The BBC and Master Computer Public Domain Library

8CEB Replace untokenised ASCII value with a 1-byte token

Submitted by Steve Fewell

Routine:ASCIItoToken
Name: Replace untokenised ASCII value with a 1-byte token
Starting Address: &8CEB
Entry criteria: &37 and &38 point to the start of the ASCII Keyword in the program text.
A contains the token value to replace the ASCII text with.
Y contains the offset to the end character of the Keyword.
Exit: Y = offset pointer to the end of the program command line.

Description:

Store A (the token value) as the first byte of the ASCII Keyword (the location pointed to by (&37, &38)).
Set (&39, &3A) to point to (&37, &38) + Y.
So that (&37, &38) point to the start of the Keyword and (&39, &3A) point to the end of the Keyword.
Copy each character from ((&39, &3A) + 1) to ((&37, &38) + 1) until a <cr> (carriage return character)
is encountered. After a <cr> has been copied, the routine ends, as the rest of the program line has been moved sucessfully
to be positioned directly after the token.

Disassembly for the 'Replace untokenised ASCII value with a 1-byte token' routine