The JMP op-code is a simple instruction to jump by a certain number of lines.

 

Consider the following example :

    if NumDaysInMonth(nCurYear,nCurMonth) >= nDayOfMonth    
        sRESULT = IntToStr(nDayOfMonth)
    else
        sRESULT = ''
    endif

which compiles to :

0011 CALL n001=$0GB(@nCurYear|@nCurMonth)  //NumDaysInMonth
0011 CALL b001=$0CJ(@n001|@nDayOfMonth)  //GreaterOrEqual
0011 IF_001 @b001 jne+0003
0012 CALL sRESULT=$0DH(@nDayOfMonth)  //IntToStr
0013 JMP+0002  //ELSE_001
0014 MOV sRESULT=
0015 ENDF_001

In the above example if the condition is true, the instructions following the IF_001 are all executed and when the interpreter reaches the JMP+0002 instruction it skips the following 2 lines (which correspond to the compiled code for the case when the condition is false).

 

Note that jumps can also be negative.

while nDate < 38000
    nDate = nDate + 1    
endwhile

The above macro compiles to :

0007 CALL b001=$0FD(@nDate|38000)  //LessThan
0007 IF_001 @b001 jne+0003
0008 CALL nDate=$0AA(@nDate|1)  //Add
0009 JMP-0003  //GOIF_001
0009 ENDF_001

which shows how an IF_xxx op-code combined with a JMP op-code replaces the need for an op-code to represent the while loop.

 

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Topic 135400, last updated on 18-Apr-2020