How to use floating point numbers in CLDC 1.0

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30 Sep
2009

Article Review by Larry101 (20090930)

This article introduces one of the several libraries that exist for getting around the limitation of CLDC 1.0 (no floating point primitive types). This article gives a brief introduction of the MicroFloat library, which provides methods for performing arithmetic using floating point numbers, using values stored in long variable types to simulate double and float primitive types. The article also demonstrates how the necessary constants the library uses can be generated using a simple call in Java SE to the toHexString method of the Long class. A useful article for those who need to perform floating point mathematics in CLDC 1.0.

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Created: firt (01 Apr 2007)

Last edited: hamishwillee (19 Jul 2012)

If you are working for targets with MIDP 1.0, you'll probably have to deal with CLDC 1.0, with the lack of floating point support. So, you can't use float or double types in your code.

This tip helps you in these situation with an Open Source library from David Clausen called MicroFloat. The use of this library is very slow (because of the lack of floating hardware on the device) but it will work.

MicroFloat is a Java software library for doing IEEE-754 floating-point math on small devices which don't have native support for floating-point types. Basically this means Java-powered mobile phones (J2ME CLDC 1.0).

In this package you'll get support for 32-bit "float" and 64-bit "double" data types, including all primitive operations supported by Java SE (add, subtract, multiply, divide, mod, comparisons, typecasts) as well as a full reproduction of all methods in java.lang.Math (sin, cos, exp, pow, log, etc.). In theory, these operations should return results which are fully compliant with the IEEE-754 and Java SE specs.

You can download it from http://www.dclausen.net/projects/microfloat// and browse the documentation in JavaDoc format in http://www.dclausen.net/projects/microfloat///javadoc/index.html

Then, you've just change your CLDC 1.1 code like this:

// old function using native floating point arithmetic in CLDC 1.1
public double averageThreeNumbers(double a, double b, double c) {
  return (a + b + c) / 3;
}
 
// new function using MicroFloat arithmetic in CLDC 1.0
import net.dclausen.microfloat.*;
 
private static final long THREE = 0x4008000000000000L; 
public long averageThreeNumbers(long a, long b, long c) {
  return MicroDouble.div(MicroDouble.add(MicroDouble.add(a, b), c), THREE);
}

You can obtain constants like THREE above by having a simple J2SE helper class with a main method like this:

// Desktop Console Java SE application to get a MicroFloat constant
public static void main(String[] args) {
  System.out.println(Long.toHexString(Double.doubleToLongBits(3)));
}