Ln

    // Testing: https://ideone.com/u0IkCn
    define float LogError = 0.00000005f;

    public static float Log(float value)
    {
        float nom = (value - 1.0f) / (value + 1.0f);
        float dnm = 1.0f;
        float p = nom * nom;
        float a = nom;
        float log = a;
        while (true) {
            nom = nom * p;
            dnm = dnm + 2.0f;
            float an = nom / dnm;
            log = log + an;
            float delta = an - a;
            if (delta < 0) delta = -delta;
            if (delta <= LogError)
                break;
            a = an;
        }
        return 2.0f * log;
    }