By Adrian Dery
Basic Range Delete
Getting tired of deleting BASIC statements one line at a time? This is an Assembly Language program that will delete any number of lines by simply giving it the FIRST and LAST line numbers in the range.
The BASIC program in Listing 1 is easy to use and requires no memory other than Page Six. Just load and run it, first thing after turning on the computer and the Range Delete function is available as long as the power stays on. System Reset, Break and CLOAD's do not affect it, but be careful not to load anything else in Page Six.
The next step is to set up an easy method to access the Assembly program, by entering a line something like:
32767 INPUT FIRST, LAST:X=USR(1536,FIRST,LAST)
Then, from immediate mode, enter:
DEL = 32767
Remember that LOAD's and CLOAD's will wipe out line 32767 and a RUN will reset DEL to zero. Therefore you will have to repeat one or both of the above as necessary.
Complete the above steps and you are ready to do any kind of BASIC editing. To delete any number of lines in a range, enter G. DEL from immediate model and BASIC will respond with the ? prompt. Enter the FIRST and LAST Line numbers in the range and all the lines in between will disappear.
Another useful feature of this program is that the USR call can be dynamically executed from a running BASIC program. This makes it a super memory saver if you have a program that uses a lot of memory to initialize strings or memory from literals or DATA statements. Put a USR call at the end of the initialization routine with the FIRST and LAST line numbers of the routine as parameters and the whole routine will be automatically deleted. Just make sure that the USR call, if it's going to be deleted, is on a line by itself or is the last statement on the last line.
One precaution is necessary. The USR call must be on a line number equal to or higher than the highest line to be deleted. The reason is that memory taken up by the deleted lines is reclaimed by the lines above the deleted section. Not only do the lines above the deleted section get moved down into lower memory, but also, a few BASIC internal pointers have to get adjusted by the amount deleted. One of them is the pointer to the current statement being executed, which is the USR call. The amount of Assembly code needed to adjust the BASIC pointer did not seem in line with the advantages. Therefore, the Delete Program assumes that this pointer has to be adjusted and does it.
0100 *= 1536 0101 STMTAB = 136 0105 STMCUR = 138 0110 MEMTOP = 144 0115 HIADR = 203 0120 LOADR = 205 0200 ; 0201 ;GET FIRST LINE NUMBER 0202 ; 0205 CLD 0210 PLA 0215 PLA 0220 STA LINNBR+1 0225 PLA 0230 STA LINNBR 0235 ; 0236 ;LOCATE ADDRESS OF 0237 ;FIRST LINE NUMBER 0238 ; 0240 LDA STMTAB 0241 STA HIADR 0242 LDA STMTAB+1 0243 STA HIADR+1 0245 JSR SRCHLN 0260 ; 0261 ;SAVE ADDRESS OF FIRST 0262 ;LINE NUMBER 0263 ; 0265 LDA HIADR 0270 STA LOADR 0275 LDA HIADR+1 0280 STA LOADR+1 0300 ; 0301 ;GET LAST LINE NUMER 0302 ;PLUS 1 0303 ;AND IT'S ADDRESS 0304 ; 0305 PLA 0310 STA LINNBR+1 0315 PLA 0320 CLC 0325 ADC #1 0330 STA LINNBR 0335 BCC GETTO 0340 INC LINNBR+1 0345 GETTO JSR SRCHLN 0360 ; 0361 ;LENGTH TO MOVE = 0362 ;MEMTOP - 0363 ;ADDRESS OF LAST LINE 0364 ; 0365 SEC 0370 LDA MEMTOP 0375 SBC HIADR 0380 STA MOVLEN 0385 LDA MEMTOP+1 0390 SBC HIADR+1 0395 STA MOVLEN+1 0400 ; 0401 ;LENGTH OF POINTER 0402 ;ADJUSTMENT = 0403 ;HIADR - LOADR 0404 ; 0405 SEC 0410 LDA HIADR 0415 SBC LOADR 0420 STA MEMADJ 0425 LDA HIADR+1 0430 SBC LOADR+1 0435 STA MEMADJ+1 0445 ; 0446 ;REMOVE DELETED SPACE 0447 ; 0450 LDY #0 0452 LDX MOVLEN+1 0454 BEQ NOPG 0456 NXT256 LDA (HIADR),Y 0458 STA (LOADR),Y 0460 INY 0462 BNE NXT256 0464 INC HIADR+1 0466 INC LOADR+1 0468 DEX 0470 BNE NXT256 0472 NOPG CPY MOVLEN 0474 BEQ ADJPNT 0476 LDA (HIADR),Y 0478 STA (LOADR),Y 0480 INY 0482 BNE NOPG 0500 ; 0501 ;ADJUST BASIC POINTERS 0502 ; 0505 ADJPNT LDX #0 0510 LDY #4 0515 ADJLOP SEC 0520 LDA STMCUR,X 0525 SBC MEMADJ 0530 STA STMCUR,X 0535 LDA STMCUR+1,X 0540 SBC MEMADJ+1 0545 STA STMCUR+1,X 0550 INX 0555 INX 0560 DEY 0565 BNE ADJLOP 0566 ; 0567 ;RETURN TO USER 0568 ; 0570 RTS 0700 ; 0701 ;SEARCH BASIC'S 0702 ;STATEMENT TABLE FOR A 0703 ;LINE NUMBER => LINNBR 0704 ; 0705 SRCHLN LDY #2 0710 LDA (HIADR),Y 0715 STA LINLEN 0720 DEY 0725 LDA (HIADR),Y 0727 DEY 0730 CMP #128 0735 BEQ LINRET 0740 CMP LINNBR+1 0745 BEQ LOOKLO 0750 BCS LINRET 0755 BCC BMPLIN 0760 LOOKLO LDA (HIADR),Y 0765 CMP LINNBR 0770 BCS LINRET 0775 BMPLIN CLC 0785 LDA LINLEN 0790 ADC HIADR 0795 STA HIADR 0800 BCC SRCHLN 0805 INC HIADR+1 0810 BNE SRCHLN 0820 LINRET RTS 0959 ; 0960 MOVLEN .BYTE 0 0961 .BYTE 0 0965 LINNBR .BYTE 0 0966 .BYTE 0 0970 MEMADJ .BYTE 0 0971 .BYTE 0 0975 LINLEN .BYTE 0 0999 .END