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bpo-45569: Change PYLONG_BITS_IN_DIGIT default to 30 (GH-30497)

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Mark Dickinson 2022-01-14 18:54:56 +00:00 committed by GitHub
parent ee1a8b336d
commit 025cbe7a9b
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6 changed files with 22 additions and 16 deletions
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3
Doc/using/configure.rst
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@ -35,8 +35,7 @@ General Options
Define the size in bits of Python :class:`int` digits: 15 or 30 bits.
By default, the number of bits is selected depending on ``sizeof(void*)``:
30 bits if ``void*`` size is 64-bit or larger, 15 bits otherwise.
By default, the digit size is 30.
Define the ``PYLONG_BITS_IN_DIGIT`` to ``15`` or ``30``.

10
Doc/whatsnew/3.11.rst
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@ -622,6 +622,16 @@ Build Changes
like Pyodide.
(Contributed by Christian Heimes and Ethan Smith in :issue:`40280`.)
* CPython will now use 30-bit digits by default for the Python :class:`int`
implementation. Previously, the default was to use 30-bit digits on platforms
with ``SIZEOF_VOID_P >= 8``, and 15-bit digits otherwise. It's still possible
to explicitly request use of 15-bit digits via either the
``--enable-big-digits`` option to the configure script or (for Windows) the
``PYLONG_BITS_IN_DIGIT`` variable in ``PC/pyconfig.h``, but this option may
be removed at some point in the future. (Contributed by Mark Dickinson in
:issue:`45569`.)
C API Changes
=============

16
Include/pyport.h
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@ -85,20 +85,12 @@ Used in: Py_SAFE_DOWNCAST
#define PY_INT32_T int32_t
#define PY_INT64_T int64_t
/* If PYLONG_BITS_IN_DIGIT is not defined then we'll use 30-bit digits if all
the necessary integer types are available, and we're on a 64-bit platform
(as determined by SIZEOF_VOID_P); otherwise we use 15-bit digits.
From pyodide: WASM has 32 bit pointers but has native 64 bit arithmetic
so it is more efficient to use 30 bit digits.
/* PYLONG_BITS_IN_DIGIT describes the number of bits per "digit" (limb) in the
* PyLongObject implementation (longintrepr.h). It's currently either 30 or 15,
* defaulting to 30. The 15-bit digit option may be removed in the future.
*/
#ifndef PYLONG_BITS_IN_DIGIT
#if SIZEOF_VOID_P >= 8 || defined(__wasm__)
# define PYLONG_BITS_IN_DIGIT 30
#else
# define PYLONG_BITS_IN_DIGIT 15
#endif
#define PYLONG_BITS_IN_DIGIT 30
#endif
/* uintptr_t is the C9X name for an unsigned integral type such that a

5
Misc/NEWS.d/next/Build/2022-01-09-11-24-54.bpo-45569.zCIENy.rst Normal file
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@ -0,0 +1,5 @@
The build now defaults to using 30-bit digits for Python integers. Previously
either 15-bit or 30-bit digits would be selected, depending on the platform.
15-bit digits may still be selected using the ``--enable-big-digits=15`` option
to the ``configure`` script, or by defining ``PYLONG_BITS_IN_DIGIT`` in
``pyconfig.h``.

2
configure vendored
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@ -1730,7 +1730,7 @@ Optional Features:
Doc/library/socket.rst (default is yes if supported)
--enable-big-digits[=15|30]
use big digits (30 or 15 bits) for Python longs
(default is system-dependent)]
(default is 30)]
--disable-test-modules don't build nor install test modules
Optional Packages:

2
configure.ac
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@ -5084,7 +5084,7 @@ AC_CHECK_DECLS([RTLD_LAZY, RTLD_NOW, RTLD_GLOBAL, RTLD_LOCAL, RTLD_NODELETE, RTL
# determine what size digit to use for Python's longs
AC_MSG_CHECKING([digit size for Python's longs])
AC_ARG_ENABLE(big-digits,
AS_HELP_STRING([--enable-big-digits@<:@=15|30@:>@],[use big digits (30 or 15 bits) for Python longs (default is system-dependent)]]),
AS_HELP_STRING([--enable-big-digits@<:@=15|30@:>@],[use big digits (30 or 15 bits) for Python longs (default is 30)]]),
[case $enable_big_digits in
yes)
enable_big_digits=30 ;;