1. Let $f(x)$ be a function defined on $\mathbf{R}$, for any real number $x$ we have $f(x+3) f(x-4)=-1$. When $0 \leqslant x<7$, $f(x)=\log _{2}(9-x)$. Then the value of $f(-100)$ is $\qquad$
$-1 .-\frac{1}{2}$.
It is easy to know,
$$
\begin{array}{l}
f(x+14)=-\frac{1}{f(x+7)}=f(x) \\
\Rightarrow f(-100)=f(-100+14 \times 7) \\
\quad=f(-2)=-\frac{1}{f(5)}=-\frac{1}{\log _{2} 4}=-\frac{1}{2} .
\end{array}
$$