Largest representable negative floating-point number

Question

What is a platform-independent way of specifying the largest representable negative floating-point number?

We found an algorithm that broke when run on a PS3's SPU, but worked fine when compiled for the PPU:

float x = -FLT_MAX;
/* stuff */
if (x > 0.0f) {
    // If x is unchanged, code is executed on SPU
}

Essentially, is there a well-defined negative equivalent of FLT_MAX?

Answer 1

You want std::numeric_limits::lowest(), but it is c++0x only, so not very cross platform at the moment.

You definitely don't want std::numeric_limits::min() - that is smallest magnitude, not furthest negative.

If you want something that will always be less than all other doubles, use -numeric_limits<double>::infinity().