Number of Bits Needed to Represent a Zero-Offset Integer

via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Mon Jan 19 04:04:38 PST 2015


As a follow-up to

http://forum.dlang.org/thread/fdfwrdtjcawprvvkoqas@forum.dlang.org#post-qxudiyoygnvvbovhjfgt:40forum.dlang.org

I'm looking for a function that figures out the number of bits 
that are needed to represent a zero-based integer:

value-set => bits
=================
0,1 => 1 (*)
0,1,2 => 2
0,1,2,3 => 2 (*)
0,1,2,3,4 => 3
0,1,2,3,4,5 => 3
0,1,2,3,4,5,6 => 3
0,1,2,3,4,5,6,7 => 3 (*)
0,1,2,3,4,5,6,7,8 => 4
...

(*) means full bit usage


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