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Editorial Team
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Asked: 2026-06-09T13:43:57+00:00

Given offset OFF and length LEN, isolate a group of bits and shift it

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Given offset OFF and length LEN, isolate a group of bits and shift it to the right. (Usage: int holding several smaller-range integers with given offsets and lengths). For example using offset 4 and length 4, 

  a = 110101011000
      ----^^^^---- this is the group 
      000000000101
              ^^^^ isolated and right-shifted here

I currently use

(a>>OFF)&((1<<(LEN+1))-1)

giving for the example above

a                         110101011000
a>>OFF                    000011010101
1<<(LEN+1)                000000010000
1<<(LEN+1)-1              000000001111
(a>>OFF)&((1<<(LEN+1))-1) 000000000101

Is there a more readable/efficient way?

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1 Answer

  1. Editorial Team

    There isn’t a single correct answer in this case. What you did is fine – it’s correct, and with some documentation it’s also pretty clear.

    If you want different ways, you can: try shifting a left and then right again (assuming a is unsigned – otherwise cast it first); or you can first create a mask (in your case: 000011110000), bitwise-and, and only then shift. However, these won’t necessarily be prettier than what you already have.

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