Integer bit operations performance improvement.

[jafo]

BPO	1492860
Nosy	@tim-one, @mdickinson, @pitrou, @devdanzin

^{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 2009-04-29.09:18:16.560>
created_at = <Date 2006-05-22.11:43:04.000>
labels = ['interpreter-core', 'easy', 'performance']
title = 'Integer bit operations performance improvement.'
updated_at = <Date 2009-04-29.09:18:16.559>
user = 'https://bugs.python.org/jafo'

bugs.python.org fields:

activity = <Date 2009-04-29.09:18:16.559>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2009-04-29.09:18:16.560>
closer = 'mark.dickinson'
components = ['Interpreter Core']
creation = <Date 2006-05-22.11:43:04.000>
creator = 'jafo'
dependencies = []
files = []
hgrepos = []
issue_num = 1492860
keywords = ['easy']
message_count = 8.0
messages = ['54813', '54814', '83937', '86584', '86678', '86754', '86768', '86787']
nosy_count = 5.0
nosy_names = ['tim.peters', 'jafo', 'mark.dickinson', 'pitrou', 'ajaksu2']
pr_nums = []
priority = 'low'
resolution = 'rejected'
stage = 'needs patch'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue1492860'
versions = ['Python 2.7']

[jafo]

At the Need for Speed sprint, Tim Peters asked if
anyone had any need for integer bit operation
performance improvement. Apparently, it's easy to
improve, but nobody has said they need this. Please
reply to this task if you have an application which
needs this.

[tim-one]

Logged In: YES
user_id=31435

Changed Category to Performance. The idea with this one is
that the eval loop could easily inline "int & int", "int |
int", "int ^ int", much as it inlines "int + int" today.

[mdickinson]

To see what Tim's talking about here, see the 'big switch' ("switch
opcode") in function PyEval_EvalFrameEx in Python/ceval.c, and look at the
"case BINARY_ADD" bit. Inlining the bitwise operators should be even
easier, since there are no overflow worries. (We do have to assume that C
longs are two's-complement with no trap representation, but
Objects/intobject.c does that already, so it's probably okay.)

This only applies to 'short' integers, so I don't think it's relevant for
Python 3.x.

[devdanzin]

There's a related patch in bpo-1087418.

[mdickinson]

I agree bpo-1087418 is related, but why is it marked as a dependency for
this issue? It seems to me that either of these feature requests could be
implemented independently of the other: this one applies only to 2.x
ints, while bpo-1087418 applies only to 2.x longs and 3.x ints.

[devdanzin]

Mark: it was just my cluelessness showing :)

[pitrou]

I don't think it's a good thing to special-case bitwise operations in
the ceval loop. It will make the whole thing less instruction
cache-friendly, just for the purpose of speeding up some very uncommon
operations.