Compare a 32 bit float and a 32 bit integer without casting to double, when either value could be too large to fit the other type exactly

Question

I have a 32 bit floating point f number (known to be positive) that I need to convert to 32 bit unsigned integer. It\'s magnitude might be too large to fit. Fur

Answer 1

I think your best bet is to be a bit platform specific. 2³² can be represented precisely in floating point. Check if f is too large to fit at all, and then convert to unsigned and check against m.

const float unsigned_limit = 4294967296.0f;
bool ok = false;
if (f < unsigned_limit)
{
    const auto uf = static_cast<unsigned int>(f);
    if (uf <= m)
    {
        ok = true;
    }
}

Not fond of the double comparison, but it's clear.

If f is usually significantly less than m (or usually significantly greater), one can test against float(m)*0.99f (respectively float(m)*1.01f), and then do the exact comparison in the unusual case. That is probably only worth doing if profiling shows that the performance gain is worth the extra complexity.