! ARITHMETIC ROUTINE (SORT OF DOUBLE WORD)

!W.S.C. 24TH FEB 1977

!LAST UPDATED 25/03/77   09:45

%CONTROL K'001000'
%EXTERNALROUTINE ARITH(%INTEGERNAME N1,N2,%INTEGER BY1,BY2,OP)

   !N1 & N2 ARE DOUBLE WORD INTEGERS WITH UP TO 100 IN N2,
   !THE 1000'S IN N1.DITTO BY1 AND BY2.THE RESULT IS PUT
   !INTO N1 &N2. FOR MPY AND DIV BY1 IS ASSUMED TO BE ZERO.
   !   OP MAY BE ONE OF THE FOLLOWING VALUES:-

%CONSTINTEGER ADD=0
%CONSTINTEGER SUB=1
%CONSTINTEGER MPY=2
%CONSTINTEGER DIV=3

%SWITCH SW(0:3)

%INTEGER TEMP,I,BT2,T1,T2,R1,MB,CAR,R2

%ROUTINE AD(%INTEGER B1,B2,%INTEGERNAME M1,M2)
   %INTEGER TEMP
   M2=M2+B2
   TEMP=M2//1000
   M2=M2-(TEMP*1000)
   M1=M1+B1+TEMP
%END

%ROUTINE SB(%INTEGER B1,B2)
   CAR=0
   TEMP=0
   %IF B2>N2 %START
      TEMP=B2//1000
      %IF N2<B2-(TEMP*1000) %THEN N2=N2+1000 %AND CAR=1
   %FINISH
   N2=N2-(B2-(TEMP*1000))
   N1=N1-B1-TEMP-CAR
%END

!     CODE  STARTS  HERE  !

->SW(OP)

SW(ADD):AD(BY1,BY2,N1,N2)
        %RETURN

SW(SUB):SB(BY1,BY2)
        %RETURN

SW(MPY):R1=0
        R2=0
        MB=BY2
        %WHILE MB#0 %CYCLE
           BT2=MB-((MB//10)*10)
           T2=N2*BT2
           T1=N1*BT2
           TEMP=T2//1000
           T1=T1+TEMP
           T2=T2-(TEMP*1000)
           AD(T1,T2,R1,R2)
           MB=MB//10
           N2=N2*10
           TEMP=N2//1000
           N1=(N1*10)+TEMP
           N2=N2-(TEMP*1000)
        %REPEAT
        N1=R1
        N2=R2
        %RETURN

SW(DIV):%IF BY2=0 %START
           PRINTSTRING('DIVIDE BY ZERO')
           NEWLINE
           %STOP
        %FINISH
        %IF BY2>3276 %START
           BT2=BY2
           %WHILE BT2=(BT2//10)*10 %CYCLE
              BT2=BT2//10
              R1=N1-(N1//10)*10
              N1=N1//10
              N2=(N2+(R1*1000))//10
           %REPEAT
           %RETURN %IF BT2=1
           T1=BT2//1000
           T2=BT2-(T1*1000)
           R1=0
           R2=0
           %WHILE N1>T1 %OR (N1=T1 %AND N2>=T2) %CYCLE
              AD(0,1,R1,R2)
              SB(T1,T2)
           %REPEAT
        %FINISH %ELSE %START
           BT2=N2
           R1=N1//BY2
           R2=0
           T2=R1*BY2
           N1=N1-T2
           I=100
WRITE(R1,5);WRITE(R2,5);WRITE(T2,5);WRITE(I,5);NEWLINE
WRITE(N1,5);WRITE(N2,5);WRITE(BY2,5);NEWLINE
           %WHILE I#0 %CYCLE
              TEMP=BT2//I
WRITE(TEMP,5)
              T1=(N1*10)+TEMP
WRITE(T1,5)
              T2=T1//BY2
WRITE(T2,5)
              R2=R2+(T2*I)
WRITE(R2,5);NEWLINE
              N1=T1-(T2*BY2)
WRITE(N1,5)
              BT2=BT2-(TEMP*I)
WRITE(BT2,5)
              I=I//10
WRITE(I,5);NEWLINE
           %REPEAT
        %FINISH
        N1=R1
        N2=R2

%END
%ENDOFFILE