[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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 worth removing the res

[issue7048] decimal.py: logb: round the result if it is greater than prec

Changes by Mark Dickinson : -- priority: high -> normal ___ Python tracker ___ ___ Python-bugs-list mailing list Unsubscribe: http://m

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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 guess is that it's ther

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson added the comment: Updated release26-maint to new test-suite in r75806. -- ___ Python tracker ___ ___ Python-bugs-list

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson added the comment: logb fix applied to release26-maint in r75804. -- ___ Python tracker ___ ___ Python-bugs-list mailin

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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. -- ___ Python tra

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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. -- ___ Python tracker __

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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 should be going on

[issue7048] decimal.py: logb: round the result if it is greater than prec

Stefan Krah 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 Invalid_operation I would s

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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. -- ___ Python tracker

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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. Presumably it's inten

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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 Invalid_operation -- out of r

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson added the comment: Patch to fix logb. -- Added file: http://bugs.python.org/file15071/logb.patch ___ Python tracker ___ ___

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson added the comment: Patch to update to the most recent official set of tests. With this patch, logb and scaleb fail. -- keywords: +patch Added file: http://bugs.python.org/file15070/decimal_testcases.patch ___ Python tracker

[issue7048] decimal.py: logb: round the result if it is greater than prec

Raymond Hettinger 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 the results get rounded. Also II

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson added the comment: Attaching additional testcases from Mike Cowlishaw. -- Added file: http://bugs.python.org/file15067/logb_additional.decTest ___ Python tracker _

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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. -- assignee: -> m

[issue7048] decimal.py: logb: round the result if it is greater than prec

Mark Dickinson 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 say that a more use

[issue7048] decimal.py: logb: round the result if it is greater than prec

New submission from Stefan Krah : >>> 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 available