Let $f(x_1,\dots,x_n) = \sum_{1 \le i \le j \le n} c_{i,j}x_ix_j$ be a homogeneous quadratic form. Is there a quick-ish way to determine whether $f(x_1,\dots,x_n) \ge 0$ for all $x_1,\dots,x_n \ge 0$? 

I know how to do it in $2^n$ time, since $f$ has at most $2^n$ local minima on the set $\{(x_1,\dots,x_n) \in \mathbb{R}^n : x_1+\dots+x_n = 1, x_1,\dots,x_n \ge 0\}$ (choose a certain subset of the variables to be $0$, and then we get a bunch linear equations, from looking at derivatives, that determine the rest). But I'm wondering if there's a quicker way, in general.