The BBC and Master Computer Public Domain Library

B8B6 INPUT

Submitted by Steve Fewell

Description:

Check the next non-space character. If it's a '#' then jump to the PRINT# routine [&B847].

If the next character is a 'LINE' keyword token then set the carry flag; otherwise, decrement BASIC Text Pointer A
Offset (&0A), as we do not need the next character yet, and clear the carry flag.
Set bit 6 of location &4C to the value of the carry flag [by setting the top bit & shifting right one position].
Set &4D to #&FF (field extraction offset flag, #&FF if not currently extracting fields from the Input String).

[&B8CA] Call routine &9299, which does the following:

* Get the next non-space character.

* Call routine &927A to process any ' [quote], TAB( and SPC special print characters

* If carry is clear on return from routine &927A, then a special function was carried out (either New line, TAB(
or SPC), so exit routine.

* If next character is not " [double-quote] then a String is not present, so set the carry flag and exit.

* Otherwise, we need to extract and output the String value, as follows:

*    [&92A5] Get next character.

*    If next character is <cr> [carriage return] then issue 'Missing "' error [as a closing double quote
wasn't present before the end of the statement line.

*    If the next character is a double quote and the characer after it is not then clear carry, set BASIC
Text Pointer A to BASIC Text Pointer B location and exit, as we have outputted the string value. Otherwise, we need to
output a single double quote character (as two double quotes were found inside the string value).

*    Call routine &BD98 to output the character.

*    Jump back to &92A5 to get next character of the string.

If the carry flag is clear on return from routine &9299, then a special character was found & processed, so keep
calling routine &9299 to check for further special operations (i.e. New line ('), TAB(, SPC or String (")), until
the carry flag is set (indicating that no further special characters were found); Set &4D to #&FF & clear carry flag
(as special characters terminate a field extraction).

[&B8D9] Shift byte &4C (the LINE-status byte) left 1-position (so that the top bit is set if we are in 'LINE'-mode)
(the processor flags are temporarily saved while this is done). This also removes the previous Top-bit setting (special
character) of &4C. Shift the carry flag into the top byte of &4C (moving the 'LINE'-mode flag right a position,
again). (The carry flag is clear if special characters were not found, or set if special characters were found).
So, now Bit 7 of &4C is clear if special PRINT characters (',",TAB(,SPC) were processed, and Bit 6 is set if were are
in 'LINE'-mode.

If the next character is "," or ";", then jump back to &B8CA to check for, and process, and special characters
after the field separator.
[Note: If special characters were found after the last ',' or ';', then a '?'-prompt is not output; also, additional
fields cannot be extracted from a previous input entry for any additional variables supplied - instead, the user will be
prompted for another entry value]

Next, we should either have a variable or the end of the statement, as we have processed all valid characters that can precede
a variable in an INPUT statement, namely: double quote ("), Comma (,), Semi-Colon (;), SPC, TAB( and quote (').
Decrement BASIC Text pointer A offset (so that the variable name starts at the next character, rather than the current one).
Save bytes &4C and &4D to the stack.
Call routine &98AE to evaluate the variable name (and create it if the variable doesn't already exist and isn't a
direct memory access (!x, ?x, $x).
If the zero flag is set on return from &98AE, then a variable was not specified, so retrieve the 2-bytes pushed to
the stack and jump to &9002 (to continue to the next statement if end of statement was found; otherwise, issue a
Syntax error).

Retrieve bytes &4C and &4D from the stack.
Call routine &9275 to Set BASIC Text pointer A offset to BASIC Text pointer B offset.
Store the processor flags to the stack (this stores whether the variable is a String or not).
if bit 6 of &4C is clear (i.e. we are not in LINE mode), and &4D location is not #&FF (i.e. not first field)
then jump to &B91F (to extract the next field).
If the top bit of &4C is set (Special characters were not found after the last field break), then output a
'?'-character - this is the default user input prompt.

Call routine &BA70 to get the user's input, as follows:

* Set &38 to 6 and zero &37. This is the address to place the user's input entry: &0600 (The SWA).

[Note: If called from &BA74, the address to place the user's input entry is &0700 (The Command Line)].

* Set &39 to #&EE. This is the maximum input line length.

* Set &3A to #&20 and &3B to #&FF. These are the minimum and maximum characters.

* Set Y to #&00 (parameter block MSB), X to #&37 (parameter block LSB).

* Set A to #&00 (OSWORD call 0 - get input characters from current device).

* Call OSWORD (&FFF1) with A = 0 and the parameter block data in locatons &0037 - &003B.

* If the carry flag is set after OSWORD call (with A = 0), then Escape was pressed, so generate an 'Escape' error;
otherwise, all is ok, so zero COUNT (&1E) and exit the &BA70 routine.

Store Y (the length of the input field) in &36 (SWA length field).
Clear the top bit of &4C (the special characters not found flag).

If bit 6 of &4C is clear (i.e. we are not in LINE mode), then fields are separated by commas (etc...), so:

* [B91F] Set &1B (the current SWA offset) to A (this is 0 for the first field, & &4D for other fields).

* Zero &19 and set &1A to #&06 (So that &19-&1A is a Pointer to the SWA value).

* Call routine &ACF8 to Extract the next field from the SWA (& place it in the SWA starting at location &0600)

* Call routine &8EEB to Get the next non-space character and compare with ",".

* If comma not found (then <cr> found [if not <cr> get next char until ',' or <cr>] - end of input entry (SWA)); so,
set Y to #&FE (Next statement will increment this to #&FF - indicating that we are no longer extracting fields
from the input line).

* Increment Y (SWA offset) [This equals #&FF when we are not extracting fields from the SWA] and store Y in &4D.

Retrieve the processor flags from the stack.

If the variable is an Integer (carry flag clear) then set the variable as follows:

* [&B93B] Call routine &BC43 to store the variable address & type details (&2A,&2B,&2C) on the 6502 stack.

* Call ASCII to Numeric conversion routine (ASCNUM, &AB4E) to convert SWA string value to a binary number.

* Call routine &B32B to set the numeric variable to the numeric value (which is either a Floating-Point or Integer
value)

* Jump back to &B8CA to check for further variables or special characters on the INPUT statement.

If the variable is a String (carry flag set) then set the variable as follows:

* [&B946] Zero &27 - (Set current result type to String).

* Call routine &90AE to Set the String variable to the SWA value.

* Jump back to &B8CA to check for further variables or special characters on the INPUT statement.

Disassembly for the INPUT routine

B8B2	h	104	68	PLA
B8B3	h	104	68	PLA
B8B4		128 142	80 8E	BRA -114 --> &B844 [JMP &9002] check end of statement & process next program statement
B8B6		032 223 140	20 DF 8C	JSR &8CDF Get next non-space char (PTR A) and compare with '#'
B8B9		240 140	F0 8C	BEQ -116 --> &B847 PRINT#
B8BB		201 134	C9 86	CMP#&86 'LINE'-token
B8BD		240 003	F0 03	BEQ 3 --> &B8C2
B8BF		198 010	C6 0A	DEC &0A
B8C1		024	18	CLC
B8C2	fL	102 076	66 4C	ROR &4C
B8C4	FL	070 076	46 4C	LSR &4C
B8C6		169 255	A9 FF	LDA#&FF
B8C8	M	133 077	85 4D	STA &4D
B8CA		032 153 146	20 99 92	JSR &9299
B8CD		176 010	B0 0A	BCS 10 --> &B8D9
B8CF		032 153 146	20 99 92	JSR &9299
B8D2		144 251	90 FB	BCC -5 --> &B8CF
B8D4		162 255	A2 FF	LDX#&FF
B8D6	M	134 077	86 4D	STX &4D
B8D8		024	18	CLC
B8D9		008	08	PHP
B8DA	L	006 076	06 4C	ASL &4C
B8DC	(	040	28	PLP
B8DD	fL	102 076	66 4C	ROR &4C
B8DF	,	201 044	C9 2C	CMP#&2C ','
B8E1		240 231	F0 E7	BEQ -25 --> &B8CA
B8E3	;	201 059	C9 3B	CMP#&3B ';'
B8E5		240 227	F0 E3	BEQ -29 --> &B8CA
B8E7		198 010	C6 0A	DEC &0A
B8E9	L	165 076	A5 4C	LDA &4C
B8EB	H	072	48	PHA
B8EC	M	165 077	A5 4D	LDA &4D
B8EE	H	072	48	PHA
B8EF		032 174 152	20 AE 98	JSR &98AE Evaluate variable name & create if new variable
B8F2		240 190	F0 BE	BEQ -66 --> &B8B2 exit & process next statement
B8F4	h	104	68	PLA
B8F5	M	133 077	85 4D	STA &4D
B8F7	h	104	68	PLA
B8F8	L	133 076	85 4C	STA &4C
B8FA	u	032 117 146	20 75 92	JSR &9275 PTR A Offset = PTR B offset
B8FD		008	08	PHP
B8FE	$L	036 076	24 4C	BIT &4C
B900	p	112 006	70 06	BVS 6 --> &B908
B902	M	165 077	A5 4D	LDA &4D
B904		201 255	C9 FF	CMP#&FF
B906		208 023	D0 17	BNE 23 --> &B91F
B908	$L	036 076	24 4C	BIT &4C
B90A		016 005	10 05	BPL 5 --> &B911
B90C	?	169 063	A9 3F	LDA#&3F '?'
B90E		032 238 255	20 EE FF	JSR &FFEE OSBYTE
B911	p	032 112 186	20 70 BA	JSR &BA70
B914	6	132 054	84 36	STY &36
B916	L	006 076	06 4C	ASL &4C
B918		024	18	CLC
B919	fL	102 076	66 4C	ROR &4C
B91B	$L	036 076	24 4C	BIT &4C
B91D	p	112 025	70 19	BVS 25 --> &B938
B91F		133 027	85 1B	STA &1B
B921	d	100 025	64 19	STZ &19
B923		169 006	A9 06	LDA#&06
B925		133 026	85 1A	STA &1A
B927		032 248 172	20 F8 AC	JSR &ACF8 Extract next field (PTR B)
B92A		032 235 142	20 EB 8E	JSR &8EEB Get next non-space char (PTR B) & compare with ','
B92D		240 006	F0 06	BEQ 6 --> &B935
B92F		201 013	C9 0D	CMP#&0D
B931		208 247	D0 F7	BNE -9 --> &B92A
B933		160 254	A0 FE	LDY#&FE
B935		200	C8	INY
B936	M	132 077	84 4D	STY &4D
B938	(	040	28	PLP
B939		176 011	B0 0B	BCS 11 --> &B946
B93B	C	032 067 188	20 43 BC	JSR &BC43 Push &2A, &2B & &2C to the 6502 Stack
B93E	N	032 078 171	20 4E AB	JSR &AB4E ASCNUM (Convert ASCII String to Numeric value)
B941	+	032 043 179	20 2B B3	JSR &B32B Set numeric variable
B944		128 132	80 84	BRA -124 --> &B8CA
B946	d'	100 039	64 27	STZ &27
B948		032 174 144	20 AE 90	JSR &90AE Set String variable
B94B		128 247	80 F7	BRA -9 --> &B944

9299

9299		032 224 142	20 E0 8E	JSR &8EE0 Get next non-space char (PTR A)
929C	z	032 122 146	20 7A 92	JSR &927A Check for "'", 'TAB(' or 'SPC'
929F		144 242	90 F2	BCC -14 --> &9293 [RTS]
92A1	"	201 034	C9 22	CMP#&22
92A3		208 237	D0 ED	BNE -19 --> &9292 [SEC : RTS]
92A5		200	C8	INY
92A6		177 025	B1 19	LDA (&19),Y
92A8		201 013	C9 0D	CMP#&0D
92AA		240 232	F0 E8	BEQ -24 --> &9294 'Missing "' error
92AC	"	201 034	C9 22	CMP#&22
92AE		208 009	D0 09	BNE 9 --> &92B9
92B0		200	C8	INY
92B1		132 027	84 1B	STY &1B
92B3		177 025	B1 19	LDA (&19),Y
92B5	"	201 034	C9 22	CMP#&22
92B7		208 177	D0 B1	BNE -79 --> &926A Clear carry flag, Set PTR A offset = PTR B offset & exit
92B9		032 152 189	20 98 BD	JSR &BD98 Output character in A
92BC		128 231	80 E7	BRA -25 --> &92A5

BA70 Prompt for and get the user's input line

BA70		169 006	A9 06	LDA#&06
BA72		128 002	80 02	BRA 2 --> &BA76
BA74		169 007	A9 07	LDA#&07
BA76	d7	100 055	64 37	STZ &37
BA78	8	133 056	85 38	STA &38
BA7A		169 238	A9 EE	LDA#&EE
BA7C	9	133 057	85 39	STA &39
BA7E		169 032	A9 20	LDA#&20
BA80	:	133 058	85 3A	STA &3A
BA82		160 255	A0 FF	LDY#&FF
BA84	;	132 059	84 3B	STY &3B
BA86		200	C8	INY
BA87	7	162 055	A2 37	LDX#&37
BA89		152	98	TYA
BA8A		032 241 255	20 F1 FF	JSR &FFF1 OSWORD
BA8D		144 006	90 06	BCC 6 --> &BA95 Zero COUNT (&1E) and exit routine
BA8F	L}	076 125 155	4C 7D 9B	JMP &9B7D Escape error

 

---

  Or