Big numbers selfmade: Part 6/14: Factorials

Here the factorial function:

/**
 * calculates the factorial of an int number.
 * This uses a simple iterative loop.
 */
public static DecimalBigInt factorial(int n) {
    DecimalBigInt fac = new DecimalBigInt(1);
    for(int i = 2; i <= n; i++) {
        fac = fac.times(new DecimalBigInt(i));
    }
    return fac;
}

This gives us

fac(90) = 1485715964481761497309522733620825737885569961284688766942216863704985393094065876545992131370884059645617234469978112000000000000000000000

We don’t really want to use a DecimalBigInt as input, as this simple implementation takes already too long for larger int values (and needs lots of memory, too).

For the original question this would be enough, but we want a more usable class. The next parts will add more useful methods.

0: introduction, 1: number representation, 2: conversion from decimal format, 3: decimal formatting, 4: addition, 5: multiplication, 6: factorials, 7: comparison, 8: normalizing, 9: equals/hashCode, 10: converting between arbitrary radix systems, 11: converting from arbitrary radix, 12: division by small numbers, 13: conversion to arbitrary radix, 14: missing bits - Original question - Full code

Tags: factorial big number Java english big-numbers-selfmade