XXXI. GMP functions

These functions allow you to work with arbitrary-length integers using the GNU MP library. In order to have these functions available, you must compile PHP with GMP support by using the --with-gmp option.

You can download the GMP library from This site also has the GMP manual available.

You will need GMP version 2 or better to use these functions. Some functions may require more recent version of the GMP library.

These functions have been added in PHP 4.0.4.

Note: Most GMP functions accept GMP number arguments, defined as resource below. However, most of these functions will also accept numeric and string arguments, given that it is possible to convert the latter to a number. Also, if there is a faster function that can operate on integer arguments, it would be used instead of the slower function when the supplied arguments are integers. This is done transparently, so the bottom line is that you can use integers in every function that expects GMP number. See also the gmp_init() function.


If you want to explicitely specify a large integer, specify it as a string. If you don't do that, PHP will interpret the integer-literal first, possibly resulting in loss of precision, even before GMP comes into play.

Example 1. Factorial function using GMP

function fact ($x) {
    if ($x <= 1) 
        return 1;
        return gmp_mul ($x, fact ($x-1));

print gmp_strval (fact (1000)) . "\n";

This will calculate factiorial of 1000 (pretty big number) very fast.

Table of Contents
gmp_init -- Create GMP number
gmp_intval -- Convert GMP number to integer
gmp_strval -- Convert GMP number to string
gmp_add -- Add numbers
gmp_sub -- Subtract numbers
gmp_mul -- Multiply numbers
gmp_div_q -- Divide numbers
gmp_div_r -- Remainder of the division of numbers
gmp_div_qr -- Divide numbers and get quotient and remainder
gmp_div -- Divide numbers
gmp_mod -- Modulo operation
gmp_divexact -- Exact division of numbers
gmp_cmp -- Compare numbers
gmp_neg -- Negate number
gmp_abs -- Absolute value
gmp_sign -- Sign of number
gmp_fact -- Factorial
gmp_sqrt -- Square root
gmp_sqrtrm -- Square root with remainder
gmp_perfect_square -- Perfect square check
gmp_pow -- Raise number into power
gmp_powm -- Raise number into power with modulo
gmp_prob_prime -- Check if number is "probably prime"
gmp_gcd -- Calculate GCD
gmp_gcdext -- Calculate GCD and multipliers
gmp_invert -- Inverse by modulo
gmp_legendre -- Legendre symbol
gmp_jacobi -- Jacobi symbol
gmp_random -- Random number
gmp_and -- Logical AND
gmp_or -- Logical OR
gmp_xor -- Logical XOR
gmp_setbit -- Set bit
gmp_clrbit -- Clear bit
gmp_scan0 -- Scan for 0
gmp_scan1 -- Scan for 1
gmp_popcount -- Population count
gmp_hamdist -- Hamming distance