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875dd80998
AppleIIAsm-Collection/disks/disk5_strings/T.STRINGS.LIB
nathanriggs 875dd80998 stdio 0.2.0 updates 
- fixed a bunch of bugs
- separated common and stdio libraries
- commenting upgrades
- created min versions of each library
2018-12-14 21:23:32 -05:00

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*
JMP STRINGSX
*
*-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=*
* *
* STRINGS ROUTINE LIBRARY *
* *
* AUTHOR: NATHAN RIGGS *
* CONTACT: NATHAN.RIGGS@ *
* OUTLOOK.COM *
* *
* VERSION: 0.1.2 *
* DATE: 30-OCT-2018 *
* ASSEMBLER: MERLIN 8 PRO *
* *
* LICENSE: APACHE 2.0, WHERE *
* APPLICABLE. CODE INSPIRED *
* BY THE WORKS OF OTHERS MAY *
* FALL UNDER A DIFFERENT *
* LICENSE (NOTED IN ROUTINE). *
* *
* THIS IS A STANDARD LIBRARY *
* FOR STRING MANIPULATION. *
* STRINGS ARE MOSTLY JUST 1-D *
* ARRAYS PRECEDED BY A LENGTH *
* BYTE. THIS DIFFERS FROM THE *
* USE OF STRING IN THE PRINT *
* ROUTINES OF STDIO (THOUGH *
* NOT THE SINPUT ROUTINE) IN *
* THAT THOSE "STRINGS" ARE *
* TERMINATED WITH A #00 TO *
* INDICATE AN END, RATHER THAN *
* USING A LENGTH BYTE. *
* *
*------------------------------*
* *
* LIST OF ROUTINES *
* *
* STRCOMP : STRING COMPARE *
* STRCAT : CONCATENATE STRING *
* ASC2STR : NUL TO INDEXED STR *
* STR2ASC : INDEXED TO NUL STR *
* PRNSTR : PRINT STRING *
* NUM2STR : NUMBER TO STRING *
* STR2NUM : STRING TO NUMBER *
* *
*=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-*
*
*``````````````````````````````*
* STRCMP :: STRING COMPARE *
*- -*
* COMPARE TWO STRINGS AND *
* DETERMINE IF THEY ARE *
* IDENTICAL; IF NOT, DETERMINE *
* WHICH IS THE SHORTEST AND *
* WHICH IS THE LONGEST. *
* *
* Z FLAG = 1 IF IDENTICAL *
* Z FLAG = 0 IF NOT *
* CARRY = 1 IF STR2 > STR1 LEN *
* CARRY = 0 IF STR1 > STR2 LEN *
*- -*
* CLOBBERS: *
* *
* FLAGS: ????---- REG: AXYM *
*- -*
* CYCLES: ??? *
* SIZE: *
*- -*
* USAGE: *
* *
* LDA #>STR1 *
* PHA *
* LDA #<STR1 *
* PHA *
* LDA #>STR2 *
* PHA *
* LDA #<STR2 *
* PHA *
* JSR STRCMP *
* *
* STR1 STR "STRING1 " *
* STR2 STR "ZTRING2" *
*- -*
* ENTRY *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* STRING 2 ADDRESS LOW BYTE *
* STRING 2 ADDRESS HI BYTE *
* STRING 1 ADDRESS LOW BYTE *
* STRING 1 ADDRESS HI BYTE *
*- -*
* EXIT *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* *
* Y = LENGTH OF STRING 2 *
* X = LENGTH OF STRING 1 *
* A = CLOBBERED; TRASH *
* *
* - SEE DESCRIPTION FOR FLAG *
* CHANGES *
*- -*
* ADAPTED FROM LEVANTHAL AND *
* WINTHROP'S /6502 ASSEMBLY *
* LANGUAGE ROUTINES/. NOT *
* UNDER THE APACHE 2.0 LICENSE *
* AGREEMENT, SINCE THE BOOK *
* WAS WRITTEN BEFORE THE *
* LICENSE! *
* *
* THAT SAID, LEVENTHAL WROTE *
* THAT THE PURPOSE OF THE BOOK *
* WAS TO COPY THE SOURCE CODE, *
* AS REINVENTING THE WHEEL IS *
* TEDIOUS, AND HE PLACED NO *
* RESTRICTIONS ON ITS USE. *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
STRCMP
*
** SAVE RETURN ADDRESS
*
PLA
STA RETADR
PLA
STA RETADR+1
*
** GET PARAMETERS
*
PLA
STA ADDR2
PLA
STA ADDR2+1
PLA
STA ADDR1
PLA
STA ADDR1+1
*
LDY #0
LDA (ADDR1),Y ; GET LENGTH OF STRING 1
CMP (ADDR2),Y
BCC :BEGCMP ; IF STRING 2 IS SHORTER THEN
LDA (ADDR2),Y ; USE ITS LENGTH INSTEAD
*
** COMPARE THE STRINGS THROUGH THE
** LENGTH OF THE SHORTER STRING
*
:BEGCMP
TAX ; X IS LENGTH OF SHORTER STRING
BEQ :TSTLEN ; BR IF LENGTH IS 0
LDY #1 ; POINT AT FIRST CHAR OF STRINGS
:CMPLP
LDA (ADDR1),Y
CMP (ADDR2),Y
BNE :EXIT ; BR IF CHARS NOT EQUAL
; Z,C WILL BE PROPERLY SET
; OR CLEARED
; ELSE
INY ; NEXT CHAR
DEX ; DECREMENT COUNTER
BNE :CMPLP ; CONTINUE UNTIL ALL BYTES PAIRED
*
* THE 2 STRINGS ARE EQUAL TO LENGTH OF THE SHORTER
* SO USE LENGTHS AS BASIS FOR SETTING THE FLAGS
*
:TSTLEN
LDY #0 ; COMPARE LENGTHS
LDA (ADDR1),Y
CMP (ADDR2),Y ; SET OR CLEAR THE FLAGS
*
** Z FLAG = 1 IF STRINGS IDENTICAL
** Z FLAG = 0 IF NOT IDENTICAL
** CARRY = 0 IF STR2 LENGTH > STR1 LENGTH
** CARRY = 1 IF STR1 LENGTH >= STR2 LENGTH
*
:EXIT
*
** RESTORE RETURN ADDRESS
*
LDA RETADR+1
PHA
LDA RETADR
PHA
*
LDY #0
LDA (ADDR1),Y ; GET STR1 LENGTH
TAX ; RETURN IN X
LDA (ADDR2),Y ; STR2 LENGTH
TAY ; RETURN IN Y
*
RTS
*
*``````````````````````````````*
* STRCAT :: STRING CONCATENATE *
*- -*
* CONCATENATE TWO STRINGS INTO *
* A SINGLE STRING STORE WHERE *
* THE FIRST STRING IS LOCATED *
*- -*
* CLOBBERS: *
* *
* FLAGS: ????---- REG: AXYM *
*- -*
* CYCLES: ??? *
* SIZE: *
*- -*
* USAGE: *
* *
* LDA #>CATSTR *
* PHA *
* LDA #<CATSTR *
* PHA *
* LDA #>CATSTR2 *
* PHA *
* LDA #<CATSTR2 *
* PHA *
* LDA #7 ; MAX SIZE OF CAT *
* PHA *
* JSR STRCAT *
* *
* CATSTR STR "ABC" *
* BLANK STR " " *
* CATSTR2 STR "DEF" *
*- -*
* ENTRY *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* MAXIMUM LENGTH OF CONCAT STR *
* LOW BYTE OF STR2 ADDRESS *
* HIGH BYTE OF STR2 ADDRESS *
* LOW BYTE OF STR1 ADDRESS *
* HIGH BYTE OF STR1 ADDRESS *
*- -*
* EXIT *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* *
* Y = CLOBBERED; TRASH *
* X = LENGTH OF FINAL STRING *
* A = 1 OF OVERFLOW, 0 IF NO *
*- -*
* ADAPTED FROM LEVANTHAL AND *
* WINTHROP'S /6502 ASSEMBLY *
* LANGUAGE ROUTINES/. *
* AS SUCH, THIS MAY NOT FALL *
* UNDER THE APACHE 2.0 LICENSE *
* AGREEMENT, SINCE THE BOOK *
* WAS WRITTEN BEFORE THE *
* LICENSE! *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
STRCAT
*
** SAVE RETURN ADDRESS
*
PLA
STA RETADR
PLA
STA RETADR+1
*
** GET PARAMETERS
PLA
STA :MLEN ; MAXIMUM CONCAT LENGTH
*
PLA
STA ADDR2 ; STRING 1 ADDRESS
PLA ; IN ZERO PAGE
STA ADDR2+1
PLA
STA ADDR1 ; STRING 2 ADDRESS
PLA ; IN ZERO PAGE
STA ADDR1+1
*
** DETERMINE WHERE TO START
*
LDY #0
LDA (ADDR1),Y ; GET CUR LGTH OF S1, STORE
STA :S1LEN
STA :S1IND
INC :S1IND ; START CONCAT AT END OF S1
LDA (ADDR2),Y ; GET LENGTH OF S2, STORE
STA :S2LEN
LDA #1
STA :S2IND ; START CONCAT AT BEGIN OF S2
*
** DETERMINE NUMBER OF CHAR
*
LDA :S2LEN ; GET S2 LENGTH
CLC
ADC :S1LEN ; ADD TO LENGTH OF S1
STA :S3LEN ; STORE CONCAT LENGTH
BCS :TOOLONG ; BR IF LENGTH > 255
CMP :MLEN ; CHECK AGAINST MAX LENGTH
BEQ :LENOK ; BR IF LENGTH < MAX
BCC :LENOK
*
** RESULTING STRING WILL BE TOO LONG SO
** INDICATE A STRING OVERFLOW, __SOVF = 0FF
** SET NUMBER OF CHARS TO CONCAT = MLEN - S1LEN
** SET LENGTH OF STRING 1 TO MAX LENGTH
*
:TOOLONG
LDA #$0FF
STA :SOVF ; INDICATE OVERFLOW
LDA :MLEN
SEC
SBC :S1LEN
BCC :EXIT
; EXIT IF MLEN < S1LEN
STA :SCNT ; ORIG STR WAS TOO LONG
LDA :MLEN
STA :S1LEN ; SET STR1 LENGTH TO MAX
JMP :DOCAT
*
** RESULTING LENGTH DOES NOT EXCEED MAX
** LENGTH OF STRING 1 = S1LEN + S2LEN
** INDICATE NO OVERFLOW, __SOVF = 0
** SET NUM OF CHARS TO CONCAT TO LENGTH OF STR 2
*
:LENOK
STA :S1LEN
LDA #0 ; SAVE SUM OF 2 LENGTHS
STA :SOVF ; INDICATE NO OVERFLOW
LDA :S2LEN
STA :SCNT ; COUNT = LENGTH OF STRING 2
*
** CONCAT STRINGS
*
:DOCAT
LDA :SCNT
BEQ :EXIT ; EXIT IF NO BYTES LEFT
*
:CATLP
LDY :S2IND
LDA (ADDR2),Y ; GET NEXT BYTE FROM S2
LDY :S1IND
STA (ADDR1),Y ; MOVE IT TO END OF STR 1
INC :S1IND ;INC STRING 1 INDEX
INC :S2IND ; INC STRING 2 INDEX
DEC :SCNT ; DECREMENT COUNTER
BNE :CATLP ; CONT UNTIL __SCNT = 0
*
*
:EXIT
*
** RESTORE RETURN ADDRESS
*
LDA RETADR+1
PHA
LDA RETADR
PHA
*
LDA :S1LEN
LDY #0
STA (ADDR1),Y
LDA :SOVF
ROR A ; CARRY = 1 IF OVERFLOW, 0 IF NOT
LDX :S3LEN ; RETURN FINAL LENGTH
*
RTS
*
** DATA
*
:S3LEN DS 1
:S1LEN DS 1
:S1IND DS 1
:S2LEN DS 1
:S2IND DS 1
:MLEN DS 1
:SCNT DS 1
:SOVF DS 1
*
*``````````````````````````````*
* PRNSTR :: PRINT INDEXED STR *
*- -*
* PRINT A STRING WITH LENGTH *
* THAT PRECEDES START OF STR *
*- -*
* CLOBBERS: *
* *
* FLAGS: ????---- REG: AXYM *
*- -*
* CYCLES: ??? *
* SIZE: *
*- -*
* USAGE: *
* *
* LDA #>STR ; STRING ADDRESS *
* PHA *
* LDA #<STR *
* PHA *
* JSR PRNSTR *
*- -*
* ENTRY *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* LOW BYTE OF STRING ADDRESS *
* HIGH BYTE OF STRING ADDRESS *
*- -*
* EXIT *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* *
* Y = LOW BYTE STRING ADDR *
* X = HI BYTE STRING ADDR *
* A = STRING LENGTH *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
PRNSTR
*
** SAVE RETURN ADDRESS
*
PLA
STA RETADR
PLA
STA RETADR+1
*
** GET PARAMETERS
*
PLA
STA ADDR1 ; ADDRESS OF STRING
PLA
STA ADDR1+1
*
LDY #0
LDA (ADDR1),Y ; GET STRING LENGTH
STA :S1LEN
:LP
INY
LDA (ADDR1),Y ; GET CHARACTER
JSR SCOUT1 ; PRINT CHARACTER TO SCREEN
CPY :S1LEN ; IF Y < LENGTH
BNE :LP
; LOOP; ELSE
LDY #0
LDA (ADDR1),Y
*
** RESTORE RETURN ADDRESS
*
LDA RETADR+1
PHA
LDA RETADR
PHA
*
LDY #0
LDA (ADDR1),Y ; STRING LENGTH IN A
LDY ADDR1
LDX ADDR1+1 ; ADDRESS IN Y,X
*
RTS
*
** DATA
*
:S1LEN DS 1
*
*``````````````````````````````*
* NUM2STR :: NUMBER TO STRING *
*- -*
* CONVERTS A 16-BIT NUMBER TO *
* ITS STRING EQUIVALENT. *
*- -*
* CLOBBERS: *
* *
* FLAGS: ????---- REG: AXYM *
*- -*
* CYCLES: ??? *
* SIZE: *
*- -*
* USAGE: *
* *
* LDA #>$300 ; DESTINATION *
* PHA *
* LDA #<$300 *
* PHA *
* LDA #>11111 ; VALUE TO *
* PHA ; CONVERT *
* LDA #<11111 *
* PHA *
* JSR NUM2STR *
*- -*
* ENTRY *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* LO BYTE DESTINATION ADDRESS *
* HI BYTE DESTINATION ADDRESS *
* LO BYTE VALUE TO CONVERT *
* HI BYTE VALUE TO CONVERT *
*- -*
* EXIT *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* *
* Y = COUNTER; TRASH *
* X = COUNTER; TRASH *
* A = LOW BYTE OF RET ADDR *
*- -*
* ADAPTED FROM LEVANTHAL AND *
* WINTHROP'S /6502 ASSEMBLY *
* LANGUAGE ROUTINES/. *
* AS SUCH, THIS MAY NOT FALL *
* UNDER THE APACHE 2.0 LICENSE *
* AGREEMENT, SINCE THE BOOK *
* WAS WRITTEN BEFORE THE *
* LICENSE! *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
NUM2STR
*
** SAVE RETURN ADDRESS
*
PLA
STA RETADR
PLA
STA RETADR+1
*
** GET PARAMETERS
*
PLA
STA :VALSTR
PLA
STA :VALSTR+1
*
STA :NGFLAG
BPL :GETBP ; BR IF VAL IS POS
LDA #0
SEC
SBC :VALSTR
STA :VALSTR
LDA #0
SBC :VALSTR+1
STA :VALSTR+1
*
:GETBP
PLA
STA ADDR1 ; ADDRESS TO STORE STRING
PLA
STA ADDR1+1
LDA #0 ; SET BUFFER TO EMPTY
LDY #0
STA (ADDR1),Y ; BUFFER(0) = 0
*
** CONVERT VAL TO STRING
*
:CNVERT
*
** VALUE = VALUE DIV 10
** MOD10 = VALUE MOD 10
*
LDA #0
STA :MOD10
STA :MOD10+1
LDX #16
CLC ; CLEAR CARRY
*
:DVLOOP
ROL :VALSTR ; SHIFT CARRY INTO DIVBIT 0
ROL :VALSTR+1 ; WHICH WILL BE THE QUOTIENT
ROL :MOD10 ; + SHIFT DIV AT SAME TIME
ROL :MOD10+1
*
** A,Y = DIVIDEND - DIVISOR
*
SEC
LDA :MOD10
SBC #10
TAY ; SAVE LOWB IN REG Y
LDA :MOD10+1
SBC #0 ; SUBTRACT CARRY
BCC :DECCNT ; BR IF DEND < DIVISOR
STY :MOD10 ; ELSE
STA :MOD10+1 ; NXT BIT OF Q IS A ONE AND SET
; DIVIDEND = DEND - DIVISOR
:DECCNT
DEX
BNE :DVLOOP
ROL :VALSTR ; SHIFT IN LAST CARRY FOR Q
ROL :VALSTR+1
*
** CONCAT NEXT CHAR
*
:CONCH
LDA :MOD10
CLC
ADC #$B0
*
** ADC #'0' ; CONVERT 0..9 TO ASCII 0-9
*
JSR :CONCAT
*
** IF VALUE <> 0 THEN CONTINUE
*
LDA :VALSTR
ORA :VALSTR+1
BNE :CNVERT ; BR IF VALUE != 0
*
:EXIT
LDA :NGFLAG
BPL :POS ; BR IF ORIG VAL POS
LDA #'-' ; ELSE
JSR :CONCAT ; PUT A MINUS SIGN IN FRONT
*
:POS
*
** RESTORE RETURN ADDRESS
*
LDA RETADR+1
PHA
LDA RETADR
PHA
*
RTS ; RETURN
*
********************************
* CONCAT SUBROUTINE
********************************
*
:CONCAT
PHA ; SAVE CHAR ON STACK
*
** MOVE BUFFER RIGHT ONE CHAR
*
LDY #0
LDA (ADDR1),Y ; GET CURRENT LENGTH
TAY
BEQ :EXITMR ; BR IF LENGTH=0
*
:MVELP
LDA (ADDR1),Y ; GET NEXT CHAR
INY
STA (ADDR1),Y ; STORE IT
DEY
DEY
BNE :MVELP ; CONT UNTIL DONE
*
:EXITMR
PLA ; GET CHAR BACK FROM STACK
LDY #1
STA (ADDR1),Y ; STORE THE CHAR
LDY #0
LDA (ADDR1),Y ; GET LENGTH BYTE
CLC
ADC #1 ; INC LENGTH BY ONE
STA (ADDR1),Y ; UPDATE LENGTH
*
RTS
*
** DATA
*
:NGFLAG DS 1
:VALSTR DS 2
:MOD10 DS 2
*
*``````````````````````````````*
* STR2NUM :: STRING TO NUMBER *
*- -*
* CONVERTS A STRING TO THE *
* EQUIVALENT 16BIT NUMBER. *
*- -*
* CLOBBERS: *
* *
* FLAGS: ????---- REG: AXYM *
*- -*
* CYCLES: ??? *
* SIZE: *
*- -*
* USAGE: *
* *
* LDA #>$300 ; STRING ADDR *
* PHA *
* LDA #<$300 *
* PHA *
* JSR STR2NUM *
*- -*
* ENTRY *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* LO BYTE OF STRING ADDRESS *
* HI BYTE OF STRING ADDRESS *
*- -*
* EXIT *
* *
* TOP OF STACK *
* *
* LOW BYTE OF RETURN ADDRESS *
* HI BYTE OF RETURN ADDRESS *
* *
* Y = HI BYTE OF NUMBER *
* X = LO BYTE OF NUMBER *
* A = LOW BYTE OF RET ADDR *
*- -*
* ADAPTED FROM LEVANTHAL AND *
* WINTHROP'S /6502 ASSEMBLY *
* LANGUAGE ROUTINES/. *
* AS SUCH, THIS MAY NOT FALL *
* UNDER THE APACHE 2.0 LICENSE *
* AGREEMENT, SINCE THE BOOK *
* WAS WRITTEN BEFORE THE *
* LICENSE! *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
*
STR2NUM
*
** SAVE RETURN ADDRESS
*
PLA
STA RETADR
PLA
STA RETADR+1
*
** GET PARAMETERS
*
PLA
STA ADDR1 ; ADRESS OF STRING
PLA ; TO CNVERT
STA ADDR1+1
*
** INITIALIZE
*
LDY #0
LDA (ADDR1),Y
TAX ; GET LENGITH; TO REGX
LDA #1
STA :NINDEX ; INDEX = 1
LDA #0
STA :NACCUM ; ACCUM = 0
STA :NACCUM+1
STA :SNGFLAG ; SIGN IS POSITIVE
*
** CHECK THAT BUFFER IS NOT ZERO
*
TXA
BNE :INIT1 ; EXIT WITH ACCUM = 0
; IF BUFFER IS EMPTY
JMP :EREXIT ; ERROR EXIT IF NOTHING
; IN BUFFER
:INIT1
LDY :NINDEX
LDA (ADDR1),Y
CMP #'-'
BNE :PLUS ; BR IF NOT -
LDA #$0FF
STA :SNGFLAG ; ELSE SIGN IS NEGATIVE
INC :NINDEX
DEX ; DECREMENT COUNT
BEQ :EREXIT ; ERROR EXIT IF ONLY
; - IN BUFFER
JMP :CNVERT
:PLUS
CMP #'+'
BNE :CHKDIG ; START CONVERSION IF 1ST
; CHARACTER IS NOT A +
INC :NINDEX
DEX ; DEC COUNT; IGNORE + SIGN
BEQ :EREXIT ; ERROR EXIT IF ONLY
; + IN THE BUFFER
:CNVERT
LDY :NINDEX
LDA (ADDR1),Y
; GET NEXT CHAR
:CHKDIG
CMP #$B0 ; "0"
BMI :EREXIT ; ERROR IF NOT A NUMERAL
CMP #$BA ; '9'+1; TECHNICALLY :
BPL :EREXIT ; ERR IF > 9 (NOT NUMERAL)
PHA ; PUSH DIGIT TO STACK
*
** VALID DECIMAL DIGIT SO
** ACCUM = ACCUM * 10
** = * (8+2)
** = (ACCUM * 8) + (ACCUM * 2)
*
ASL :NACCUM
ROL :NACCUM+1 ; TIMES 2
LDA :NACCUM
LDY :NACCUM+1 ; SAVE ACCUM * 2
ASL :NACCUM
ROL :NACCUM+1
ASL :NACCUM
ROL :NACCUM+1 ; TIMES 8
CLC
ADC :NACCUM ; SUM WITH * 2
STA :NACCUM
TYA
ADC :NACCUM+1
STA :NACCUM+1 ; ACCUM=ACCUM * 10
*
** ADD IN THE NEXT DIGIT
** ACCUM = ACCUM + DIGIT
*
PLA ; GET THE DIGIT NACK
SEC
SBC #$B0
CLC ; CONVERT STR TO BIN
ADC :NACCUM
STA :NACCUM
BCC :D2B1 ; BRANCH IF NO CARRY TO HBYTE
INC :NACCUM+1 ; ELSE INC HIGH BYTE
:D2B1
INC :NINDEX ;INC TO NEXT CHARACTER
DEX
BNE :CNVERT ; CONTINUE CONVERSION
LDA :SNGFLAG
BPL :OKEXIT ; BR IF VAL IS POSITIVE
LDA #0 ; ELSE REPLACE WITH -RESULT
SEC
SBC :NACCUM
STA :NACCUM
LDA #0
SBC :NACCUM+1
STA :NACCUM+1
*
** GET THE BINARY VALUE AND RETURN
*
:OKEXIT
CLC
BCC :EXIT
:EREXIT
SEC
:EXIT
; Y IS ALREADY LOW BYTE
*
** RESTORE RETURN ADDRESS
*
LDA RETADR+1
PHA
LDA RETADR
PHA
*
LDX :NACCUM+1
LDY :NACCUM
LDA :NINDEX
*
RTS
*
** DATA
*
:NACCUM DS 2
:SNGFLAG DS 1
:NINDEX DS 1
*
STRINGSX
*
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