The BBC and Master Computer Public Domain Library

BE93 EXT =

Submitted by Steve Fewell

Description:

Set A to 3 (this is the OSARGS action number for 'Set EXT for an open file').

Call &BE99 (in the 'PTR =' routine) to:

* Store A to the 6502 stack

* Check for '#' character ('Missing #' error if not found)

* Get Integer result of expression (file channel number) and store LSB byte to the 6502 stack

* Check for '=' character ('Syntax error' if not found)

* Get the result of expression and convert to Integer (IWA) if Floating-Point value, or issue 'Type mismatch'

   error if String value

* Check for the end of statement ('Syntax error' if ':', '<cr>' or 'ELSE' not found)

* Retrieve Y from the 6502 stack (the file channel number)

* Set X to #&2A (the start of the 4-byte zero page parameter block that holds the new file length (EXT) value)

* Retrieve A from the 6502 stack (this retrieves #&03, the OSARGS action for 'set EXT value')

* Call the Operating System OSARGS routine (&FFDA) to set the EXT value for the open file (specified by channel Y)

* Jump to &9005 to start processing the next command line or program statement

Disassembly for the EXT = routine