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Inconsistency with PyLong_FromVoidPtr() and PyLong_AsVoidPtr() #60484

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serhiy-storchaka opened this issue Oct 18, 2012 · 3 comments
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Inconsistency with PyLong_FromVoidPtr() and PyLong_AsVoidPtr() #60484

serhiy-storchaka opened this issue Oct 18, 2012 · 3 comments
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@mdickinson
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interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error

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@serhiy-storchaka
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BPO 16280
Nosy @mdickinson, @serhiy-storchaka

Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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GitHub fields:

assignee = 'https://github.com/mdickinson'
closed_at = <Date 2012-10-18.21:31:56.992>
created_at = <Date 2012-10-18.20:36:45.724>
labels = ['interpreter-core', 'type-bug']
title = 'Inconsistency with PyLong_FromVoidPtr() and PyLong_AsVoidPtr()'
updated_at = <Date 2012-10-18.21:31:56.991>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2012-10-18.21:31:56.991>
actor = 'mark.dickinson'
assignee = 'mark.dickinson'
closed = True
closed_date = <Date 2012-10-18.21:31:56.992>
closer = 'mark.dickinson'
components = ['Interpreter Core']
creation = <Date 2012-10-18.20:36:45.724>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 16280
keywords = []
message_count = 3.0
messages = ['173295', '173297', '173298']
nosy_count = 3.0
nosy_names = ['mark.dickinson', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue16280'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3', 'Python 3.4']
@serhiy-storchaka
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This issue is taken out of the discussion of bpo-16277.

PyLong_FromVoidPtr() has special case which maps null pointer to zero integer.

On platforms where (uintptr_t)(void *)0 is 0, this code has no effect and is redundant. But on hypothetic platforms where (uintptr_t)(void *)0 is not 0, PyLong_FromVoidPtr() maps NULL to 0 and then PyLong_AsVoidPtr() maps 0 to non-NULL. Also PyLong_FromVoidPtr() is multivalued, it maps to 0 NULL and may be some other pointer.

PyLong_FromVoidPtr() in 2.7 has special case only on platform where sizeof(void*) > sizeof(long). It commented as "optimize null pointers". In 3.x branch such optimization non needed because PyLong_FromUnsignedLongLong() already has special case for short integers.

The solution of this issue is getting rid of a special case, or adding a special case in PyLong_FromVoidPtr(). It is desirable to make it avoiding multivaluedity.

@serhiy-storchaka serhiy-storchaka added performance Performance or resource usage interpreter-core (Objects, Python, Grammar, and Parser dirs) labels Oct 18, 2012
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python-dev mannequin commented Oct 18, 2012

New changeset 5ae4ff03b35f by Mark Dickinson in branch 'default':
bpo-16280: Drop questionable special-casing of null pointer in PyLong_FromVoidPtr.
http://hg.python.org/cpython/rev/5ae4ff03b35f

@mdickinson
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Dropped the special case for 3.4. I'm leaving the code as-is for the maintenance branches, as discussed in bpo-16277.

@mdickinson mdickinson self-assigned this Oct 18, 2012
@mdickinson mdickinson added type-bug An unexpected behavior, bug, or error and removed performance Performance or resource usage labels Oct 18, 2012
@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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