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Bitwise NOT Operator for Sage?

asked 2014-08-18 16:30:28 -0500

david8381 gravatar image

0b1000 & 0b1001 (AND) 0b1000 | 0b1001 (OR) 0b1000 ^^ 0b1001 (XOR)

All of these work as bitwise operators on the command line -- but how do I do bitwise NOT?

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answered 2014-08-18 17:21:15 -0500

tmonteil gravatar image

updated 2014-08-18 17:22:30 -0500

The bitwise not in Python is supposed to be ~(see https://wiki.python.org/moin/BitwiseO... about how negative numbers are encoded), but Sage's preparser first transforms 0b1000 as an element of ZZ for which the action of ~ is the multiplicative inverse:

sage: ~0b1000
1/8

This is because, in Sage:

sage: 0b1000.parent()
Integer Ring
sage: preparse("0b1000")
"Integer('1000', 2)"

To get the python behaviour, you can either turn the sage preparser off:

sage: preparser(False)
sage: ~0b1000
-9

or explicitely use python int:

sage: ~int(0b1000)
-9

Another workaround is to notice that not a is the same as a xor 1.

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answered 2014-08-20 04:42:54 -0500

As a complement to @tmonteil's answer, you can append 'r' (for 'raw') to some input to prevent it from being preparsed, without globally turning the preparser off.

Using the same example as @tmonteil:

sage: ~0b1000r
-9
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Asked: 2014-08-18 16:30:28 -0500

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Last updated: Aug 20 '14