Given a negative discriminant D congruent to 1 modulo 8,
returns the Weber class polynomial, defined as the minimal polynomial
of f(τ), where Z[τ] is an imaginary quadratic order of
discriminant D and f is a particular normalized Weber function
generating the same class field as j(τ). A root f(τ) of
the Weber class polynomial is an integral unit generating the ring
class field related to the corresponding root j(τ) of the
Hilbert class polynomial by the expression
j(τ) = ((f(τ)24 - 16)3 /f(τ)24),
where ( GCD)(D, 3) = 1, and
j(τ) = ((f(τ)8 - 16)3 /f(τ)8),
if 3 divides D. For further details, consult Yui and
Zagier [YZ97].
