Add audioop.byteswap()

[serhiy-storchaka]

BPO	19641
Nosy	@serhiy-storchaka
Files	audioop_byteswap.patch audioop_byteswap_2.patch audioop_byteswap_3.patch

^{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/serhiy-storchaka'
closed_at = <Date 2013-11-23.20:29:14.138>
created_at = <Date 2013-11-18.10:25:07.337>
labels = ['type-feature', 'library']
title = 'Add audioop.byteswap()'
updated_at = <Date 2013-11-23.20:29:14.136>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2013-11-23.20:29:14.136>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2013-11-23.20:29:14.138>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2013-11-18.10:25:07.337>
creator = 'serhiy.storchaka'
dependencies = []
files = ['32686', '32688', '32749']
hgrepos = []
issue_num = 19641
keywords = ['patch']
message_count = 5.0
messages = ['203273', '203284', '203601', '204100', '204101']
nosy_count = 2.0
nosy_names = ['python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue19641'
versions = ['Python 3.4']

[serhiy-storchaka]

The audio modules often need convert between little endian and big endian data. The array module can be used to byteswap 16- and 32-bit samples, but it can't help with 24-bit samples. Python implemented function for swapping bytes is not very efficient. In any case the use of array is not so simple (see bpo-19276, bpo-19633).

The proposed patch adds efficient byteswap() function in the audioop module. byteswap(fragment, width) byteswaps every "width"-byte sample in the fragment and returns modified data.

[serhiy-storchaka]

Updated patch addresses some Victor's comments. Added optimization for trivial case byteswap(bytes, 1).

[serhiy-storchaka]

The patch is synchronized with tip (after committing bpo-19633). It enables temporary disabled in bpo-19633 tests.

[python-dev]

New changeset fbebc90abcd1 by Serhiy Storchaka in branch 'default':
Issue bpo-19641: Added the audioop.byteswap() function to convert big-endian
http://hg.python.org/cpython/rev/fbebc90abcd1

[serhiy-storchaka]

I have committed simplified patch, without optimization for 1-byte samples.