factorialBig function
Computes the factorial of an integer.
Implementation
BigInt factorialBig(BigInt x) {
if (x < BigInt.zero) {
throw ArgumentError.value(x, 'x', messages.argumentPositive);
}
if (x == BigInt.zero) {
return BigInt.one;
}
BigInt r = x;
while ((x -= BigInt.one) > BigInt.one) {
r *= x;
}
return r;
}