Enumerator::ArithmeticSequence#last

static VALUE
arith_seq_last(int argc, VALUE *argv, VALUE self)
{
    VALUE b, e, s, len_1, len, last, nv, ary;
    int last_is_adjusted;
    long n;

    e = arith_seq_end(self);
    if (NIL_P(e)) {
        rb_raise(rb_eRangeError,
                 "cannot get the last element of endless arithmetic sequence");
    }

    b = arith_seq_begin(self);
    s = arith_seq_step(self);

    len_1 = num_idiv(num_minus(e, b), s);
    if (rb_num_negative_int_p(len_1)) {
        if (argc == 0) {
            return Qnil;
        }
        return rb_ary_new_capa(0);
    }

    last = num_plus(b, num_mul(s, len_1));
    if ((last_is_adjusted = arith_seq_exclude_end_p(self) && rb_equal(last, e))) {
        last = num_minus(last, s);
    }

    if (argc == 0) {
        return last;
    }

    if (last_is_adjusted) {
        len = len_1;
    }
    else {
        len = rb_int_plus(len_1, INT2FIX(1));
    }

    rb_scan_args(argc, argv, "1", &nv);
    if (!RB_INTEGER_TYPE_P(nv)) {
        nv = rb_to_int(nv);
    }
    if (RTEST(rb_int_gt(nv, len))) {
        nv = len;
    }
    n = NUM2LONG(nv);
    if (n < 0) {
        rb_raise(rb_eArgError, "negative array size");
    }

    ary = rb_ary_new_capa(n);
    b = rb_int_minus(last, rb_int_mul(s, nv));
    while (n) {
        b = rb_int_plus(b, s);
        rb_ary_push(ary, b);
        --n;
    }

    return ary;
}