What's the first double that deviates from its corresponding long by delta?

Question

I want to know the first double from 0d upwards that deviates by the long of the \"same value\" by some delta, say 1e-8. I\'m failing here though. I\'m trying to do this i

Answer 1

Although I'm hesitant to mention Fortran 95 and successors in this discussion, I'll mention that Fortran since the 1990 standard has offered a SPACING intrinsic function which tells you what the difference between representable REALs are about a given REAL. You could do a binary search on this, stopping when SPACING(X) > DELTA. For compilers that use the same floating point model as the one you are interested in (likely to be the IEEE754 standard), you should get the same results.