constant_time_is_zero
return (unsigned char)(constant_time_is_zero(a));
return constant_time_is_zero(a ^ b);
static inline unsigned int constant_time_is_zero(unsigned int a);
mask = ~constant_time_is_zero(flen);
good = constant_time_is_zero(em[0]);
good &= constant_time_is_zero(timingsafe_memcmp(db, phash, mdlen));
unsigned int equals0 = constant_time_is_zero(db[i]);