Description

markshannon

opened on Aug 18, 2021

Issue body actions

BPO	44946
Nosy	@mdickinson, @vstinner, @markshannon, @xuxinhang
PRs	bpo-44946: Streamline operators and creation of ints for common case of single 'digit'. #27832 bpo-46055: Speed up binary shifting operators #30044

^{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 = None
closed_at = <Date 2021-08-26.15:09:37.280>
created_at = <Date 2021-08-18.10:25:32.126>
labels = ['interpreter-core', 'performance']
title = 'Integer operations are inefficient for "medium" integers.'
updated_at = <Date 2021-12-11.04:39:53.226>
user = 'https://github.com/markshannon'

bugs.python.org fields:

activity = <Date 2021-12-11.04:39:53.226>
actor = 'xuxinhang'
assignee = 'none'
closed = True
closed_date = <Date 2021-08-26.15:09:37.280>
closer = 'Mark.Shannon'
components = ['Interpreter Core']
creation = <Date 2021-08-18.10:25:32.126>
creator = 'Mark.Shannon'
dependencies = []
files = []
hgrepos = []
issue_num = 44946
keywords = ['patch']
message_count = 5.0
messages = ['399832', '399833', '399834', '399838', '400263']
nosy_count = 4.0
nosy_names = ['mark.dickinson', 'vstinner', 'Mark.Shannon', 'xuxinhang']
pr_nums = ['27832', '30044']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue44946'
versions = []

Activity

1. markshannon commented on Aug 18, 2021

   

   markshannon

   on Aug 18, 2021

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   "Medium" integers are those with a single internal digit or zero.
   Medium integers are integers in the range -2**30 to +2**30 on 64 bit machines.
   "Small" integers, -5 to 256 are cached, but are represented as medium integers internally.

   To a good approximation, all integers are "medium".

   However, we make little effort to exploit that fact in the code for binary operations, which are very common operations on integers.
2. markshannon

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   performancePerformance or resource usagePerformance or resource usage

   on Aug 18, 2021
3. mdickinson commented on Aug 18, 2021

   

   mdickinson

   on Aug 18, 2021

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   We already special-case medium integers in the Objects/longobject.c code, in various places. For example for addition, here:

   cpython/Objects/longobject.c

   Lines 3070 to 3072 in 3240bc6

   	if (Py_ABS(Py_SIZE(a)) <= 1 && Py_ABS(Py_SIZE(b)) <= 1) {
   	return PyLong_FromLong(MEDIUM_VALUE(a) + MEDIUM_VALUE(b));
   	}

   Are you proposing further changes in longobject.c, or some other mechanism?
4. mdickinson commented on Aug 18, 2021

   

   mdickinson

   on Aug 18, 2021

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   See also bpo-21955, bpo-10044, and

   cpython/Python/ceval.c

   Lines 1986 to 1991 in 3240bc6

   	/* NOTE(vstinner): Please don't try to micro-optimize int+int on
   	CPython using bytecode, it is simply worthless.
   	See http://bugs.python.org/issue21955 and
   	http://bugs.python.org/issue10044 for the discussion. In short,
   	no patch shown any impact on a realistic benchmark, only a minor
   	speedup on microbenchmarks. */
5. markshannon commented on Aug 18, 2021

   

   markshannon

   on Aug 18, 2021

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   Just changes to longobject.c.

   There are still various minor inefficiencies in testing to see whether an int is a medium value, and then throwing away size information before creating result objects.

   I'm not expecting this to make much difference, but every little helps.
6. markshannon commented on Aug 25, 2021

   

   markshannon

   on Aug 25, 2021

   MemberAuthor

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   New changeset 15d50d7 by Mark Shannon in branch 'main':
   bpo-44946: Streamline operators and creation of ints for common case of single 'digit'. (GH-27832)
   15d50d7
7. markshannon

   closed this as completedon Aug 26, 2021
8. markshannon

   closed this as completedon Aug 26, 2021
9. ezio-melotti

   transferred this issue fromon Apr 10, 2022

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