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High School-Level Math in RPG IV

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Back in the 1980s, I created a program called Partner, a productivity tool that included a calendar, a notepad, an adding machine, a command-line interceptor, and an expression analyzer. These applications popped up in different windows to provide a PC-style windowing environment. As far as I know, Partner was the first commercial 5250 application with pop-up windows.

An interesting application in that package was its expression analyzer. This component allowed users to type in a free-format mathematical expression and receive the result. You could even extend the functions by adding your own. That is, Partner did user-written procedures years before ILE was being considered by Paul Remtema and at least a decade before IBM considered adding subprocedures to RPG IV.

The types of math functions Partner was able to perform included high-level mathematical operations, such as sine, cosine, and arctangent hyperbolic. To perform these math functions in RPG, I called an MI program that used the "compute math function" and "compute math function 2" instructions.

While the Partner software continues to run and work on i5/OS more than 20 years after it was first introduced, the ability to perform high-level math continues to elude the RPG IV language even today. Or has it?

With the integration of RPG IV and ILE and the ability to call subprocedures and functions written in other programming languages, IBM has opened up RPG to extensions beyond what is officially implemented in the language.

While I've written about the C runtime library before, the math portion of the C library is intriguing. It supports a rather complete set of high-level math functions that can be utilities from within RPG IV very effectively.

By creating the prototypes for the C math runtime library and binding with the QC2LE binding directory, any high-level math function can be utilized from within RPG.

For example, to calculate the sine of a number, you could use the following:

     H BNDDIR('QC2LE')
     D sin             PR             8F   extProc('sin') 
     D   radians                      8F   Const 
     D mySine          S             11P 9

      /free
          mySine = sin(.05);
      /end-free

Aside from the lack of a leading percent sign (%), these math functions, like all C runtime library functions, work much like built-in functions.

The C math functions have a more programmer-friendly parameter list than the set of CEExxxx math APIs; however, one or two more math functions are available using the APIs.

To illustrate, I've repeated the call to the sine function below, using the API convention. The API name to calculate a sine is CEESDSIN.

 

    D sin             PR                  extProc('CEESDSIN')
     D  fInput                        8F   Const 
     D  fOutput                       8F
     D  apiErrorDS                         LikeDS(QUSEC)
     D                                     OPTIONS(*VARSIZE:*OMIT)

     D fSine           S              8F
     D mySine          S             11P 9

      /free
          callp sin(.05: mySine : *OMIT );
          mySine = fSine;
      /end-free

 

A few differences exist between the C runtime math library and the i5/OS math APIs.

  • The binding directory QC2LE is not required for the CEExxxx APIs (it is required for the C runtime library functions).
  • The C functions return their results via a return value, whereas the APIs require a second parameter to receive the result of the operation.
  • The APIs accept the standardized API error data structure to trap errors; the C functions do not.

The CEExxxx APIs have more flexibility and more choices than the C math functions library, and certainly those additional features are important to compiler writers. But the C functions are much easier to use and should probably be the choice people make when selecting high-level math functions.

As with all CEExxxx APIs, the math APIs' object code is embedded directly into the generated *MODULE object. That is, although a call to the API is coded by the programmer, the compile "inlines" the object code of the API rather than inserting a subprocedure call. This occurs with any API that is prefixed with the letters "CEE" or an underscore (_) .

In my upcoming book RPG TNT: 101 Dynamite Tips and Techniques for RPG IV Programmers, the prototypes for all CEExxxx math APIs as well as the C math functions are included. For space purposes in this article, I've included only the prototypes for the C runtime library math functions below.

High-level mathematical function prototypes:

      /IF NOT DEFINED(C_MATH_PROTOS)
      /DEFINE C_MATH_PROTOS
      **********************************************
      **  From "RPG TNT: 101 Tips and Techniques"
      **  © 2006 by Robert Cozzi, Jr.
      **********************************************
     D acos            PR             8F   extProc('acos')       
     D   radians                      8F   Const           

     D asin            PR             8F   extProc('asin')        
     D   radians                      8F   Const             

     D atan            PR             8F   extProc('atan')       
     D   radians                      8F   Const
                                
     D atan2           PR             8F   extProc('atan2')    
     D   radians1                     8F   Const       
     D   radians2                     8F   Const        

     D ceil            PR             8F   extProc('ceil')       
     D   radians                      8F   Const       

     D cos             PR             8F   extProc('cos')    
     D   radians                      8F   Const      

     D cosh            PR             8F   extProc('cosh')
     D   radians                      8F   Const               

     D exp             PR             8F   extProc('exp')         
     D   radians                      8F   Const           

     D floor           PR             8F   extProc('floor')    
     D   radians                      8F   Const            

     D fmod            PR             8F   extProc('fmod')      
     D   arg1                         8F   Const       
     D   arg2                         8F   Const       
         
     D log             PR             8F   extProc('log')  
     D   radians                      8F   Const 

     D log10           PR             8F   extProc('log10')       
     D   radians                      8F   Const          

     D pow             PR             8F   extProc('pow')
     D**  pow(x:y) = x**Y
     D   x                            8F   Const        
     D   y                            8F   Const         

     D sin             PR             8F   extProc('sin')  
     D   radians                      8F   Const      

     D sinh            PR             8F   extProc('sinh')  
     D   radians                      8F   Const          

     D sqrt            PR             8F   extProc('sqrt')  
     D   radians                      8F   Const       

     D tan             PR             8F   extProc('tan') 
     D   radians                      8F   Const      

     D tanh            PR             8F   extProc('tanh') 
     D   radians                      8F   Const           

     D erf             PR             8F   extProc('erf')
     D   radians                      8F   Const       

     D erfc            PR             8F   extProc('erfc')
     D   radians                      8F   Const       

     D gamma           PR             8F   extProc('gamma')
     D   radians                      8F   Const        

     D hypot           PR             8F   extProc('hypot')
     D   side1                        8F   Const    
     D   side2                        8F   Const    

      /IF DEFINED(BESSEL_FUNC)
      /IF NOT DEFINED(BESSEL_MATH)
      /DEFINE BESSEL_MATH
      **  Bessel functions, first order
     D j0              PR             8F   extProc('j0')      
     D   x                            8F   Const        
     D j1              PR             8F   extProc('j1')       
     D   x                            8F   Const      
     D jn              PR             8F   extProc('jn')        
     D   n                           10I 0 Const       
     D   x                            8F   Const        

      **  Bessel functions, second order
     D y0              PR             8F   extProc('y0')      
     D   x                            8F   Const     
     D y1              PR             8F   extProc('y1')        
     D   x                            8F   Const     
     D yn              PR             8F   extProc('yn')      
     D   n                           10I 0 Const      
     D   x                            8F   Const     
      /ENDIF
      /ENDIF

      /ENDIF      

 

 

 

Bob Cozzi is a programmer/consultant, writer/author, and software developer of the RPG xTools, a popular add-on subprocedure library for RPG IV. His book The Modern RPG Language has been the most widely used RPG programming book for nearly two decades. He, along with others, speaks at and runs the highly-popular RPG World conference for RPG programmers.

 

BOB COZZI

Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.

MC Press books written by Robert Cozzi available now on the MC Press Bookstore.

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