EXT_FRAC_BITS
#define fp_ext_toint(X) ((X) >> EXT_FRAC_BITS)
#define int_ext_tofp(X) ((int64_t)(X) << EXT_FRAC_BITS)
return (x * y) >> EXT_FRAC_BITS;
return div64_u64(x << EXT_FRAC_BITS, y);