/* Extracts an integer clear operation (subset) from the given linear op. */
static av_noinline bool extract_constant_rows(SwsLinearOp *c, SwsComps prev,
                                              SwsConst *out_clear)
{
    SwsConst clear = {0};
    bool ret = false;

    for (int i = 0; i < 4; i++) {
        bool const_row = c->m[i][4].den == 1; /* offset is integer */
        for (int j = 0; j < 4; j++) {
            const_row &= c->m[i][j].num == 0 || /* scalar is zero */
                         (prev.flags[j] & SWS_COMP_ZERO); /* input is zero */
        }
        if (const_row && (c->mask & SWS_MASK_ROW(i))) {
            clear.q4[i] = c->m[i][4];
            for (int j = 0; j < 5; j++)
                c->m[i][j] = Q(i == j);
            c->mask &= ~SWS_MASK_ROW(i);
            ret = true;
        }
    }

    if (ret)
        *out_clear = clear;
    return ret;
}