1. Let $f(x)$ be a function defined on $\mathbf{R}$, such that for any real number $x$, $f(x+3) \cdot f(x-4)=-1$. Also, when $0 \leqslant x<7$, $f(x)=\log _{2}(9-x)$, then the value of $f(-100)$ is $\qquad$ .