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/**
 * 有符号整型数据转换成二进制形式.
 *
 * @param int $si 要转换的整型数据
 * @param int $bits 计算机CPU位宽
 * @return string
 */
function si2bin($si, $bits=32) {
	//检查数据大小是否在范围内.
    if ($si >= -pow(2,$bits-1) and $si <= pow(2,$bits-1) ){
        if ($si < 0) {
            $si = -$si-pow(2,$bits);
        }
        $bin = base_convert($si,10,2);
        $bin_length = strlen($bin);
        if ($bin_length < $bits) $bin = str_repeat ( "0", $bits-$bin_length).$bin;
        return $bin;
    }
    return '';
}

/**
 * 二进制数据转换成有符号整数.
 *
 * @param string $bin 二进制数据
 * @param int $bits 计算机CPU位宽
 * @return int
 */
function bin2si($bin,$bits=32) {
    if (strlen($bin)==$bits) {
    	$si = base_convert($bin,2,10);
        if (substr($bin,0,1) == 1) { //负数
            $si = -(pow(2,$bits)-$si);
        }
        return $si;
    }
    return 0;
}