Function: qfbnucomp
Section: number_theoretical
C-Name: nucomp
Prototype: GGG
Help: qfbnucomp(x,y,L): composite of primitive positive definite quadratic
 forms x and y using nucomp and nudupl, where L=[|D/4|^(1/4)] is precomputed.
Doc: \idx{composition} of the primitive positive
 definite binary quadratic forms $x$ and $y$ (type \typ{QFB}) using the NUCOMP
 and NUDUPL algorithms of \idx{Shanks}, \`a la Atkin. $L$ is any positive
 constant, but for optimal speed, one should take $L=|D/4|^{1/4}$, i.e.
 \kbd{sqrtnint(abs(D)>>2,4)}, where $D$ is the common discriminant of $x$ and
 $y$. When $x$ and $y$ do not have the same discriminant, the result is
 undefined.

 The current implementation is slower than the generic routine for small $D$,
 and becomes faster when $D$ has about $45$ bits.

Variant: Also available is \fun{GEN}{nudupl}{GEN x, GEN L} when $x=y$.
