[Python-bugs-list] [ python-Bugs-660455 ] -hex/oct const generates wrong code

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Bugs item #660455, was opened at 2002-12-31 13:11
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Category: Parser/Compiler
Group: Python 2.2
Status: Open
Resolution: None
Priority: 6
Submitted By: Guido van Rossum (gvanrossum)
Assigned to: Nobody/Anonymous (nobody)
Summary: -hex/oct const generates wrong code

Initial Comment:
Since Python 2.2, there's code in com_factor() in
compile.c that expands negative constants inline. For
example, the expression -1 generates a single
LOAD_CONST opcode for -1, rather than (as in Python 2.1
and before) generating a LOAD_CONST for +1 followed by
a UNARY_NEGATIVE opcode.

Unfortunately there's an end case where this causes
surprising behavior: when the constant is an octal or
hexadecimal constant that already has a negative value
(despite having no sign), the generated code yields a
different result than expected.  For example:

>>> print -(0xffffffff)
1
>>> x = 0xffffffff 
>>> print -x
1
>>> print -0xffffffff 
-4294967295
>>> 

Despite the fact that in Python 2.4 (!) all of these
will print the third outcome, in Python 2.2 and 2.3, I
think the third outcome is wrong and unexpected.

No time to fix this for 2.3a1, but should fix it before
2.3a2.

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