BitUtils.jl

BitUtils.jl provides convenience functions for extracting and manipulating single bits of integer variables. The LSB is bit nr 0. For completeness also bitvectors are supported. In this case bit nr 0 is the last bit, indexed by ...[end]. I.e., after applying functions of BitUtils.jl, bitstring(a) returns the same string regardless whether a is an integer variable or a bitvector.

All functionality of BitUtils.jl can be achieved with the <<shift left and other bitwise operators in Base. But by using functions code can be clearer and more readable. For comparison, MATLAB has bitset to set a bit at a specific location.

The functions are:

• setbit(b, T=UInt) returns a value of type T where bit nr b is set, all other bits are zero. Equivalent to T(1) << 3 and T(2)^b:

  setbit(3) --> 0x0000000000000008
  setbit(3, Int8) --> 8

• setbit(x, b) returns a copy of x, but where bit nr b is set. All other bits are untouched:

  bitstring(setbit(UInt8(3), 4)) --> "00010011"

• setbit!(x, b) sets bit nr b of the bitvector x or the dereferenced x:

  x=Ref(3) --> Base.RefValue{Int64}(3)
  setbit!(x, 4) --> 19
  x[] --> 19

  Note that

  y=3;
  setbit!(Ref(y), 4) --> 19

  does not change the value of variable y (more precisely, neither the value to which y is bound, nor the binding of y):

  y   --> 3

  Generally, Julia functions cannot change the values of scalar variables (except references).

• bitset(x, b) returns true if bit nr b of x is set, otherwise false.

• setbits(b...), setbits(::Type{T}, b...), setbits(b, ::Type{T}=UInt) all return a value of type T (default UInt) where bits nr b... or collection b are set (and other bits are zero). For bitvectors use setbits!

• setbits!(x, b...), setbits!(x, b) sets the bits nr b... in x.

• anybit(x, b), anybit(x, b...) return true if in x any of the bits nr b... is set, otherwise false.