The BBC and Master Computer Public Domain Library
BAEB Tokenise Command Line and Insert Line into Program
Submitted by Steve Fewell
Routine:Tokenise
Name: Tokenise Command Line (and insert into program if line number found)
Starting Address: &BAEB
Entry criteria: &0700-&07EF (the command line input location) contains the program text to tokenise
Exit: C = 0 if the command is a direct command and not part of a program - this inputt is requried to be executed
immediately.
C = 1 if a program line was entered (and inserted into the program) - not required to be executed immediately.
Description:
Set &28 (OPT flag) to #&FF.
Set &3C to #&FF (this tells the &8DB2 routine to Check for a Line Number at the start of the line).
Call routine &BBCF to initialise the Program start address (&1C, &1D), Stack pointer & REPEAT/FOR/GOSUB
levels and also reset the top bit of the LISTO flag (#&1F, to cancel *EDIT mode).
Note: variables are NOT reset by this initialisation.
Set pointer (&37, &38) to point to BASIC Text Pointer A (i.e. the Command Line input text).
Zero &3B (to initialise routine &8DB2 to be in 'Start of Statement' mode).
Zero BASIC Text pointer A offset (as we will start processing from the beginning of the command line text).
Call routine &8DB2 to tokenise the command line text pointed to by (&37, &38).
Call routine &9B1E to set the IWA to the Line Number (which is now tokenised) at the location pointed to by BASIC Text
Pointer A (i.e. the start of the command line input), and set Y to point to the next character after the Line Number.
If the carry flag is not set then a Line Number was not present, so exit as we do not need to alter the current BASIC
program at all (no lines to insert, change or delete).
[&BB08] If the LISTO flag (&1F) is not 0, then skip any multiple leading spaces after the line number - meaning
that a maximum of 1 space character will be kept after the line number. This enables helps LIST command with its
formatting. Additionally, if no spaces are specified, then none will be stored.
Set location &3B to Y - that is the offset (from &0700) to the start of the program line (after the Line Number),
with any extra leading spaces ignored (if the LISTO flag is not 0).
Call routine &BA98 to remove the line number (specified in the IWA) from the program (if it is found).
Set location &3C to 7 and Y to 0.
Now pointer (&3B, &3C) points to the first character (after the Line Number) of the tokenised program line,
and Y contains the offset (from this pointer) of the current character that we are working with.
If the start of the program line (pointed to by (&3B, &3C)) contains the '<cr>' character then exit as
there is no line to insert - and we have deleted the specified line from the program (as per the user's request).
[&BB26] Search for the next '<cr>' character and set Y to the length of the program line (excluding the Line Number
and the '<cr>' character.
Reduce Y (if necessary) so that it points to the last non-space character on the line. This is done in order to skip any
trailing spaces on the command line.
Store a '<cr>' character at location (&37, &38 + offset Y+1) [i.e. at the end of the program line].
Add 4 to Y (to take into account the 4-byte tokenised Line Number [1 byte for Line Number token and 3 for the Line
Number value]).
Store Y (the line length) in location &3F.
Set &39-&3A to TOP.
Update TOP (by adding Y tm the TOP value via routine &BE04).
Set (&37, &38) to the new TOP value.
Set Y to 0 (Y is 1 on return from &BE04).
If HIMEM (&06, &07) is less than the new TOP value then there is not enough space for the program line to be stored,
so:
* Call &BBAC to check that the program can be read correctly (and to set the correct TOP value).
[at this stage the new/changed Line will not be present in the program at all].
* generate a 'LINE space' error.
-
[&BB6B] Copy bytes from the old TOP location (&39, &3A) to the new TOP location (&37, &38), starting
with the last character in the program as follows:
- * Copy character from (&39, &3A) + Y to location (&37, &38) + Y
- * If Y is 0 then decrement old TOP MSB byte (&3A) and new TOP MSB byte (&38).
- * [&BB76] decrement Y
- * Set A (LSB byte) and X (MSB byte) to the old TOP value plus Y.
- * [&BB7F] if (&3D, &3E) [which is a pointer to the program line that is greater than or equal to the line that
- we are inserting, as set by routine &BA98] is less than the old TOP value + Y (stored in: A (LSB byte), X (MSB byte))
- then jump back to &BB6B to copy the next byte from the old TOP location to the new TOP location.
- * If Y is 0 then decrement old TOP MSB byte (&3A) and new TOP MSB byte (&38).
line has just been copied to the new TOP location, so now we have space for the new program line to be inserted.
Store the program line number MSB (from the IWA byte &2B) in the first byte of the reserved program space pointed to
by (&3D-&3E).
Store the program line number LSB (from the IWA byte &2A) in the second byte of the reserved program space pointed to
by (&3D-&3E).
Store the line length (from location &3F) in the third byte of the reserved program space pointed to by (&3D-&3E).
Add 4 (Y + 1) to the (&3D-&3E) pointer.
Copy the new BASIC program (from location (&3B, &3C), i.e. the command line) to the new location (&3D, &3E).
(The program line is terminated by the '<cr>' character).
Exit with Carry flag set.
Note: the lines before the inserted line do not need to be moved, only the lines between the inserted line and the old TOP
location.
Disassembly for the 'Tokenise Command Line and Insert Line into Program' routine
| BAEB | 162 255 | A2 FF | LDX#&FF | |
| BAED | ( | 134 040 | 86 28 | STX &28 |
| BAEF | < | 134 060 | 86 3C | STX &3C |
| BAF1 | 032 207 187 | 20 CF BB | JSR &BBCF Initialise Program start address, Stack pointer, *EDIT mode & REPEAT/FOR/GOSUB levels | |
| BAF4 | 165 011 | A5 0B | LDA &0B | |
| BAF6 | 7 | 133 055 | 85 37 | STA &37 |
| BAF8 | 165 012 | A5 0C | LDA &0C | |
| BAFA | 8 | 133 056 | 85 38 | STA &38 |
| BAFC | d; | 100 059 | 64 3B | STZ &3B |
| BAFE | d | 100 010 | 64 0A | STZ &0A |
| BB00 | 032 178 141 | 20 B2 8D | JSR &8DB2 Tokenise Command Line | |
| BB03 | 032 030 155 | 20 1E 9B | JSR &9B1E Detokenise the Line Number at PTR A & Set IWA to the Line Number value | |
| BB06 | 144 226 | 90 E2 | BCC -30 --> &BAEA [RTS] | |
| BB08 | 165 031 | A5 1F | LDA &1F | |
| BB0A | 240 009 | F0 09 | BEQ 9 --> &BB15 | |
| BB0C | 185 000 007 | B9 00 07 | LDA &0700,Y | |
| BB0F | 200 | C8 | INY | |
| BB10 | 201 032 | C9 20 | CMP#&20 | |
| BB12 | 240 248 | F0 F8 | BEQ -8 --> &BB0C | |
| BB14 | 136 | 88 | DEY | |
| BB15 | ; | 132 059 | 84 3B | STY &3B |
| BB17 | 032 152 186 | 20 98 BA | JSR &BA98 Remove Line Number (specified in IWA) from Program | |
| BB1A | 160 007 | A0 07 | LDY#&07 | |
| BB1C | < | 132 060 | 84 3C | STY &3C |
| BB1E | 160 000 | A0 00 | LDY#&00 | |
| BB20 | 169 013 | A9 0D | LDA#&0D | |
| BB22 | ; | 210 059 | D2 3B | CMP (&3B) |
| BB24 | 240 196 | F0 C4 | BEQ -60 --> &BAEA [RTS] | |
| BB26 | 200 | C8 | INY | |
| BB27 | ; | 209 059 | D1 3B | CMP (&3B),Y |
| BB29 | 208 251 | D0 FB | BNE -5 --> &BB26 | |
| BB2B | 169 032 | A9 20 | LDA#&20 | |
| BB2D | 136 | 88 | DEY | |
| BB2E | 240 004 | F0 04 | BEQ 4 --> &BB34 | |
| BB30 | ; | 209 059 | D1 3B | CMP (&3B),Y |
| BB32 | 240 249 | F0 F9 | BEQ -7 --> &BB2D | |
| BB34 | 200 | C8 | INY | |
| BB35 | 169 013 | A9 0D | LDA#&0D | |
| BB37 | ; | 145 059 | 91 3B | STA (&3B),Y |
| BB39 | 200 | C8 | INY | |
| BB3A | 200 | C8 | INY | |
| BB3B | 200 | C8 | INY | |
| BB3C | 200 | C8 | INY | |
| BB3D | ? | 132 063 | 84 3F | STY &3F |
| BB3F | 165 018 | A5 12 | LDA &12 | |
| BB41 | 9 | 133 057 | 85 39 | STA &39 |
| BB43 | 165 019 | A5 13 | LDA &13 | |
| BB45 | : | 133 058 | 85 3A | STA &3A |
| BB47 | 032 004 190 | 20 04 BE | JSR &BE04 Update TOP (add Y to TOP value, set Y to 1 & exit) | |
| BB4A | 7 | 133 055 | 85 37 | STA &37 |
| BB4C | 165 019 | A5 13 | LDA &13 | |
| BB4E | 8 | 133 056 | 85 38 | STA &38 |
| BB50 | 136 | 88 | DEY | |
| BB51 | 165 006 | A5 06 | LDA &06 | |
| BB53 | 197 018 | C5 12 | CMP &12 | |
| BB55 | 165 007 | A5 07 | LDA &07 | |
| BB57 | 229 019 | E5 13 | SBC &13 | |
| BB59 | 176 016 | B0 10 | BCS 16 --> &BB6B | |
| BB5B | 032 229 189 | 20 E5 BD | JSR &BDE5 Check program can be read correctly ('Bad program' message if not) | |
| BB5E | 032 172 187 | 20 AC BB | JSR &BBAC Initialise Page 7 & reset Variable pointers, etc... | |
| BB61 | ... 'LINE space' error ... | |||
| BB6B | 9 | 177 057 | B1 39 | LDA (&39),Y |
| BB6D | 7 | 145 055 | 91 37 | STA (&37),Y |
| BB6F | 152 | 98 | TYA | |
| BB70 | 208 004 | D0 04 | BNE 4 --> &BB76 | |
| BB72 | : | 198 058 | C6 3A | DEC &3A |
| BB74 | 8 | 198 056 | C6 38 | DEC &38 |
| BB76 | 136 | 88 | DEY | |
| BB77 | 152 | 98 | TYA | |
| BB78 | e9 | 101 057 | 65 39 | ADC &39 |
| BB7A | : | 166 058 | A6 3A | LDX &3A |
| BB7C | 144 001 | 90 01 | BCC 1 --> &BB7F | |
| BB7E | 232 | E8 | INX | |
| BB7F | = | 197 061 | C5 3D | CMP &3D |
| BB81 | 138 | 8A | TXA | |
| BB82 | > | 229 062 | E5 3E | SBC &3E |
| BB84 | 176 229 | B0 E5 | BCS -27 --> &BB6B | |
| BB86 | 160 001 | A0 01 | LDY#&01 | |
| BB88 | + | 165 043 | A5 2B | LDA &2B |
| BB8A | = | 145 061 | 91 3D | STA (&3D),Y |
| BB8C | 200 | C8 | INY | |
| BB8D | * | 165 042 | A5 2A | LDA &2A |
| BB8F | = | 145 061 | 91 3D | STA (&3D),Y |
| BB91 | 200 | C8 | INY | |
| BB92 | ? | 165 063 | A5 3F | LDA &3F |
| BB94 | = | 145 061 | 91 3D | STA (&3D),Y |
| BB96 | 8 | 056 | 38 | SEC |
| BB97 | 152 | 98 | TYA | |
| BB98 | e= | 101 061 | 65 3D | ADC &3D |
| BB9A | = | 133 061 | 85 3D | STA &3D |
| BB9C | 144 002 | 90 02 | BCC 2 --> &BBA0 | |
| BB9E | > | 230 062 | E6 3E | INC &3E |
| BBA0 | 160 255 | A0 FF | LDY#&FF | |
| BBA2 | 200 | C8 | INY | |
| BBA3 | ; | 177 059 | B1 3B | LDA (&3B),Y |
| BBA5 | = | 145 061 | 91 3D | STA (&3D),Y |
| BBA7 | 201 013 | C9 0D | CMP#&0D | |
| BBA9 | 208 247 | D0 F7 | BNE -9 --> &BBA2 | |
| BBAB | ` | 096 | 60 | RTS |
