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

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

I don't understand the new scaleb testcases (from Mike).  They look like 
this:

precision:   34
maxExponent: 999999999
minExponent: -999999999
-- integer overflow in 3.61 or earlier
scbx164 scaleb  1E-999999999  -1200000000  -> NaN Invalid_operation
-- out of range
scbx165 scaleb  -1E-999999999  +1200000000  -> NaN Invalid_operation

The specification says that the second operand should be in the range 
+/-2*(Emax+precision) inclusive, which in this case it is.  So clearly 
there are additional situations in which Invalid_operation should be 
signalled.  It's not clear to me what those conditions are.

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<http://bugs.python.org/issue7048>
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