function powmod($base, $exponent, $modulus)
{
if (function_exists('gmp_powm')) {
// fast
return gmp_strval(gmp_powm($base, $exponent, $modulus));
}
if (function_exists('bi_powmod')) {
// not tested
return bi_sto_str(bi_powmod($base, $exponent, $modulus));
}
if (function_exists('bcpowmod')) {
// slow
return bcpowmod($base, $exponent, $modulus);
}
// emulation, slow
$square = bcmod($base, $modulus);
$result = 1;
while (bccomp($exponent, 0) > 0) {
if (bcmod($exponent, 2)) {
$result = bcmod(bcmul($result, $square), $modulus);
}
$square = bcmod(bcmul($square, $square), $modulus);
$exponent = bcdiv($exponent, 2);
}
return $result;
}
function powm($base, $exponent, $modulus)
{
if (function_exists('gmp_powm')) {
return gmp_strval(gmp_powm($base, $exponent, $modulus));
} else {
if (function_exists('bi_powmod')) {
return bi_sto_str(bi_powmod($base, $exponent, $modulus));
} else {
if (function_exists('bcpowmod')) {
return bcpowmod($base, $exponent, $modulus);
} else {
if (preg_match("/^\\d+,\\d+,\\d+\$/", "{$base},{$exponent},{$modulus}")) {
//@FIX: this is insecure - a bi-directional proc_open() is required
if (is_executable("/usr/bin/python")) {
$r = trim(`python -c "print pow({$base}, {$exponent}, {$modulus})"`);
} else {
$r = trim(`perl -e "use Math::BigInt; print Math::BigInt->new('{$base}')->bmodpow('{$exponent}', '{$modulus}')->bstr();"`);
}
if (preg_match("/^\\d+\$/", $r)) {
return $r;
}
}
}
}
}
trigger_error("powmod: unsupported or non-integer argument", E_USER_ERROR);
}
