[SNMP4J] More Info About Counter64 Bug

[Jim Doble]

I've been testing one of the proposed fixes to the problem in the
getBERLength method in the Counter64 class, and noticed that the code I
proposed needs a modification to handle the case where the Java will treat
the long value as negative (because a 64 bit unsigned value is being
represented as a Java long, which is a 64 bit signed value. The modified
code is:

public int getBERLength() {
  if (value < 0L) {
    return 11;
  }
  if (value < 0x80L) {
    return 3;
  }
  if (value < 0x8000L) {
    return 4;
  }
  if (value < 0x800000L) {
    return 5;
  }
  if (value < 0x80000000L) {
    return 6;
  }
  if (value < 0x8000000000L) {
    return 7;
  }
  if (value < 0x800000000000L) {
    return 8;
  }
  if (value < 0x80000000000000L) {
    return 9;
  }
  return 10;
}

A similar approach, which looks a little more complicated but might be
faster if the values are uniformly distributed across the entire range of
possible values is to essentially perform the equivalent of a binary search:

public int getBERLength() {
  if (value < 0L) {
    return 11;
  }
  if (value < 0x80000000L) {
    if (value < 0x8000L) {
	if (value < 0x80L) {
	  return 3;
	}
      else {
	  return 4;
	}
    }
    else {
	if (value < 0x800000L) {
	  return 5;
	}
      else {
	  return 6;
	}
    }
  }
  else {
    if (value < 0x800000000000L) {
	if (value < 0x8000000000L) {
	  return 7;
	}
      else {
	  return 8;
	}
    }
    else {
	if (value < 0x80000000000000L) {
	  return 9;
	}
      else {
	  return 10;
	}
    }
  }
}

If there is a preference for more concise code, the same logic can be
expressed as:

public int getBERLength() {
  if (value < 0L) {
    return 11;
  }
  if (value < 0x80000000L) {
    if (value < 0x8000L) {
	return value < 0x80L ? 3 : 4;
    }
    return value < 0x800000L ? 5 : 6;
  }
  if (value < 0x800000000000L) {
    return value < 0x8000000000L ? 7 : 8;
  }
  return value < 0x80000000000000L ? 9 : 10;
}