I think it is safe, since I've never had any problems. Only comparisons may be the problem because of decimal places, but you'll never have those decimal places anyway since you are working just with integers.

There are so-called safe integers--the integers which are exactly representable in a double type. The name comes from ECMAScript, which does not even know what an integer is and always uses floating-point numbers (barring some corner cases). All integers from $$$-2^{53}$$$ to $$$2^{53}$$$ are safe, which means you can treat double just like an integral type as long as you stay within these bounds. For a 80-bit IEEE 754 type, that is, long double on *nix GCC, the range is $$$-2^{64}$$$ to $$$2^{64}$$$.

Hmm probably depends on what kind of integers and what kind of doubles we're talking about right?

Because double has gaps between very big integers and for sufficiently big integers we could probably use that.

Why would you want to do this though

nice blog