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Title: gh-151289: optimize shrinking wide int subtraction by KRRT7 · Pull Request #151290 · python/cpython · GitHub

Open Graph Title: gh-151289: optimize shrinking wide int subtraction by KRRT7 · Pull Request #151290 · python/cpython

X Title: gh-151289: optimize shrinking wide int subtraction by KRRT7 · Pull Request #151290 · python/cpython

Description: This specializes exact int subtraction for a narrow but useful case: on 30-bit-digit builds, when both operands are non-compact 2- or 3-digit PyLong objects with the same sign and top digit, subtraction often shrinks the result. The specialized path computes that result directly instead of using generic long subtraction. This does not add a general wide-integer fast path, and compact subtraction remains on its existing path. Non-matching operands deopt/fall back to the existing implementation. On an Ubuntu x86-64 host (GCC 15.2, 8 logical CPUs), corrected pyperf measurements were: Case Main PR Compact subtraction 7.56 ns 7.82 ns Shrinking wide subtraction 16.2 ns 10.7 ns (1.52x faster) Non-shrinking wide subtraction 18.1 ns 18.5 ns Wide addition 18.2 ns 18.5 ns The compact, non-shrinking, and addition differences were not statistically significant in this run. A representative eight-benchmark pyperformance subset showed no significant geometric-mean change.

Open Graph Description: This specializes exact int subtraction for a narrow but useful case: on 30-bit-digit builds, when both operands are non-compact 2- or 3-digit PyLong objects with the same sign and top digit, subtra...

X Description: This specializes exact int subtraction for a narrow but useful case: on 30-bit-digit builds, when both operands are non-compact 2- or 3-digit PyLong objects with the same sign and top digit, subtra...

Opengraph URL: https://github.com/python/cpython/pull/151290

X: @github

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