aureooms/js-integer-big-endian

import assert from 'assert';

/**
 * Compute x * b where x is a single limb.
 * 0 <= x <= r-1
 * No restriction on operand sizes.
 */

export default function _mul_limb(r, x, b, bi, bj, c, ci, cj) {
    assert(r >= 2);
    assert(x >= 0 && x <= r - 1);
    assert(bi >= 0 && bj <= b.length);
    assert(ci >= 0 && cj <= c.length);

    let C = 0;

    while (true) {
        --bj;
        --cj;

        if (bj < bi) {
            if (cj >= ci) c[cj] = C;
            return;
        }

        if (cj < ci) return;

        const t = b[bj] * x + C;

        c[cj] = t % r;

        C = (t / r) | 0;
    }
}