*********************************************************************
*  ACKERMAN PROGRAM                                                 *
*                                                                   *
*  Input is M and N (PL16)                                          *
*  Output is RESULT (PL16)                                          *
*                                                                   *
*********************************************************************
*
P14MW1   ZMFACC CODE,START,RUNSYS=390,NAME='Martin Ward'
*
* START OF ACKERMAN COMPUTATION: RESULT = A(M,N)
*
ACKERMAN EQU   *
         ZAP   RESULT,N
         CP    M,=P'1'
	 BH    M2
* M=0 or 1, RESULT=N+M+1
         AP    RESULT,M
         BO    TOOBIG
         AP    RESULT,=P'1'
         BO    TOOBIG
         B     ACK999
*
M2       EQU   *
         CP    M,=P'2'
         BH    M3
* M=2, RESULT=2N+3
         MP    RESULT,=P'2'
         AP    RESULT,=P'3'
         BO    TOOBIG
         B     ACK999
*
M3       EQU   *
         CP    M,=P'3'
         BH    M4
* M=3, RESULT=2**(N+3)-3
         CP    N,=P'99'  A(3,99) is the limit for 31 digits
         BH    TOOBIG
         ZAP   WORK,N
	 AP    WORK,=P'3'
	 ZAP   RESULT,=P'1'
M3LOOP	 CP    WORK,=P'0'
	 BE    M3EXIT
         MP    RESULT,=P'2'
         SP    WORK,=P'1'
         B     M3LOOP
M3EXIT   SP    RESULT,=P'3'
         B     ACK999
*
M4       EQU   *
         CP    M,=P'4'
         BH    M5
* M=4, CHECK N
         CP    N,=P'0'
         BH    M51
         ZAP   RESULT,A40
         B     ACK999
M51      CP    N,=P'1'
         BH    TOOBIG
         ZAP   RESULT,A41
         B     ACK999
*
M5       EQU   *
         CP    M,=P'5'
         BH    TOOBIG
* M=5, CHECK N
         CP    N,=P'0'
         BH    TOOBIG
         ZAP   RESULT,A50
         B     ACK999
TOOBIG   ZAP   RESULT,=P'-1'
*
ACK999   EQU   *
*
         ZMFACC CODE,END
*
         ZMFACC INPUT,START
M        DC    PL16'4'
N        DC    PL16'1'
         ZMFACC INPUT,END
         ZMFACC OUTPUT,START
RESULT   DC    PL16'0'
         ZMFACC OUTPUT,END
WORK     DC    PL16'0'                 USED TO COMPUTE 2**(N+3)
A40      DC    P'13'                   A(4,0)
A41      DC    P'65533'                A(4,1)
* NOTE: A(4,2) = 2**65536-3 IS TOO BIG FOR PL16
A50      DC    P'65533'                A(5,0)
* ALL LARGER VALUES OF M ARE TOO BIG FOR PL16
*
         LTORG
*
         END