ardupilot/libraries/AP_Math/AP_Math.cpp

#include "AP_Math.h"
#include <float.h>

// a varient of asin() that checks the input ranges and ensures a
// valid angle as output. If nan is given as input then zero is
// returned.
float safe_asin(float v)
{
    if (isnan(v)) {
        return 0.0f;
    }
    if (v >= 1.0f) {
        return M_PI/2;
    }
    if (v <= -1.0f) {
        return -M_PI/2;
    }
    return asinf(v);
}

// a varient of sqrt() that checks the input ranges and ensures a
// valid value as output. If a negative number is given then 0 is
// returned. The reasoning is that a negative number for sqrt() in our
// code is usually caused by small numerical rounding errors, so the
// real input should have been zero
float safe_sqrt(float v)
{
    float ret = sqrtf(v);
    if (isnan(ret)) {
        return 0;
    }
    return ret;
}