The BBC and Master Computer Public Domain Library
B71D GOTO
Submitted by Steve Fewell
Description:
Call routine &B82A to get the Line Number after the GOTO keyword, Issue 'No such line' error if the Line doesn't exist
and set &3D-&3E to the start address of the specified Program Line.
Call routine &9BA6 to check that the statement terminates correctly with a ':', '<cr>' or 'ELSE-token' character,
issuing 'Syntax error' if it doesn't.
If the TRACE flag (location &20) is not zero, then call routine &9C4B to check that TRACE is on, and that the
Line Number (locationed in the IWA) is in the specified TRACE range, if it is then the Line number will be displayed on
the screen.
-
Set BASIC Text Pointer A to the start of the specified program line, by:
- * [&B72A] Set #&0A (the BASIC Text Pointer A Offset) to 4 (a pointer to the first character of the
- Program Line (skipping the preceding Line number (3 bytes) and Next Line offset (1 byte) values).
- * Set &0B (the BASIC Text Pointer A LSB) to the Line Number Start Address LSB value at location &3D
- * Set &0C (the BASIC Text Pointer A MSB) to the Line Number Start Address MSB value at location &3E
- Program Line (skipping the preceding Line number (3 bytes) and Next Line offset (1 byte) values).
Disassembly for the GOTO routine
| B71D | * | 032 042 184 | 20 2A B8 | JSR &B82A Get Line Number & find Program Address of the Line Number |
| B720 | 032 166 155 | 20 A6 9B | JSR &9BA6 Check end of Statement | |
| B723 | 165 032 | A5 20 | LDA &20 | |
| B725 | 240 003 | F0 03 | BEQ 3 --> &B72A | |
| B727 | K | 032 075 156 | 20 4B 9C | JSR &9C4B Display current line number (IWA) on screen [if TRACE is on] |
| B72A | 160 004 | A0 04 | LDY#&04 | |
| B72C | 132 010 | 84 0A | STY &0A | |
| B72E | = | 164 061 | A4 3D | LDY &3D |
| B730 | > | 165 062 | A5 3E | LDA &3E |
| B732 | 132 011 | 84 0B | STY &0B | |
| B734 | 133 012 | 85 0C | STA &0C | |
| B736 | L | 076 011 144 | 4C 0B 90 | JMP &900B Process next BASIC program statement |
