/**
* Generate a random number
*
* @param optional Integer $min
* @param optional Integer $max
* @return BigInteger
* @access public
*/
function random($min = false, $max = false)
{
if ($min === false) {
$min = new BigInteger(0);
}
if ($max === false) {
$max = new BigInteger(0x7fffffff);
}
$compare = $max->compare($min);
if (!$compare) {
return $this->_normalize($min);
} else {
if ($compare < 0) {
// if $min is bigger then $max, swap $min and $max
$temp = $max;
$max = $min;
$min = $temp;
}
}
static $one;
if (!isset($one)) {
$one = new BigInteger(1);
}
$max = $max->subtract($min->subtract($one));
$size = strlen(ltrim($max->toBytes(), chr(0)));
/*
doing $random % $max doesn't work because some numbers will be more likely to occur than others.
eg. if $max is 140 and $random's max is 255 then that'd mean both $random = 5 and $random = 145
would produce 5 whereas the only value of random that could produce 139 would be 139. ie.
not all numbers would be equally likely. some would be more likely than others.
creating a whole new random number until you find one that is within the range doesn't work
because, for sufficiently small ranges, the likelihood that you'd get a number within that range
would be pretty small. eg. with $random's max being 255 and if your $max being 1 the probability
would be pretty high that $random would be greater than $max.
phpseclib works around this using the technique described here:
http://crypto.stackexchange.com/questions/5708/creating-a-small-number-from-a-cryptographically-secure-random-string
*/
$random_max = new BigInteger(chr(1) . str_repeat("", $size), 256);
$random = $this->_random_number_helper($size);
list($max_multiple) = $random_max->divide($max);
$max_multiple = $max_multiple->multiply($max);
while ($random->compare($max_multiple) >= 0) {
$random = $random->subtract($max_multiple);
$random_max = $random_max->subtract($max_multiple);
$random = $random->bitwise_leftShift(8);
$random = $random->add($this->_random_number_helper(1));
$random_max = $random_max->bitwise_leftShift(8);
list($max_multiple) = $random_max->divide($max);
$max_multiple = $max_multiple->multiply($max);
}
list(, $random) = $random->divide($max);
return $this->_normalize($random->add($min));
}
/**
* Prepare a number for use in Montgomery Modular Reductions
*
* @see _montgomery()
* @see _slidingWindow()
* @access private
* @param Array $x
* @param Array $n
* @return Array
*/
function _prepMontgomery($x, $n)
{
$lhs = new BigInteger();
$lhs->value = array_merge($this->_array_repeat(0, count($n)), $x);
$rhs = new BigInteger();
$rhs->value = $n;
list(, $temp) = $lhs->divide($rhs);
return $temp->value;
}
