aureooms/js-integer-little-endian

/**
 * Computes pow(a, b) using exponentiation by squaring.
 *
 * *could add an additional base case for b = 1*
 *
 */

export function __ebs__ (alloc, iszero, setone, iseven, div2, minus1) {

    var ebs = function (a, ai, aj, b, bi, bj, c, ci, cj) {

        var t, u, m, n;

        if ( iszero(b, bi, bj) ) {
            setone(c, ci, cj);
        }
        else if ( iseven(b, bi, bj) ) {
            m = bj - bi;
            t = alloc(m);
            t = div2(b, bi, bj, t, 0, m);

            n = cj - ci;
            u = alloc(n);

            ebs(a, ai, aj, t, 0, m, u, 0, n);

            mul(u, 0, n, u, 0, n, c, ci, cj);
        }
        else{
            m = bj - bi;
            t = alloc(m);
            t = minus1(b, bi, bj, t, 0, m);

            n = cj - ci;
            u = alloc(n);

            ebs(a, ai, aj, t, 0, m, u, 0, n);

            mul(a, ai, aj, u, 0, n, c, ci, cj);
        }
    };
}