aureooms/js-integer-big-endian

import assert from 'assert';

import _cmp_half from '../../compare/_cmp_half.js';
import _cmp_n from '../../compare/_cmp_n.js';
import _isub from '../sub/_isub.js';

import _imod_schoolbook_subroutine_do from './_imod_schoolbook_subroutine_do.js';

/**
 * Input
 * -----
 *  - Two integers A and B such that 0 <= A < β^(n+1) and (β^n)/2 <= B < β^n.
 *  - |A| = |B| + 1
 *
 * Output
 * -----
 *  The remainder A mod B.
 *
 * @param {Number} r The radix.
 * @param {Array} a Dividend.
 * @param {Number} ai Left of dividend.
 * @param {Number} aj Right of dividend.
 * @param {Array} b Divisor.
 * @param {Number} bi Left of divisor.
 * @param {Number} bj Right of divisor.
 */
export default function _imod_schoolbook_subroutine(r, a, ai, aj, b, bi, bj) {
    assert(r >= 2);
    assert(ai >= 0 && aj <= a.length);
    assert(bi >= 0 && bj <= b.length);
    assert(aj - ai === bj - bi + 1); // |A| = |B| + 1
    assert(_cmp_half(r, b, bi, bj) >= 0); // (β^n)/2 <= B < β^n

    // If A ≥ B*β, compute the remainder r of ( A − B*β ) / B
    // and return it.
    // Note that then A − B*β < B*β since A < 2 B*β because of the
    // preconditions above. Hence the preconditions hold for
    // _imod_schoolbook_subroutine_do.
    if (_cmp_n(a, ai, aj - 1, b, bi) >= 0) {
        _isub(r, a, ai, aj - 1, b, bi, bj);
    }

    _imod_schoolbook_subroutine_do(r, a, ai, aj, b, bi, bj);
}