5
ctanh (+0 + i*0) = +0 + i*0
6
ctanh (x + i*inf) = nan + i*nan for finite x
7
ctanh (x + i*nan) = nan + i*nan for finite x
8
ctanh (+inf + i*y) = 1 + i*0*sin(2y) for positive-signed finite y
9
ctanh (+inf + i*inf) = 1 +/- i*0 (unspecified sign of zero for C99)
10
ctanh (+inf + i*nan) = 1 +/- i*0 (unspecified sign of zero for C99)
11
ctanh (nan + i*0) = nan + i*0
12
ctanh (nan + i*y) = nan + i*nan for all nonzero y
13
ctanh (nan + i*nan) = nan + i*nan