arithmetic-operations-for/naturals-big-endian

import assert from 'assert';

import THRESHOLD_MUL_TOOM22 from '../../thresholds/THRESHOLD_MUL_TOOM22.js';

import _karatsuba from './_karatsuba.js';
import _mul_limb from './_mul_limb.js';
import _schoolbook_mul from './_schoolbook_mul.js';

/**
 * Computes C = A+B.
 *
 * Constraints:
 *   - C is zero initialized,
 *   - |A| >= |B| >= 0,
 *   - |C| >= |A| + |B|.
 *
 * TODO:
 *   - Use schoolbook mul if n = O(log m).
 *
 * @param {Number} r base (radix)
 * @param {Array} a first operand
 * @param {Number} ai a left
 * @param {Number} aj a right
 * @param {Array} b second operand, cannot have more limbs than A
 * @param {Number} bi b left
 * @param {Number} bj b right
 * @param {Array} c result, must be 0 initialized and be able to contain A+B
 * @param {Number} ci c left
 * @param {Number} cj c right
 */
export default function _mul(r, a, ai, aj, b, bi, bj, c, ci, cj) {
    assert(r >= 2);
    assert(ai >= 0 && aj <= a.length);
    assert(bi >= 0 && bj <= b.length);
    assert(ci >= 0 && cj <= c.length);
    assert(bj - bi >= 0);
    assert(aj - ai >= bj - bi);
    assert(cj - ci >= aj - ai + (bj - bi));
    assert(THRESHOLD_MUL_TOOM22 >= 1);

    // Const m = aj - ai ;
    const n = bj - bi;

    // TODO then |B| = 1 and could be faster
    // if ( m === 1 ) return _mul_limb( r , a[ai] , b , bi , bj , c , ci , cj ) ;

    if (n === 1) return _mul_limb(r, b[bi], a, ai, aj, c, ci, cj);

    // If ( m === n ) {

    // if ( a === b && ai === bi ) return _sqr( r , a , ai , aj , c , ci , cj ) ;

    // return _mul_n( r , a , ai , aj , b , bi , bj , c , ci , cj ) ;

    // }

    if (n < THRESHOLD_MUL_TOOM22) {
        return _schoolbook_mul(r, a, ai, aj, b, bi, bj, c, ci, cj);
    }

    return _karatsuba(r, a, ai, aj, b, bi, bj, c, ci, cj);
}