gmp_sqrtrem
A gotcha when using the value from gmp_strval as a key in an associative array. Some numbers are 2^31 are converted to signed integer format, this is usually incorrect.
<?php
$a = gmp_init('2147483649'); // = 2^31 + 1
$b = gmp_init('3173604585'); // = 2^31 < $b < 2^32
$c = gmp_strval($a);
$d = gmp_strval($b);
$e = array($c => 'c', $d => 'd');
print '*** Expect '."\n";
print 'Array '."\n".'('."\n".' ['.$c.'] => c'."\n".' ['.$d.'] => d'."\n".')'."\n\n";
print '*** Actual '."\n";
print_r($e);
?>
Output:
*** Expect
Array
(
[2147483649] => c
[3173604585] => d
)
*** Actual
Array
(
[-2147483647] => c
[3173604585] => d
)
A workaround is to format as base 16 and append '0x' before using as a key.
gmp_strval
(PHP 4 >= 4.0.4, PHP 5)
gmp_strval — Convert GMP number to string
Description
string gmp_strval
( resource
$gmpnumber
[, int $base = 10
] )
Convert GMP number to string representation in base
base. The default base is 10.
Parameters
-
gmpnumber -
The GMP number that will be converted to a string.
It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.
-
base -
The base of the returned number. The default base is 10. Allowed values for the base are from 2 to 62 and -2 to -36.
Return Values
The number, as a string.
Changelog
| Version | Description |
|---|---|
| 5.3.2 |
The base was extended from 2 to 36, to
2 to 62 and -2 to -36.
|
Notes
Note:
To use the extended base introduced in PHP 5.3.2, then PHP must be compiled against GMP 4.2.0 or greater.
Examples
Example #1 Converting a GMP number to a string
<?php
$a = gmp_init("0x41682179fbf5");
printf("Decimal: %s, 36-based: %s", gmp_strval($a), gmp_strval($a,36));
?>
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User Contributed Notes
gmp_strval - [3 notes]
russell dot s dot harper at gmail dot com ¶
3 years ago
php at richardneill dot org ¶
6 years ago
I think it's no longer necessary to worry about trailing nulls. This was fixed in Feb 2002 (see bug 10133)
caldwell at utm dot NoSpamPlease dot edu ¶
11 years ago
Warning: gmp_strval may return a null terminated string (e.g., gmp_strval(gmp_init(8)) has two characters. This is because gmp is built for speed, so uses estimates based on things it can get quickly, like the number of bits in N. So since 8 is a 4 bit number, it will be allocated ceil(log10(2^4))=ceil(4*0.30103....) = 2 characters. The gmp folks feel it is the caller's responsibility (in this case the PHP interface) to check whether or not all the characters were required. PHP might have done this for us (and may in the future), but for now, you need to check (if it matters to you--it sure did in my program!).