It really depends on the complexity of what you're doing. Since n cycles per 32 bit value takes n seconds on a single core, brute forcing the fast invsqrt const

It really depends on the complexity of what you're doing. Since n cycles per 32 bit value takes n seconds on a single core, brute forcing the fast invsqrt const will be done while you take a few sips of coffee. But any kind of substantial operation like building data structures and spilling to main memory can trivially leave you with a program that takes weeks.