Technical Blog Post
Floating Point Numbers with IBM BPM
A quick overview of numbers
Z - Set of all negative and positive integers (…-2,-1,0,1,2…)
The set of integers (Z) can be expressed in base 2. Each place is a power of 2.
|power of 2||2^7||2^6||2^5||2^4||2^3||2^2||2^1||2^0|
Decimal and binary representation of some integers
Integers (Z) can easily be expressed as binary digits. However, not all fractions (rational numbers) can be represented in binary. The reason is converting these to binary results in an repeating number. ⇒See this article for information on decimals and binary, and here on ⇒StackOverFlow. This is also a study of numerical analysis.
How do you solve this problem?
Use a 3rd party math library. For my example I used the ⇒BigDecimal.js library. To make the BigDecimal.js library to work with BPM and our class loader, use the uncompressed JS files and put the MathContext.js contents pasted before the BigDecimal.js file in a single file. Then add this file as a managed asset to the application. From here you can then create statements like this.
var a = new BigDecimal(tw.local.n1.toString());
var b = new BigDecimal(tw.local.n2.toString());
a = a.add(b);
tw.local.n3 = a.toString();
Then you can get the values you want. For multiplying decimal values, these can easily add extra digits. For this you can add statement like
a = a.setScale(tw.local.customScale,
Where tw.local.customScale is an integer with the default value of 2. To enable the rounding, click the round in the BigDecimal example or the floor checkbox on the decimal version. For the plain JS Decimal version, you can use the technique of multiply by 100 and then floor, then divide by 100. Here I have an environment variable holding the value 100, so it could be changed to 1, 10, 1000 and so on.
var d1 = tw.local.n1;
var d2 = tw.local.n2;
var d3 = d1+d2;
tw.local.n3 = Math.floor(d3*tw.env.precisionDecimal) / tw.env.precisionDecimal;
The Example TWX file is available in the BPM L2 Sample Apps section.
Change History: 1/19/2018 - Updated links to GIT repository
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