C PROGRAM MODIFY
C MODIFY HAS A LIMITED HOUSEKEEPING LIBRARY,BUT DRAWS ITS ENORMOUS
C POWER FROM ITS EDITING CAPABILITIES.MODIFY CAN COPY OR DELETE VECTORS
C (FROM ANYWHERE IN THE TABLE OF VECTORS).MODIFY INVOKES THE CROSSHAIRS
C TO PINPOINT THE ENDS OF THE VECTORS TO BE CHANGED,AND THEN SHIFTS
C THE ENTIRE TABLE ACCORDINGLY.ALTHOUGH THE PROGRAM SEEMS LENGTHY,IT
C IS FAR SIMPLER THAN IT WOULD BE IF A LINKED LIST WERE USED INSTEAD.
C FURTHERMORE,THE PROGRAM SHIFTS THE LIST INSTANTLY,SO THERE IS NO
C WAITING TIME.
C	D	CHAINS TO DRAW.SV
C	E	ERASES SCREEN
C	G	CHAINS TO GFIC.SV
C	M	PROCEDE TO MODIFY.SV
C	T	CHAINS TO TAPE.SV
C	W	WRITES TABLE
C	X	EXITS FROM PROGRAM
C	1	COPYING MODE
C	2	DELETION MODE
C	3	RETURN TO COMMAND-QUERY MODE
C FORTRAN II
C SR : ERASE.FT / FDIS.FT / ALPHA.FT / RKB.FT / JOY.FT
C CH : TAPE.SV / DRAW.SV / GFIC.SV
C BEARBEITUNG VON DECUS #8-773
	COMMON NTAB,IPT
	DIMENSION NTAB (500,3)
	GOTO 2
1	CALL ERASE
2	CALL FDIS (0,0,767)
	CALL ALPHA
	CALL RKB(K)
C W-WRITE,E-ERASE,T-TAPE,D-DRAW,G-GFIC,M-MODIFY,X-EXIT
	IF (K-1504) 3,13,3
3	IF (K-352) 4,1,4
4	IF (K-1312) 5,10,5
5	IF (K-288) 6,11,6
6	IF (K-480) 7,12,7
7	IF (K-864) 8,15,8
8	IF (K-1568) 2,9,2
9	CALL EXIT
10	CALL CHAIN ('TAPE')
11	CALL CHAIN ('DRAW')
12	CALL CHAIN ('GFIC')
13	DO 14 N=1,IPT
14	CALL FDIS(NTAB(N,1),NTAB(N,2),NTAB(N,3))
	GOTO 2
C MODIFY ROUTINE
15	READ (1,100) I
100	FORMAT ('1=COPY,2=DELETE,3=CANCEL 'I1)
	IF (I-3) 16,2,2
16	CALL JOY (IX,IY,K)
	DO 20 N=1,IPT
	DO 17 N3=0,4
	IF (NTAB(N,2)-IX+N3-2) 17,18,17
17	CONTINUE
	GOTO 20
18	CONTINUE
	DO 19 N3=0,4
	IF (NTAB(N,3)-IY+N3-2) 19,21,19
19	CONTINUE
20	CONTINUE
	WRITE (1,101) 
101	FORMAT ('WRONG COORDINATES')
	GOTO 16
21	NZ=N-1
	NZ2=N
22	CALL JOY(IX,IY,K)
	DO 26 N=NZ2,IPT
	DO 23 N3=0,4
	IF (NTAB(N,2)-IX+N3-2) 23,24,23
23	CONTINUE
	GOTO 26
24	CONTINUE
	DO 25 N3=0,4
	IF (NTAB(N,3)-IY+N3-2) 25,27,25
25	CONTINUE
26	CONTINUE
	WRITE (1,102)
102	FORMAT ('BAD COORDINATES')
	GOTO 22
27	IZ=N-1
	IF (I-1) 2,28,28
C ORDERED PAIRS
28	IF (NZ-IZ) 29,30,30
29	N3=IZ
	IZ=NZ
	NZ=N3
30	IF (I-1)2,33,31
C DELETE FROM N=IZ TO N=NZ BY MOVING UP
31	CONTINUE
	IP=NZ-IZ
	IZ=NZ+1
	NTAB(IZ,1)=0
	IPT=IPT-IP+1
	IZ=IZ-IP+1
	DO 32 N=IZ,IPT
	N2=N+NZ-IZ+1
	NTAB(N,1)=NTAB(N2,1)
	NTAB(N,2)=NTAB(N2,2)
	NTAB(N,3)=NTAB(N2,3)
32	CONTINUE
	CALL ERASE
	GOTO 13
C COPY ROUTINE
33	WRITE (1,103)
103	FORMAT ('NEW POSITION FOR FIRST COORDINATE')
	CALL JOY(KX,KY,K)
	IP=NZ-IZ+1
	IZ=IZ+1
	NZ=NZ+IP
	KX=KX-NTAB(IZ,2)
	KY=KY-NTAB(IZ,3)
	N3=IPT-IZ+NZ
	NTAB(IPT+1,1)=0
	NTAB(IPT+1,2)=NTAB(IZ+1,2)+KX
	NTAB(IPT+1,3)=NTAB(IZ+1,3)+KY
	IPT=IPT+2
	DO 34 N=IPT,N3
	N2=N+IZ-IPT
	NTAB(N,1)=NTAB(N2,1)
	NTAB(N,2)=NTAB(N2,2)+KX
	NTAB(N,3)=NTAB(N2,3)+KY
34	CONTINUE
	IPT=N3
	CALL ERASE
	GOTO 13
	END