bpo-29882: Add _Py_popcount32() function by vstinner · Pull Request #20518

bpo-29882: Add _Py_popcount32() function by vstinner · Pull Request #20518 · python/cpython

* Rename pycore_byteswap.h to pycore_bitutils.h.
* Move popcount_digit() to pycore_bitutils.h as _Py_popcount32().
* _Py_popcount32() uses GCC and clang builtin function if available.
* Add unit tests to _Py_popcount32().

* Remove UINT32_C()
* Fix #ifdef to decide if builtin functions are used of not:
  use SIZEOF_INT >= 4. Always use __builtin_popcountl() otherwise.
* popcount_digit(): check PyLong_SHIFT rather than sizeof(digit).
* Fix also two comments

niklasf added a commit to niklasf/cpython that referenced this pull request

Jun 8, 2020

In pythonGH-2866, _Py_Bit_Length() was added to pymath.h for lack of a better
location. pythonGH-20518 added a more appropriate header file for bit utilities. It
also shows how to properly use intrinsics. This allows reconsidering bpo-29782.

* Move the function to the new header.
* Changed return type to match __builtin_clzl and reviewed usage.
* Use intrinsics where available.
* Pick a (mostly theoretical) fallback implementation suitable for
  inlining.

vstinner pushed a commit that referenced this pull request

Jun 15, 2020

In GH-2866, _Py_Bit_Length() was added to pymath.h for lack of a better
location. GH-20518 added a more appropriate header file for bit utilities. It
also shows how to properly use intrinsics. This allows reconsidering bpo-29782.

* Move the function to the new header.
* Changed return type to match __builtin_clzl() and reviewed usage.
* Use intrinsics where available.
* Pick a fallback implementation suitable for inlining.

This was referenced

Jan 22, 2022

niklasf mannequin mentioned this pull request

Nov 13, 2022