[Python-checkins] bpo-29882: _Py_popcount32() doesn't need 64x64 multiply (GH-30774)

[vstinner]

https://github.com/python/cpython/commit/cd8de40b3b10311de2db7b90abdf80af9e35535f
commit: cd8de40b3b10311de2db7b90abdf80af9e35535f
branch: main
author: Victor Stinner <vstinner at python.org>
committer: vstinner <vstinner at python.org>
date: 2022-01-22T00:54:42+01:00
summary:

bpo-29882: _Py_popcount32() doesn't need 64x64 multiply (GH-30774)

32x32 bits multiply is enough for _Py_popcount32().

files:
M Include/internal/pycore_bitutils.h

diff --git a/Include/internal/pycore_bitutils.h b/Include/internal/pycore_bitutils.h
index e4aa7a3d0d056..3fd70b0e417c1 100644
--- a/Include/internal/pycore_bitutils.h
+++ b/Include/internal/pycore_bitutils.h
@@ -125,7 +125,7 @@ _Py_popcount32(uint32_t x)
     // Put count of each 8 bits into those 8 bits
     x = (x + (x >> 4)) & M4;
     // Sum of the 4 byte counts
-    return (uint32_t)((uint64_t)x * (uint64_t)SUM) >> 24;
+    return (x * SUM) >> 24;
 #endif
 }