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PDP-10 Archives
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decuslib10-02
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43,50247/ibcd.mac
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TITLE IBCD FUNCTION CONVERS ASCII TO BCD
INTERNAL IBCD
;
;PDP-10 ROUTINE TO PULL ASCII CODED CHARACTER FROM ALPHAMERIC
;STRING AND RETURN ITS BCD EQUIVALENT.
;
;THIS IS CALLED AS A FORTRAN FUNCTION WITH 2 ARGUMENTS, THE
;STRING ADDRESS AND THE SERIAL NUMBER OF THE CHARACTER DESIRED.
;THE BCD EQUIVALENT IS RETURNED IN ACCUMULATOR ZERO.
;LTTR=IBCD('THIS IS A STRING',9) IN A FORTRAN PROGRAM
;WOULD GIVE LTTR THE VALUE 17 (OCTAL 21), THE BCD CODE FOR A,
;THE 9TH CHARACTER IN THE STRING.
;
;DONALD BARTH, CHEMISTRY DEPT., HARVARD UNIVERSITY
;
AC0=0 ;AC TO RECEIVE BCD CODE
AC1=1 ;AC USED AS SCRATCH AREA
AC2=16 ;AC CONTAINING RETURN ADDRESS
IBCD: 0
;
;OBTAIN ASCII CHARACTER FROM STRING
;
MOVE AC0, @1(AC2) ;MOVE SERIAL NUMBER TO AC0
ADDI AC0, 4 ;ADD 4 AND DIVIDE BY 5 TO FIND
IDIVI AC0, 5 ;OUT WHAT WORD IN STRING CONTAINS
SOS AC0 ;THE DESIRED CHARACTER.
ADD AC0, (AC2) ;ADD THIS TO STRING ADDRESS.
IMULI AC1, 7 ;MULTIPLY REMAINDER (IN AC0+1)
MOVN AC1, AC1 ;BY 7 (ASCII CHARACTER IS 7 BITS)
ADDI AC1, 35 ;AND SUBTRACT FROM 29 (OCTAL 35)
;TO FIND NUMBER OF BITS TO RIGHT
;OF THE CHARACTER.
LSH AC1, 36 ;SHIFT NUMBER OF BITS RIGHT OF
;BYTE INTO BITS 0-5 OF BYTE POINTER.
IOR AC1, [000700000000] ;PUT BYTE SIZE (7) INTO
;BITS 6-11 OF BYTE POINTER.
HRR AC1, AC0 ;PUT ADDRESS INTO BITS 18-35.
LDB AC0, AC1 ;OBTAIN CODE AND PLACE INTO AC0
;
;CONVERT CODE FROM 7 BIT ASCII TO 6 BIT BCD
;
ADDI AC0, 6 ;ADD 6 TO AC0 TO INSURE THAT
;DIVISION BY 6 WILL GIVE A
;POSITIVE REMAINDER.
IDIVI AC0, 6 ;DIVIDE BY 6, PLACING RESULT IN
;AC0 AND REMAINDER IN AC0+1 (AC1)
SOS AC0 ;SUBTRACT 1 FROM RESULT AND ADD
ADDI AC0, TABLE ;TO ADDRESS OF FIRST TABLE ENTRY
;TO OBTAIN ADDRESS OF TABLE
;ENTRY CONTAINING THE CONVERSION
;INFORMATION FOR PRESENT CHARACTER.
IMULI AC1, 6 ;MULTIPLY BY 6 AND SUBTRACT FROM
MOVN AC1, AC1 ;30 (OCTAL 36) TO OBTAIN NUMBER
ADDI AC1, 36 ;OF BITS TO RIGHT IN TABLE ENTRY.
LSH AC1, 36 ;SHIFT NUMBER OF BITS TO RIGHT
;OF BYTE INTO BITS 0 TO 5.
IOR AC1, [000600000000] ;PUT BYTE SIZE (6) INTO
;BITS 6 TO 11.
HRR AC1, AC0 ;PUT ADDRESS INTO BITS 18-35.
LDB AC0, AC1 ;CONVERT CODE AND PLACE INTO AC0.
JRA AC2, 2(AC2) ;RETURN
;
;FOLLOWING IS THE ASCII TO BCD CONVERSION TABLE.
;
TABLE: BYTE(6) 60,60,60,60,60,60 ;CODES 0- 5
BYTE(6) 60,60,60,60,60,60 ;CODES 6- 11
BYTE(6) 60,60,60,60,60,60 ;CODES 12- 17
BYTE(6) 60,60,60,60,60,60 ;CODES 18- 23
BYTE(6) 60,60,60,60,60,60 ;CODES 24- 29
BYTE(6) 60,60,60,60,60,60 ;CODES 30- 35 , , ,!,",#
BYTE(6) 53,60,60,14,74,34 ;CODES 36- 41 $,%,&,',(,)
BYTE(6) 54,20,73,40,33,61 ;CODES 42- 47 *,+,,,-,.,/
BYTE(6) 0, 1, 2, 3, 4, 5 ;CODES 48- 53 0,1,2,3,4,5
BYTE(6) 6, 7,10,11,60,60 ;CODES 54- 59 6,7,8,9,:,;
BYTE(6) 60,13,60,60,60,21 ;CODES 60- 65 <,=,>,?,@,A
BYTE(6) 22,23,24,25,26,27 ;CODES 66- 71 B,C,D,E,F,G
BYTE(6) 30,31,41,42,43,44 ;CODES 72- 77 H,I,J,K,L,M
BYTE(6) 45,46,47,50,51,62 ;CODES 78- 83 N,O,P,Q,R,S
BYTE(6) 63,64,65,66,67,70 ;CODES 84- 89 T,U,V,W,X,Y
BYTE(6) 71,60,60,60,60,60 ;CODES 90- 95 Z,[,\,],^,_
BYTE(6) 60,21,22,23,24,25 ;CODES 96-101 @,a,b,c,d,e
BYTE(6) 26,27,30,31,41,42 ;CODES 102-107 f,g,h,i,j,k
BYTE(6) 43,44,45,46,47,50 ;CODES 108-113 l,m,n,o,p,q
BYTE(6) 51,62,63,64,65,66 ;CODES 114-119 r,s,t,u,v,w
BYTE(6) 67,70,71,60,60,60 ;CODES 120-125 x,y,z,{,|,
BYTE(6) 60,60, 0, 0, 0, 0 ;CODES 126-127
END