[SciPy-dev] Testing for powers of two

Charles Harris charles.harris at sdl.usu.edu
Fri Oct 29 11:12:45 CDT 2004


There was a discussion some time ago about testing for powers of two.
The other day I saw a nifty version go by on the LKML, courtesy of
Linus. Namely:

is_power_of_two = x && !(x & (x - 1))

which works for all numbers except possibly the number x8000, which if
twos complement will probably give an underflow on subtraction of 1. So
for signed numbers:

is_power_of_two = x > 0 && !(x & (x - 1))

Chuck




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