Prim numbers and random values

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Hi Lucas,

this is probably an absolute newbie question, sorry for that, but maybe you can give me a hint nevertheless:

I experimented with your random-function and reworked it into a subprogram to be able to use it on the mainframe too. I keep getting very puzzling results, though - in short: it seems to work on PC but not on the mainframe!? :? I copied both the subprogram and the calling program from my PC-environment to my library on the mainframe so I am using the exact same coding. On PC I get a desired series of pseudo-random numbers, on the mainframe (IBM Host, z/OS), however, I get the same number over and over again. I assume this has to do with the F8 format (or the conversion F8 to I4 ) - does that work differently on the mainframe???

Here’s your function as subprogram (I added some “writes” for testing):

* (Pseudo-) Zufallszahl
*
* Function .... RAND
* Author ...... Lukas Hundemer
* Last edit ... 2006-07-20
* Copyright ... Software AG 2006. All rights reserved.
*
* Description
* Returns random number 0 <= RAND < 1
*
* Note
* It uses the independent variable +RAND when called iple times
*
* Anmerkung: Da Funktionen und Funktionsaufrufe auf dem HOST (NAT 4)
*            nicht implementiert sind, habe ich die Funktion in ein
*            Subprogram umgewandelt.
*
* ************************************************************************************
DEFINE DATA
PARAMETER
1 #RAND-F8 ( F8 )
LOCAL
1 #PRIM (I4) INIT <2147483629>  /* big I4 prim number, 2 as prim element
1 #P1 (I4)  /* p-1
1 #PH (I4)  /* (p-1)/2
1 #VAL (I4)
1 #VAL1 (I4)
1 #STCL ( B8 )
1 REDEFINE #STCL
  2 #S1 (B2)
  2 #T4 (I4)  /* random start if required
  2 REDEFINE #T4
    3 #T4A (B3)
    3 #T1 (B1)  /* 0 - 255 random repeat
  2 #S2 (B2)
1 #R2 (I2)
1 REDEFINE #R2
  2 #R21 (B1)
  2 #R22 (B1)
1 #I (I4)
1 #J (N4)
1 #F ( F8 )
INDEPENDENT
1 +RAND (I4)
END-DEFINE
*
#P1 := #PRIM - 1
#PH := #P1 / 2
MOVE *TIMESTMP TO #STCL
*
IF +RAND = 0  /* first call
  MOVE #T4 TO #VAL  /* random time
  IF #VAL >= #P1  /* mod p-1
    #VAL := #VAL - #P1
  ELSE
    REPEAT
      IF #VAL >= 0
        ESCAPE BOTTOM
      ELSE
        #VAL := #VAL + #P1
      END-IF
    END-REPEAT
  END-IF
  +RAND := #VAL + 1   /* range 1 to p-1
END-IF
*
#VAL := +RAND
WRITE *PROGRAM '=' #VAL '=' +RAND
RESET #R22
MOVE #T1 TO #R21  /* get unsigned (i1)
*
FOR #I = 1 TO #R2 /* ** rand(i1)
  IF #VAL > #PH  /*   2 * #val > p
    #VAL1 := #PRIM - #VAL /* avoid overflow
    #VAL := #VAL - #VAL1 /* = v-(p-v) = 2v-p = 2v (mod p)
  ELSE
    ADD #VAL TO #VAL
  END-IF
END-FOR
*
MOVE #VAL TO +RAND
#F := #VAL - 1
WRITE *PROGRAM '=' #F
#RAND-F8 := #F / #P1
*
END

Here’s the calling PGM:

DEFINE DATA LOCAL
1 #RUECK ( F8 )
1 #CNTR (I2)
1 #RUECK-I4 (I4)
END-DEFINE
*
FOR #CNTR = 1 TO 8
  CALLNAT '#DHRANDN' #RUECK
  #RUECK-I4 := 10 * #RUECK + 1
  PRINT '=' #RUECK '=' #RUECK-I4
END-FOR
*
END