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bpo-29882: Add _Py_popcount32() function (GH-20518)

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* 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().
This commit is contained in:
Victor Stinner 2020-06-08 16:30:33 +02:00 • committed by GitHub
parent 301f0d4ff9
commit c6b292cdee
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11 changed files with 108 additions and 39 deletions
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15
Objects/longobject.c
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@ -3,8 +3,9 @@
/* XXX The functional organization of this file is terrible */
#include "Python.h"
#include "pycore_interp.h" // _PY_NSMALLPOSINTS
#include "pycore_pystate.h" // _Py_IsMainInterpreter()
#include "pycore_bitutils.h" // _Py_popcount32()
#include "pycore_interp.h" // _PY_NSMALLPOSINTS
#include "pycore_pystate.h" // _Py_IsMainInterpreter()
#include "longintrepr.h"
#include <float.h>
@ -5307,12 +5308,10 @@ int_bit_length_impl(PyObject *self)
static int
popcount_digit(digit d)
{
/* 32bit SWAR popcount. */
uint32_t u = d;
u -= (u >> 1) & 0x55555555U;
u = (u & 0x33333333U) + ((u >> 2) & 0x33333333U);
u = (u + (u >> 4)) & 0x0f0f0f0fU;
return (uint32_t)(u * 0x01010101U) >> 24;
// digit can be larger than uint32_t, but only PyLong_SHIFT bits
// of it will be ever used.
Py_BUILD_ASSERT(PyLong_SHIFT <= 32);
return _Py_popcount32((uint32_t)d);
}
/*[clinic input]

2
Objects/stringlib/codecs.h
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@ -4,7 +4,7 @@
# error "codecs.h is specific to Unicode"
#endif
#include "pycore_byteswap.h" // _Py_bswap32()
#include "pycore_bitutils.h" // _Py_bswap32()
/* Mask to quickly check whether a C 'long' contains a
non-ASCII, UTF8-encoded char. */