Can you tell me how the invert function for the following PHP function is?
<?php
function id2secure($old_number) {
$alphabet_en = '1357902468acegikmoqsuwybdfhjlnprtvxz-_';
$new_number = '';
while ($old_number > 0) {
$rest = $old_number%38;
if ($rest >= 38) { return FALSE; }
$new_number .= $alphabet_en[$rest];
$old_number = floor($old_number/38);
}
$new_number = strrev($new_number);
return $new_number;
}
echo id2secure(172293);
?>
Thank you very much in advance!
This is secure :) Took me a few minutes to crack it. Here you go,
function secure2id($new_number) {
$alphabet_en = '1357902468acegikmoqsuwybdfhjlnprtvxz';
$old_number = 0;
$new_number = strrev($new_number);
$len=strlen($new_number);
$n=0;
$base=1;
while($n<$len){
$c=$new_number[$n];
$index = strpos($alphabet_en, $c);
if ($index === false)
break;
$old_number += $base * $index;
$base *= 38;
$n++;
}
return $old_number;
}
Haven't tested this code, but it might work:
<?php function secure2id($sr)
{
$s = strrev($sr);
$alpha = '1357902468acegikmoqsuwybdfhjlnprtvxz';
$alpha2num = array();
$n = strlen($alpha);
for($i = 0; $i < $n; $i++)
{
$alpha2num[$alpha[$i]] = $i;
}
$rez = 0;
$n = strlen($s);
$b = 1;
for($i = 0; $i < $n; $i++)
{
$rez += $b * $alpha2num[$s[$i]];
$b *= 38;
}
return $rez;
} ?>
`
Are you asking how to convert base 38 to base 10? The numerical algorithm is this:
Let N be the new number in base 10. Set N to zero to start with.
Let X be the original number in base 38.
Multiply N by 38.
Let D be the most significant (leftmost) digit of X.
Let T be the value of D in base 10.
Add T to N.
Remove D from X (so the number X is now 1 digit shorter).
If X is empty, goto 10.
Goto 3.
Return N, which is now the fully converted base 10 number.
Now that you understand the math, it should be fairly straightforward to convert these steps to a PHP function.
Related
I'm using GMP library of php to solve a problem of formulary.
public function gmp_sum($aRessource)
{
// Avec le while
$i = 0;
$nb_ressource = count($aRessource);
while ($i < $nb_ressource)
{
if ($i == 0)
{
$tmp = gmp_init($aRessource[$i]);
}
else
{
$tmp = gmp_add(gmp_init($aRessource[$i]),$tmp);
}
$i++;
}
return $tmp;
}
The variable $aRessource is equal to : array(1,2,4,8);
so my function gmp_sum is returning 15.
I want to create an algorithm who does the reverse operation, the function take the integer 15 and return me an array who contains 1 2 4 8. But I do not know where to start.
Thanks for the help
Solution :
Decompose integer to power of 2 in php
public function gmp_reverse($gmp_sum)
{
$res = array();
$i = 1;
while ($i < 64) // 64 bytes
{
$tmp = $gmp_sum & $i; // check if bytes equal to 1
if ($tmp != 0)
{
array_push($res,$i);
}
$i = $i * 2;
}
return $res;
}
Assuming you want an array which adds up to the sum, you want a reverse of that. This function assumes, you have a perfect input, so for example, 17 will not work.
Try it out.
function reversegen($gmpsum)
{
$stack = array();
$limit = $gmpsum;
$cur = 1;
for($sum = 0; $sum < $limit; )
{
echo $cur. "<br>";
array_push($stack,$cur);
$sum = $sum + $cur;
$cur = 2 * $cur;
}
return($stack);
}
$stack = reversegen(15);
print_r($stack);
15 above is for representative purpose. You can use, 31, 63, 127 etc and it will still work fine.
I want to divide a number into n number of parts like follows
Input : $n = 4;$m =14;
Output should as : array(1=>4,2=>4,3=>3,4=>3);
i.e :
$n $m
1 1+1+1+1
2 1+1+1+1
3 1+1+1
4 1+1+1
Any suggestions or links would help a lot.
Here is one way to do it - this works in phpfiddle:
$n = 4;
$m =14;
$array = distribute($m,$n);
print_r($array);
function distribute($m,$n) {
$div = floor($m / $n);
$mod = fmod($m, $n);
$result = array();
for ($i = 1;$i <= $n;$i++) {
$result[$i] = $div;
}
if ($mod > 0) {
for ($i = 1;$i <= $mod;$i++) {
$result[$i] = $result[$i] + 1;
}
}
return $result;
}
I have a php script that creates a random 10 digit order number:
// Assign order number length
$digits = 10;
// Create random order number to be stored with this order
$order_number = rand(pow(10, $digits-1), pow(10, $digits)-1);
How do I prevent this from ever including the digit zero 0 in the random 10 digit number? Thanks in advance!
You can do fancy base conversions, but in the end, the most straightforward way is to just get a string:
function random_string($count, $available) {
$result = '';
$max = strlen($available) - 1;
for($i = 0; $i < $count; $i++) {
$result .= $available[rand(0, $max)];
}
return $result;
}
…
$order_number = random_string($digits, '123456789');
You can treat it as a number of base 9
base_convert(rand(0, pow(9, $digits) - 1), 10, 9)
This will give you numbers with digits from 0 to 8.
Now just add 1 to every digit to make it 1 to 9
(pow(10, $digits) - 1) / 9
will give you a number filled with ones. Now just add it to your previous number and there you go:
$digits = 10;
$order_number = (pow(10, $digits) - 1) / 9 + base_convert(rand(0, pow(9, $digits) - 1), 10, 9);
Try this :D
function getRandom($from, $to){
$num = rand($from, $to);
$have_zero = true;
$strNum = strval($num);
while ($have_zero){
$have_zero = false;
for ($i = 0; $i < sizeof($strNum); $i++){
if ($strNum[$i] == '0'){
$have_zero = true;
$num = rand($from, $to);
$strNum = strval($num);
break;
}
}
}
return $num;
}
getRandom(1111111111, 9999999999);
You could use a simple function like this:
function getRandom($length) {
$numbers = '';
for($i = 0; $i < $length; $i++) {
$numbers .= rand(1, 9);
}
return $numbers;
}
echo getRandom(10);
I would make a function.
<?php
function myRandomNumberWithoutZeros($digits)
{
$result = str_replace("0", "",rand(pow(10,$digits-1), pow(10, $digits)-1)."");
$resultLength = strlen($result);
if($resultLength < $digits)
{
return intval($result.myRandomNumberWithoutZeros($digits-$resultLength));
}
return intval($result);
}
echo myRandomNumberWithoutZeros(10);
?>
I'm trying to make something like this to my variable data value...
$maxvalue = 0;
$basevalue = 0;
if($basevalue == 0) {$maxvalue = 0;}
else if ($basevalue == 1) {$maxvalue = 884;}
else if ($basevalue == 2) {$maxvalue = 1819;}
else if ($basevalue == 3) {$maxvalue = 2839;}
and so on.. i believe there is no exact computation on how the $maxvalue shifts as the basevalue increase. Can someone suggest me a simplier way to do this? thanks in advance!
$maxvalues = array(0, 884, 1819, 2839, ...);
$maxvalue = $maxvalues[$basevalue];
It looks like there's a pattern, almost like a faculty, but also with some other calculations. All numbers are multiples of 17. The following function returns the numbers you provided, so I think it might work for the higher numbers too:
function getMaxValue($base)
{
// Factor of $base = 51 + $base^2 + Factor($base - 1). You
// could solve that in a recursion, but a loop is generally better.
$factor = 0;
for ($i = 1; $i <= $base; $i++)
$factor += 51 + ($i * $i);
return $factor * 17;
}
// Test
for ($i = 0; $i < 100; $i++)
{
echo "$i -- " . getMaxValue($i) . "<br>\n";
}
Here's the solution that prevented me putting all of them in an array..
$maxvalue = 17/6*(2*($basevalue*$basevalue*$basevalue)+3
($basevalue*$basevalue)+307*$basevalue);
Thanks for all the help
I am looking to create an auto incrementing unique string using PHP, containing [a-Z 0-9] starting at 2 chars long and growing when needed.
This is for a url shrinker so each string (or alias) will be saved in the database attached to a url.
Any insight would be greatly appreciated!
Note this solution won't produce uppercase letters.
Use base_convert() to convert to base 36, which will use [a-z0-9].
<?php
// outputs a, b, c, ..., 2o, 2p, 2q
for ($i = 10; $i < 99; ++$i)
echo base_convert($i, 10, 36), "\n";
Given the last used number, you can convert it back to an integer with intval() increment it and convert the result back to base 36 with base_convert().
<?php
$value = 'bc9z';
$value = intval($value, 36);
++$value;
$value = base_convert($value, 10, 36);
echo $value; // bca0
// or
echo $value = base_convert(intval($value, 36) + 1, 10, 36);
Here's an implementation of an incr function which takes a string containing characters [0-9a-zA-Z] and increments it, pushing a 0 onto the front if required using the 'carry-the-one' method.
<?php
function incr($num) {
$chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$parts = str_split((string)$num);
$carry = 1;
for ($i = count($parts) - 1; $i >= 0 && $carry; --$i) {
$value = strpos($chars, $parts[$i]) + 1;
if ($value >= strlen($chars)) {
$value = 0;
$carry = 1;
} else {
$carry = 0;
}
$parts[$i] = $chars[$value];
}
if ($carry)
array_unshift($parts, $chars[0]);
return implode($parts);
}
$num = '0';
for ($i = 0; $i < 1000; ++$i) {
echo $num = incr($num), "\n";
}
If your string was single case rather than mixed, and didn't contain numerics, then you could literally just increment it:
$testString="AA";
for($x = 0; $x < 65536; $x++) {
echo $testString++.'<br />';
}
$testString="aa";
for($x = 0; $x < 65536; $x++) {
echo $testString++.'<br />';
}
But you could possibly make some use of this feature even with a mixed alphanumeric string
To expand on meagar's answer, here is how you can do it with uppercase letters as well and for number arbitrarily big (requires the bcmath extension, but you could as well use gmp or the bigintegers pear package):
function base10ToBase62($number) {
static $chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
$result = "";
$n = $number;
do {
$remainder = bcmod($n, 62);
$n = bcdiv($n, 62);
$result = $chars[$remainder] . $result;
} while ($n > 0);
return $result;
}
for ($i = 10; $i < 99; ++$i) {
echo base10ToBase62((string) $i), "\n";
}