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Give a one-line C expression to test whether a number is a power of 2. [No loops allowed]?

Posted 6-Sep-12 23:45pm

Surendra0x2

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JackDingler 7-Sep-12 13:27pm

Hope you get an A on your homework.

Chuck O'Toole 7-Sep-12 16:16pm

Amazing coincidence, the link in solution 2 below is to a question that is worded exactly the same but posted in November of 2005 :) I guess they're still using the same homework questions almost 7 years later.

3 solutions

Solution 4

return (v % 2 == 0 ? true : false);

Posted 7-Sep-12 4:30am

basementman

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Chuck O'Toole 7-Sep-12 15:54pm

Nope, that's a test for even / odd, multiple of 2 not power of 2

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pasztorpisti · Accepted Answer · 2012-09-07T00:01:00

Solution 3

C++

v && !(v & (v - 1));

Source: http://graphics.stanford.edu/~seander/bithacks.html[^]

Posted 7-Sep-12 0:01am

pasztorpisti

Comments

Espen Harlinn 7-Sep-12 8:31am

5'ed!

pasztorpisti 7-Sep-12 8:42am

Thank you!

Chuck O'Toole 7-Sep-12 15:55pm

Assumes "v" is an integer type, doesn't work across the board for float / double

**JF2015** · Accepted Answer · 2012-09-06T23:59:00

Solution 2

C#

isPow2 = x && !( (x-1) & x );

See here for an explanation:
http://bytes.com/topic/c/answers/213306-test-whether-number-power-2-a[^]

Posted 6-Sep-12 23:59pm

JF2015

Comments

Philip Stuyck 7-Sep-12 6:08am

This is better than my logarithmic solution, which I deleted since this is really better. +5

Espen Harlinn 7-Sep-12 8:31am

5'ed!

JackDingler 7-Sep-12 13:26pm

Clever

Chuck O'Toole 7-Sep-12 15:53pm

Assumes "x" is an integer type, doesn't work across the board for float / double