The BBC and Master Computer Public Domain Library

9241 (PRINT) TAB(

Submitted by Steve Fewell

Description:

Get the Integer result of the expression after the 'TAB(' keyword.
If the result is a Float then convert it to an Integer, if the result is a string then generate 'Type mismatch' error.

Get the next non-space character, if it is a "," then the TAB function call has two arguments so jump to &922D to do the following:: * Push the first argument (&2A) to the Stack.; * Get the Integer result of the expression after the ','. If the result is a Floating-Point value then convert to an Integer,
if the result is a string then generate 'Type mismatch' error.; * If the next non-space character is not ')' then generate 'Missing )' error.; * Send #&1F to the Operating System output character routine (&FFEE) to start a VDU 31 command.; * Pop the first argument from the stack and send it to the Operating System output character routine (&FFEE).; * Call routine &9840 to send &2A (the second argument) to the Operating System output character vector (&020E).; * Now, the cursor should be in the required position (as VDU 31 command with 2 arguments moves the cursor to
the specified location).; * Jump to &926A: (Clear carry, Set PTR A Offset to PTR B Offset & exit (back to the PRINT routine).

Otherwise, the TAB function has only one argument so continue with &9249 and do the following:: * Check whether next character is a ')', if it isn't then generate 'Missing ,' error.; * Subtract COUNT (&1E) from the 1-byte Integer result (&2A).; * If the subtraction result is zero then jump to &926A: (Clear carry, Set &0A (PTR A Offset) to &1B (PTR B Offset)
and exit (back to the PRINT routine).; * If the subtraction result was positive (carry flag still set) then set X to the subtraction result and
jump to &9262 to output X number of spaces (and then Clear carry, Set &0A (PTR A Offset) to &1B (PTR B Offset),
and exit (back to the PRINT routine).; * If the subtraction result was negative (carry flag is clear) then call &BA92 to output a new line and set
COUNT (&1E) to zero and jump to &925E to Set X to &2A and output X number of spaces (and then Clear carry,
Set &0A (PTR A Offset) to &1B (PTR B Offset), and exit (back to the PRINT routine).

Disassembly for the (PRINT) TAB( routine

922A	L	076 246 142	4C F6 8E	JMP &8EF6 'Missing ,' error
922D	*	165 042	A5 2A	LDA &2A
922F	H	072	48	PHA
9230		032 167 150	20 A7 96	JSR &96A7 Extract Integer result of expression and check for closing bracket
9233		169 031	A9 1F	LDA#&1F
9235		032 238 255	20 EE FF	JSR &FFEE OSWRCH (Write character)
9238	h	104	68	PLA
9239		032 238 255	20 EE FF	JSR &FFEE OSWRCH (Write character)
923C	@	032 064 152	20 40 98	JSR &9840 Send ?&2A to the OS output vector
923F	)	128 041	80 29	BRA 41 --> &926A Clear carry flag, Set PTR A offset = PTR B offset and exit
9241		032 175 150	20 AF 96	JSR &96AF Get Integer result of expression
9244		032 235 142	20 EB 8E	JSR &8EEB Get next non-space character (PTR B) and compare with ','
9247		240 228	F0 E4	BEQ -28 --> &922D
9249	)	201 041	C9 29	CMP#&29 ')'
924B		208 221	D0 DD	BNE -35 --> &922A
924D	*	165 042	A5 2A	LDA &2A
924F		229 030	E5 1E	SBC &1E (COUNT)
9251		240 023	F0 17	BEQ 23 --> &926A Clear carry flag, Set PTR A offset = PTR B offset and exit
9253		170	AA	TAX
9254		176 012	B0 0C	BCS 12 --> &9262 Output X number of spaces, clr carry, PTR A=PTR B & exit
9256		032 146 186	20 92 BA	JSR &BA92 Start new output line
9259		128 003	80 03	BRA 3 --> &925E Output ?&2A number of spaces, clr carry, PTR A=PTR B & exit

9840 Send character in ?&2A to the Output vector

9840	*	165 042	A5 2A	LDA &2A
9842	l	108 014 002	6C 0E 02	JMP (&020E) OS Output character vector (WRCHV)