Decimal.max(NaN, x) gives incorrect results when x is finite and long

[mdickinson]

BPO	4084
Nosy	@loewis, @facundobatista, @mdickinson
Files	decimal_maxbug.patch: Fix for this issue

^{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 2008-12-11.09:25:20.564>
created_at = <Date 2008-10-09.08:43:16.990>
labels = ['type-bug']
title = 'Decimal.max(NaN, x) gives incorrect results when x is finite and long'
updated_at = <Date 2008-12-11.09:25:20.562>
user = 'https://github.com/mdickinson'

bugs.python.org fields:

activity = <Date 2008-12-11.09:25:20.562>
actor = 'mark.dickinson'
assignee = 'mark.dickinson'
closed = True
closed_date = <Date 2008-12-11.09:25:20.564>
closer = 'mark.dickinson'
components = []
creation = <Date 2008-10-09.08:43:16.990>
creator = 'mark.dickinson'
dependencies = []
files = ['11753']
hgrepos = []
issue_num = 4084
keywords = ['patch']
message_count = 6.0
messages = ['74557', '77518', '77589', '77594', '77600', '77601']
nosy_count = 3.0
nosy_names = ['loewis', 'facundobatista', 'mark.dickinson']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue4084'
versions = ['Python 2.6', 'Python 3.0']

[mdickinson]

Here's a snippet from Python 2.6:

>>> from decimal import Decimal, getcontext
>>> getcontext().prec = 3
>>> Decimal('NaN').max(Decimal('1234'))
Decimal('sNaN234')

The result here should be Decimal('1.23E+3')---the specification says that
the result of comparing a quiet NaN with a finite value should be that
finite value, rounded according to the context.

This also affects min, max_mag and min_mag.

The cause is that non-NaNs are incorrectly being passed to the _fix_nan
method. The attached patch fixes this, and adds new testcases to
extra.decTest to stop it happening again.

It would be good to get this fix into 3.0, if possible. I think it should
also be backported to 2.5.3.

[loewis]

Unless Facundo or some of the other decimal contributors reviews and
applies this patch really quickly, it is out of scope for 2.5.3.

[facundobatista]

Commited in trunk and Py3, thanks Mark!

Please, could you commit it in 2.5? The only change I've made in the
patch is adding the issue number to Misc/NEWS, the rest is ok.

After that, just close this.

Thanks again!

[loewis]

Mark, if you want to backport this, please go ahead. If want me to,
assign to me.

[mdickinson]

Committed, r67699. Thanks!

Leaving open because I still need to merge this to the 3.0 and 2.6
maintenance branches.

[mdickinson]

Merged to 2.6 and 3.0 maintenance branches (r67700, r67701).