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

The first long to be 'wrong' when cast to a double will not be off by 1e-8, it will be off by 1. As long as the double can fit the long in its significand, it will represent it accurately.

I forget exactly how many bits a double has for precision vs offset, but that would tell you the max size it could represent. The first long to be wrong should have the binary form 10000..., so you can find it much quicker by starting at 1 and left-shifting.

Wikipedia says 52 bits in the significand, not counting the implicit starting 1. That should mean the first long to be cast to a different value is 2^53.