The function GIquadres returns $1$ if a is a quadratic residue $\mathbf{mod}b$, and $\mathrm{-1}$ if a is a quadratic non-residue $\mathbf{mod}b$.

The number a is a quadratic residue of b where a and b are coprime if a has a square root $\mathbf{mod}b$, that is, there exists a Gaussian integer c such that $c^2$ is congruent to $a\mathbf{mod}b$.

$\mathrm{with}\left(\mathrm{GaussInt}\right)\:$

$\mathrm{GIquadres}\left(-1\,3+7\mathrm{I}\right)$

$1$

$\mathrm{GIquadres}\left(47364374-48434834\mathrm{I}\,84734834-3434347\mathrm{I}\right)$

$\mathrm{-1}$