(PHP 5 >= 5.3.0, PHP 7)
gmp_testbit — Tests if a bit is set
a可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。
indexThe bit to test
Returns TRUE if the bit is set in resource $a,
otherwise FALSE.
An E_WARNING level error is issued when
index is less than zero, and FALSE
is returned.
Example #1 gmp_testbit() example
<?php
$n = gmp_init("1000000");
var_dump(gmp_testbit($n, 1));
gmp_setbit($n, 1);
var_dump(gmp_testbit($n, 1));
?>
以上例程会输出：
bool(false) bool(true)