Need a function to retrieve a bit value

• Mark Shvarts 1

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  Points: 5702

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  July 29, 2008 at 5:03 pm

  #190379

  We have a bigint number (64 bits), and I need to retrive a bit value ( 1 or 0) for a given bit number. What is the most efficient way to do it ?

  Thanks

• flinzer

  SSC Veteran

  Points: 295

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  August 8, 2008 at 3:46 am

  #855001

  If your bit numbering starts from right to left, this could be what you need:

  declare @Value bigint, -- The value we want to analyse

  @BitToTest tinyint -- The number of the bit we want to test (starting with 0)

  set @Value = 123456789 -- Binary: 111010110111100110100010101 (left out leading 0s)

  -- We have to:

  -- * Create a mask (bigint), i.e. 1 shifted to left @BitToTest times

  -- A left shift is easyly implemented using powers of 2

  -- * AND the mask with the @Value

  -- * Convert the result to bit

  -- For example we want to test bit 7 (the 8th bit from the right side), which should be 0

  set @BitToTest = 7

  select CAST(@Value & POWER(2, @BitToTest) as bit) 'BitSet?'

  /* Result

  BitSet?

  -------

  0

  (1 Row(s) affected)

  */

  -- Other example: Test bit 4 (the 5th bit from the right side), which should be 1

  set @BitToTest = 4

  select CAST(@Value & POWER(2, @BitToTest) as bit) 'BitSet?'

  /* Result:

  BitSet?

  -------

  1

  (1 Row(s) affected)

  */