add bitrotate (#42)

src/BitIntegers.jl

@@ -3,6 +3,7 @@
 module BitIntegers
 
 import Base: &, *, +, -, <, <<, <=, ==, >>, >>>, |, ~, AbstractFloat, add_with_overflow,
+             bitrotate,
              bitstring, bswap, checked_abs, count_ones, div, flipsign, isodd, leading_zeros,
              mod, mul_with_overflow, ndigits0zpb, peek, promote_rule, read, rem, signed,
              sub_with_overflow, trailing_zeros, typemax, typemin, unsigned, write, xor
@@ -358,6 +359,12 @@ end
 @inline <<( x::UBI, y::Int) = 0 <= y ? x << unsigned(y) :  x >> unsigned(-y)
 @inline >>>(x::UBI, y::Int) = 0 <= y ? x >>> unsigned(y) : x << unsigned(-y)
 
+function bitrotate(x::T, k::Integer) where {T<:XBI}
+    l = (sizeof(T) << 3) % UInt
+    k::UInt = mod(k, l)
+    (x << k) | (x >>> (l-k))
+end
+
 count_ones(    x::XBI) = Int(ctpop_int(x))
 leading_zeros( x::XBI) = Int(ctlz_int(x))
 trailing_zeros(x::XBI) = Int(cttz_int(x))

test/runtests.jl

@@ -257,6 +257,22 @@ end
 end
 
 
+@testset "bit rotations" begin
+    for X in XInts
+        x = X(24)
+        l = 8*sizeof(X)
+        @test bitrotate(x, 2) == 4*x
+        @test bitrotate(x, l-1) == div(x, 2)
+        x = rand(X)
+        for k in (0, UInt8(13), UInt32(371), Int16(-123), Int64(-1072), BigInt(-21330))
+            y = @inferred bitrotate(x, k)
+            @test y isa X && bitrotate(y, k) == bitrotate(x, 2*k)
+            k isa Signed && @test bitrotate(y, -k) == x
+        end
+    end
+end
+
+
 @testset "arithmetic operations" begin
     for (X, Y) in TypeCombos
         T = promote_type(X, Y)