c_2
p_b = SCALE_MUL((int64_t)fs->c_1, (int64_t)q->avg) - fs->c_2;
u_int c_2 ; /* max_p*min_th/(max_th-min_th) (scaled) */
fs->c_2 = SCALE_MUL(fs->c_1, SCALE(fs->fs.min_th));