Add bswap method for complex numbers. (JuliaLang#21346)

It byte-swaps the real and imaginary parts individually, following
what Fortran compilers do.

The tests read the binary test data from an ad-hoc IOBuffer,
because reinterpret doesn't work for complex numbers.

base/complex.jl

@@ -167,6 +167,9 @@ function write(s::IO, z::Complex)
  write(s,real(z),imag(z))
 end
 
+## byte order swaps: real and imaginary part are swapped individually
+bswap(z::Complex) = Complex(bswap(real(z)), bswap(imag(z)))
+
 ## equality and hashing of complex numbers ##
 
 ==(z::Complex, w::Complex) = (real(z) == real(w)) & (imag(z) == imag(w))

test/numbers.jl

@@ -2491,6 +2491,13 @@ end
 @test reinterpret(Float32,bswap(0x0000c03f)) === 1.5f0
 @test bswap(reinterpret(Float64,0x000000000000f03f)) === 1.0
 @test bswap(reinterpret(Float32,0x0000c03f)) === 1.5f0
+zbuf = IOBuffer([0xbf, 0xc0, 0x00, 0x00, 0x40, 0x20, 0x00, 0x00,
+ 0x40, 0x0c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+ 0xc0, 0x12, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])
+z1 = read(zbuf, Complex64)
+z2 = read(zbuf, Complex128)
+@test bswap(z1) === -1.5f0 + 2.5f0im
+@test bswap(z2) === 3.5 - 4.5im
 
 #isreal(x::Real) = true
 for x in [1.23, 7, e, 4//5] #[FP, Int, Irrational, Rat]