Getting the n-th bit of a integer

Learning
1

Hello there,

Do you know any way to get the nth bit of an integer?

Obviously I can (and I do) use “Int.shift_right” and “mod 2”, but it is probably not the best way to do so, unless the compiler is able to handle such an operation well.

2

(Edited by hand, because the link was dropped during the e-mail transmission. Sorry)

Here is a nice reference (Not related to OCaml) that may help:

http://graphics.stanford.edu/~seander/bithacks.html

Best regards

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3

You should use land 1 instead of mod 2. Other than that, there is not much you can do to improve the generated code.

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4

Agreed. One reason is that x mod 2 can return -1 if x is negative…

If you want the bit as a Boolean instead of an integer, ((x lsr n) land 1) <> 0 should work fine.

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5

Prepare one mask value for each n and then bitwise-and the mask with your int.

6

Have you measured the relevance of further performance improvement? Can you provide the figures?

And what do you mean by ‘well’?