I discovered that the gmp functions use [0-9a-f] up to base 16, but [0-9A-Za-z] (i.e. upper case first) from bases 17 to 62. This differs from most of the base-62 implementations I've found that tend to use lower case first.
(PHP 4 >= 4.0.4, PHP 5, PHP 7)
gmp_init — Create GMP number
Creates a GMP number from an integer or string.
numberAn integer or a string. The string representation can be decimal, hexadecimal or octal.
baseThe base.
The base may vary from 2 to 36. If base is 0 (default value), the actual base is determined from the leading characters: if the first two characters are 0x or 0X, hexadecimal is assumed, otherwise if the first character is "0", octal is assumed, otherwise decimal is assumed.
| Version | Description |
|---|---|
| 5.3.2 |
The base was extended from 2 to 36, to
2 to 62 and -2 to -36.
|
Note:
To use the extended base introduced in PHP 5.3.2, then PHP must be compiled against GMP 4.2.0 or greater.
Example #1 Creating GMP number
<?php
$a = gmp_init(123456);
$b = gmp_init("0xFFFFDEBACDFEDF7200");
?>
Note:
It is not necessary to call this function in order to use integers or strings in place of GMP numbers in GMP functions (such as with gmp_add()). Function arguments are automatically converted to GMP numbers, if such conversion is possible and needed, using the same rules as gmp_init().
I discovered that the gmp functions use [0-9a-f] up to base 16, but [0-9A-Za-z] (i.e. upper case first) from bases 17 to 62. This differs from most of the base-62 implementations I've found that tend to use lower case first.
Note: Leading zeros will make gmp_init parse this as octal.
Thus gmp_init(010) becomes 8.
$a=010; //8
$b="010" + 0; //10
$c=gmp_strval(gmp_init(010)); //8
$d=gmp_strval(gmp_init("010")); //8
This behaviour is inconsistent: either $d should equal $b, or
$b should equal $a.
Here's a way to parse a decimal (eg 3.25) into an integer and exponent:
<?
if (preg_match("/^[0-9]+\.[0-9]+$/",$input)){
//Input is a base-10 decimal. Multiply as necessary to remove the decimal
//point. Convert that to a gmp_resource, then decrement the exponent
//to compensate.
$pieces=explode(".", $input); //Split at the d.p.
$input="$pieces[0]$pieces[1]"; //Remove the decimal point.
$input=ltrim($input,'0');
//Remove any leading zeros, or gmp_init will parse the number as octal.
if ($input==''){ //Deal with "0.0" which would otherwise be ''.
$input=0;
}
$integer=gmp_init($input);
$ns_exponent=-strlen($pieces[1]);
//exponent = (-) the number of characters after the decimal point.
}
?>
Unless the base is 16, gpm_init will fail if the string begins with "0b".
> php -r '$v = gmp_init("b83", 17); print("$v\n");'
Resource id #4
> php -r '$v = gmp_init("0b83", 17); print("$v\n");'
[nothing prints]
In may case, where I am explicitly specifying the base, the solution is to apply ltrim first:
> php -r '$v = gmp_init(ltrim("0b83", "0"), 17); print("$v\n");'
Resource id #4
gmp_* functions don't accept strings with a leading '+':
<?php
echo gmp_strval(gmp_init('+42')); #0
echo gmp_strval(gmp_add('42', '+42')); #42
echo bcadd('+42', '+42'); #84
?>
If you call a gmp_* function directly with an interger as parameter, this integer MUST NOT be 0:
for($i=-1;$i<=1;$i++) { echo gmp_strval(gmp_add(2,gmp_mul(1,$i))) . ' '; }
The result is 1 0 3 (wrong)
In this case you have to use gmp_init():
for($i=-1;$i<=1;$i++) { echo gmp_strval(gmp_add(2,gmp_mul(1,gmp_init($i)))) . ' '; }
The result is 1 2 3 (right)
Happy number crunching! :-)