@technobuddha/library/modulo/modulo.ts

A large library of useful functions

/**
 * The % operator in JavaScript returns the remainder of a / b, but differs from
 * some other languages in that the result will have the same sign as the
 * dividend. For example, -1 % 8 == -1, whereas in some other languages
 * (such as Python) the result would be 7. This function emulates the more
 * correct modulo behavior, which is useful for certain applications such as
 * calculating an offset index in a circular list.
 *
 * @param a The dividend.
 * @param b The divisor.
 * @returns a % b where the result is between 0 and b (either 0 <= x < b
 * or b < x <= 0, depending on the sign of b).
 */
export function modulo(dividend: number, divisor: number): number {
    const remainder = dividend % divisor;
    return (dividend * divisor < 0 && remainder !== 0) ? divisor + remainder : remainder;
}

export default modulo;