MASK_OFS
v = mask->bits[MASK_OFS(val)] & MASK_BIT(val);
mask->bits[MASK_OFS(val)] = v;
return mask->bits[MASK_OFS(val)] & MASK_BIT(val);
mask->bits[MASK_OFS(val)] |= MASK_BIT(val);
mask->bits[MASK_OFS(val)] &= ~MASK_BIT(val);
mask->bits[MASK_OFS(i)] |= MASK_BIT(i);
mask->bits[MASK_OFS(i)] &= ~MASK_BIT(i);