C# how to get the index of bit

Question

2.50/5 (2 votes)

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I want to get the index of the first bit that equal to 1, and the index of the last bit that equal to 1. For example:

data=0x3E

first bit = 1

last bit = 5

How can I do this?

Posted 13-Feb-14 10:41am

Member 10304617

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Andreas Gieriet 13-Feb-14 16:44pm

Have you already tried something? E.g. probing? What you need is shifting and bit-and (and counting).
Cheers
Andi

Member 10304617 13-Feb-14 16:47pm

first and last bit that turn on

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Andreas Gieriet · Accepted Answer · 2014-02-13T10:52:00

Solution 1

Pseudo code:

function get_lowest_bit(in input, out bit_pos) returns true if input is not 0, false otherwise
  for bit_pos = 0 to max_bits-1
    if (input bit_and (1 left_shift bit_pos) not_equal 0
       return true
    end if
  end for
  return false
end function

Likewise for the upper bit.
Cheers
Andi
PS: I assume this is a homework, that's why I do not give you the C# solution and leave the exercise for the highest bit for you ;-)

Posted 13-Feb-14 10:52am

Andreas Gieriet

Updated 13-Feb-14 10:55am

v2

Comments

Member 10304617 13-Feb-14 16:56pm

sorry, but i did not understand the code.
what is max_bit?
and what do you ask in the if()...?

Andreas Gieriet 13-Feb-14 17:44pm

I think you have to figure out that yourself. Requires basic understanding of C# types. E.g. if the type of your variable is int, replace max_bits by the number of bits for type int. The terms bit_and, left_shift, not_equal can be looked up in your text book or in google. How to write a for-loop, a function, and an if-statement is also basic C# knowledge that will not be explained here by anyone.
Cheers
Andi

Member 10304617 13-Feb-14 18:27pm

I know C# very well.

Andreas Gieriet 13-Feb-14 18:29pm

Hm, then I wonder why the question...
Anyways, seems you get it done somehow, then.
Cheers
Andi

Sergey Alexandrovich Kryukov 13-Feb-14 17:21pm

5ed... :-)
—SA

Andreas Gieriet 13-Feb-14 17:39pm

Thanks for your 5!
Cheers
Andi

Member 10304617 13-Feb-14 17:28pm

Ok,thanks!
will I have a test on this? ;)

Andreas Gieriet 13-Feb-14 17:40pm

Well, the test could be: transform this pseudo code into concrete C# code. ;-)
Good luck!
Cheers
Andi