input: float v    // time value
output:   int a, b // mantissa, exponent of time code

(a, b) encode (v):

    if (v == 0)
        return (0, 0)

    if (v < 2 * C)                              // subnormal
        a = floor (v * 4 / C)                   // round down
        return (a, 0)
    else                                        // normalized
        if (v > (1 + 7/8) * 2^31 * C)           // check bounds
            return (7, 31)                      // return maximum
        else
            b = floor (log2(v / C))             // round down
            a = floor ((v / (2^b * C) - 1) * 8) // round down
            return (a, b)