // = 0.0088s, % = 0.0093s, divmod = 0.0098s (modulo has matching complexity)

Testing

• Added test_pylong_int_mod in Lib/test/test_int.py.
• Extended test_pylong_int_divmod_crash to cover %.
• Verified all tests pass with ./PCbuild/amd64/python.exe -m test test_int test_long.

• Issue: modulo for huge integers has the wrong complexity #160050

[python-cla-bot]

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