<?php
function base62encode($data) {
$outstring = '';
$l = strlen($data);
for ($i = 0; $i < $l; $i += 8) {
$chunk = substr($data, $i, 8);
$outlen = ceil((strlen($chunk) * 8)/6); //8bit/char in, 6bits/char out, round up
$x = bin2hex($chunk); //gmp won't convert from binary, so go via hex
$w = gmp_strval(gmp_init(ltrim($x, '0'), 16), 62); //gmp doesn't like leading 0s
$pad = str_pad($w, $outlen, '0', STR_PAD_LEFT);
$outstring .= $pad;
}
return $outstring;
}
/**
* Decode base-62 encoded text into binary
* Note that because base-62 encodes slightly less than 6 bits per character (actually 5.95419631038688), there is some wastage
* In order to make this practical, we chunk in groups of up to 11 input chars, which give up to 8 output chars
* with a wastage of up to 4 bits per chunk, so while the output is not quite as space efficient as a
* true multiprecision conversion, it's orders of magnitude faster
* Note that the input of this function is not compatible with that of a multiprecision conversion, but it's a practical encoding implementation
* The encoding overhead tends towards 37.5% with this chunk size; bigger chunk sizes can be slightly more space efficient, but may be slower
* Base-64 doesn't suffer this problem because it fits into exactly 6 bits, so it generates the same results as a multiprecision conversion
* Requires PHP 5.3.2 and gmp 4.2.0
* @param string $data Base-62 encoded text (not chunked or split)
* @return string Decoded binary data
*/
function base62decode($data) {
$outstring = '';
$l = strlen($data);
for ($i = 0; $i < $l; $i += 11) {
$chunk = substr($data, $i, 11);
$outlen = floor((strlen($chunk) * 6)/8); //6bit/char in, 8bits/char out, round down
$y = gmp_strval(gmp_init(ltrim($chunk, '0'), 62), 16); //gmp doesn't like leading 0s
$pad = str_pad($y, $outlen * 2, '0', STR_PAD_LEFT); //double output length as as we're going via hex (4bits/char)
$outstring .= pack('H*', $pad); //same as hex2bin
}
return $outstring;
}
$data = "?1,2,3,45,4536,1234567";
$encode = base62encode($data);
echo 'Encode: '.$encode;
echo ' - '.base62decode($encode);
Fatal error: Uncaught Error: Call to undefined function gmp_strval() in /in/MtBjQ:10
Stack trace:
#0 /in/MtBjQ(43): base62encode('?1,2,3,45,4536,...')
#1 {main}
thrown in /in/MtBjQ on line 10
Process exited with code 255.
Output for 5.5.35, 5.6.21
Fatal error: Call to undefined function gmp_strval() in /in/MtBjQ on line 10
Process exited with code 255.