Mark Dickinson dicki...@gmail.com added the comment:
Mike Cowlishaw has confirmed that the tests scbx164, scbx165 (in version
2.59 of the tests) are implementation-specific, so test_decimal is doing
the right thing in skipping them. So I think this issue can be closed.
I don't think it's
Mark Dickinson dicki...@gmail.com added the comment:
There's a restriction on the second argument to scaleb in the spec,
namely that scaleb should be in the range -2*(Emax + precision) to
2*(Emax + precision) inclusive.
This restriction seems entirely arbitrary and unnecessary to me. My
Changes by Mark Dickinson dicki...@gmail.com:
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priority: high - normal
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Mark Dickinson dicki...@gmail.com added the comment:
logb fix applied to release26-maint in r75804.
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Mark Dickinson dicki...@gmail.com added the comment:
Updated release26-maint to new test-suite in r75806.
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Mark Dickinson dicki...@gmail.com added the comment:
I just want to note another problem with logb: it doesn't use the correct
context when processing NaNs. This needs a test and a fix.
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Mark Dickinson dicki...@gmail.com added the comment:
Sorry; ignore that last. I was confused by the fact that the _check_nans
call came before the 'if context is None' test. But _check_nans deals
correctly with a context of None, so logb is fine.
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Mark Dickinson dicki...@gmail.com added the comment:
I've updated to the newest version of the test-suite in r75285 through
r75287. As before, r75285 needs to be backported to the 2.6 maintenance
branch once its unfrozen.
I'm currently skipping those two scaleb tests, until we work out what
Mark Dickinson dicki...@gmail.com added the comment:
(Stefan emailed Mike Cowlishaw about this: thanks, Stefan!)
Mike's initial response suggests that we *should* be rounding the result
here. That is, decNumber and decimal.py are both in error, and Stefan's
interpretation is correct.
Mark Dickinson dicki...@gmail.com added the comment:
Attaching additional testcases from Mike Cowlishaw.
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Added file: http://bugs.python.org/file15067/logb_additional.decTest
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Raymond Hettinger rhettin...@users.sourceforge.net added the comment:
Mike's response makes sense to me. If the precision is 2, the result
should round to that precision. The documents showing the theory behind
the decimal spec indicate that in general mathematical operations are
exact, only
Mark Dickinson dicki...@gmail.com added the comment:
Patch to update to the most recent official set of tests.
With this patch, logb and scaleb fail.
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keywords: +patch
Added file: http://bugs.python.org/file15070/decimal_testcases.patch
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Mark Dickinson dicki...@gmail.com added the comment:
Patch to fix logb.
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Added file: http://bugs.python.org/file15071/logb.patch
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Mark Dickinson dicki...@gmail.com added the comment:
I don't understand the new scaleb testcases (from Mike). They look like
this:
precision: 34
maxExponent: 9
minExponent: -9
-- integer overflow in 3.61 or earlier
scbx164 scaleb 1E-9 -12 - NaN
Mark Dickinson dicki...@gmail.com added the comment:
The IEEE 754-2008 description of scaleB makes a lot more sense, IMO:
scaleB(x, N) is simply x*10**N (assuming that B=10 and N is integral),
rounded in the usual way.
The restriction in the specification seems arbitrary and questionable.
Mark Dickinson dicki...@gmail.com added the comment:
Applied the fix for logb in r75275 (trunk), r75276 (py3k) and r75277
(release31-maint). r75275 still needs to be merged to the release26-maint
branch once it's unfrozen.
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Stefan Krah stefan-use...@bytereef.org added the comment:
precision: 34
maxExponent: 9
minExponent: -9
-- integer overflow in 3.61 or earlier
scbx164 scaleb 1E-9 -12 - NaN Invalid_operation
-- out of range
scbx165 scaleb -1E-9 +12 - NaN
New submission from Stefan Krah stefan-use...@bytereef.org:
from decimal import *
c = getcontext()
c.prec = 2
c.logb(Decimal(1E123456))
Decimal('123456')
This result agrees with the result of decNumber, but the spec says:
All results are exact unless an integer result does not fit in the
Mark Dickinson dicki...@gmail.com added the comment:
Hmm. The problem here is that the specification says nothing at all
about what should happen if the integer result does *not* fit in the
available precision, so in this case we went with the decNumber
behaviour.
Rather than rounding, I'd
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