IEE 754 total order in standard C++11

Question

According to the IEEE floating point wikipage (on IEEE 754), there is a total order on double-precision floating points (i.e. on C++11 implementations having IEEE-754 floats, li

Answer 1

I would use:

int totalcompare(double x, double y) {
    int64_t rx, ry;

    memcpy(&rx, &x, sizeof rx);
    memcpy(&ry, &y, sizeof ry);

    if (rx == ry) return 0;

    if (rx < 0) rx ^= INT64_MAX;
    if (ry < 0) ry ^= INT64_MAX;

    if (rx < ry) return -1; else return 1;
 }

This makes 0.0 and -0.0 compare unequal, whereas if (x==y) return 0; in your version makes them compare equal, meaning that your version is only a preorder. NaN values are above the rest and different NaNs compare different. All values comparable for <= should be in the same order for the above relation.

Note: the above function is C. I do not know C++.