accurate and reliable Base36 in PHP? - php

Question

Here is my code so far:
function base36($value, $return_size)
{
$base36 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$buffer = str_pad("", $return_size);
$offset = $return_size;
do {
$buffer[--$offset] = $base36[$value % 36];
} while ($value /= 36);
return $buffer;
}
$value: 64bit integer
$return_size: the expected size in bytes the function should return
It doesn't work correctly, because the $value is 64bit integer and because PHP forces double divisions. PHP seems pretty limited when it's about 64bit integers. How to make the above code work like the exact C version would?

Answer 1

Native:
base_convert is a function which happens to do exactly what you want to do.
string base_convert ( string $number , int $frombase , int $tobase )
Its input structure is limited between base 2 and base 36 so it covers what you need. It is most likely (like many other PHP functions) just a light wrapper over the C library originals.
GMP:
gmp_strval is another function which happens to do exactly what you want to do -- it also has better precision (because GMP is a multiprecision arithmetic library).
GMP values need to be initialized from strings using gmp_init and the resulting value (is a resource) is used in all subsequent GMP arithmetic function calls.
It has a higher number of available bases (from 2 to 62) but it is a bit less fun to work with because of the requirement to init the values and use them as resources.
The less fun part isn't true if you're running PHP 5.6 because GMP overloads the arithmetic operators in that version allowing GMP objects (resources?) to be added substracted etc. by using the operators.
Here's a simple GMP conversion function example that doesn't require that you initialize values with gmp_init:
function gmp_convert($num, $base_a, $base_b)
{
return gmp_strval ( gmp_init($num, $base_a), $base_b );
}