; C02 library string.h02 assembly language subroutines
; Requires external routines SETSRC and SETDST
; Requires the following RAM locations be defined
; external zero page byte pairs SRCLO,SRCHI and DSTLO,DSTHI
; and external bytes TEMP0 and TEMP1

;Affects N,Z
;Returns A,Y = New String Length
STRAPD: STA TEMP0       ;Save Character to Append
        JSR STRLEN      ;Get Length of String
        BMI STRCLX      ;Return 255 if > 127
        LDA TEMP0       ;Restore Character to Append
STRAPL: STA (SRCLO),Y   ;Store at End of String
        BEQ STRLEX      ;Exit if NUL
        INY             ;Increment Past New Character
        LDA #0          ;Set Character to NUL
        BEQ STRAPL      ;and Append to String

;strcmp(&s) - Compare String (to Destination String)
;Requires: DSTLO, DSTHI - Pointer to destination string
;Args: X,Y = Pointer to source string
;Sets: SRCLO,SRCHI = Pointer to string 
;Affects N,Z
;Returns A=$01 and C=1 if Destination > Source  
;        A=$00 and Z=1, C=1 if Destination = Source  
;        A=$FF and C=0 if Destination < Source
;        Y=Position of first character that differs
STRCMP: JSR SETSRC      ;Initialize Source String
STRCML: LDA (DSTLO),Y   ;Load Destination Character
        CMP (SRCLO),Y   ;Compare Against Source Character
        BNE STRCMX      ;If Equal
        ORA (SRCLO),Y   ;  OR with Source Character
        BEQ STRCMR      ;  If Both are 0, Return 0
        INY             ;  Increment Offset
        BPL STRCML      ;    and Loop if < 128
STRCMX: BCC STRCLX      ;If Source < Destination, Return $FF & Carry Clear
        LDA #$01        ;Else Return 1 and Carry Set
STRCMR: RTS             ;  

;strchr(c, &s) - Find First Occurance of Character in String
;Args: A = Character to look for
;      X,Y = Pointer to string to search in
;Sets: SRCLO,SRCHI = Pointer to string 
;      TEMP3 = Character being searched for
;Affects: N,Z
;Returns: A = Position in string, C=1 if found
;         A = $FF, C=0 if not found
;         Y = Position of last character scanned
STRCHR: JSR SETSRC      ;Initialize Source String
STRCHA: STA TEMP3;      ;Save Search Character (alternate entry point)
STRCHL: LDA (SRCLO),Y   ;Get Next Character
        BEQ STRCLC      ;If NUL, Return $FF and Carry Clear 
        CMP TEMP3       ;Compare Character
        BEQ STRLEX      ;If Found, Return Index
        INY             ;Increment Counter and Loop if < 128
        BPL STRCHL      ;Else Return $FF and Carry Clear
STRCLC: CLC             ;Clear Carry
STRCLX: LDA #$FF        ;Load -1 into Accumulater
        RTS             ;and Return

;strapd(c, &s) - Append Character to String
;Args: A = Character to Append
;      X,Y = Pointer to String
;Sets: SRCLO, SRCHI - Pointer to String
;strlen(&s) - Return Length of String
;Args: X,Y - Pointer to string
;Sets: SRCLO,SRCHI = Pointer to source string
;Returns: A,Y = Length of string
;         N,Z based on A
STRLEN: JSR SETSRC      ;Initialize Source String
STRLEL: LDA (SRCLO),Y   ;Get Next Character
        BEQ STRLEX      ;If <> NUL 
        INY             ;  Increment Index
        BPL STRLEL      ;  and Loop if < 128
STRLEX: TYA             ;Transfer Index to Accumulator
        ORA #0          ;Set N and Z flags
        RTS             ;and Return

;strdst(&s) - Set Destination String 
;             Called before strcat(), strcmp(), strcpy(), strstr()
;Args: X,Y = Pointer to destination string
;Sets: SRCLO,SRCHI = Pointer to destination string
;Affects: N,Z
STRDST  EQU SETDST      ;Aliased to System Header function

;strcat(&s) Concatenate String (to Destination String)
;Requires: DSTLO, DSTHI - Pointer to destination string
;Args: X,Y = Pointer to source string
;Sets: SRCLO,SRCHI = Pointer to source string
;      TEMP3 = Length of source prior to concatenation
;Affects: C,N,Z
;Returns: A,Y = Total length of concatenated string
STRCAT: JSR SETSRC      ;Initialize Source String
STRCAL: LDA (DSTLO),Y   ;Find end of Destination String
        BEQ STRCAX      ;
        INY             ;
        BPL STRCAL      ;
STRCAX: STY TEMP3       ;Subtract Destination String Length
        LDA SRCLO       ;  from Source String Pointer
        SEC
        SBC TEMP3
        STA SRCLO
        LDA SRCHI
        SBC #$00
        STA SRCHI
        JMP STRCPL      ;Execute String Copy

;strcpy(&s) - Copy String (to Destination String)
;Requires: DSTLO, DSTHI - Pointer to destination string
;Args: X,Y = Pointer to source string
;Sets: SRCLO,SRCHI = Pointer to source string
;Affects: N,Z
;Returns: A,Y = Number of characters copied
STRCPA: LDY #0          ;Alternate entry point
        BEQ STRCPL      ;for when Source already set
STRCPY: JSR SETSRC      ;Initialize Source String
STRCPL: LDA (SRCLO),Y   ;Get Character from Source String
        STA (DSTLO),Y   ;Copy to Destination String
        BEQ STRCPX      ;If <> NUL 
        INY             ;  Increment Index
        BPL STRCPL      ;  and Loop if < 128
STRCPX: TYA             ;Transfer Index to Accumulator
        RTS             ;and Return

;strcut(n, &s) - Copy from Position n to End of Source (into Destination)
;Requires: DSTLO, DSTHI - Pointer to destination string
;Args: A = Starting position in start string
;      X,Y = Pointer to source string
;Sets: SRCLO,SRCHI = Pointer to specified position in source string
;Affects: N,Z
;Returns: A,Y = Length of copied string
STRCUT: JSR SETSRC      ;Initialize Source String
        CLC
        ADC SRCLO       ;Move Source Pointer
        STA SRCLO       ;  to Specified Position in String
        BCC STRCPL
        INC SRCHI
        JMP STRCPL      ;and Jump Into String Copy Loop

;strstr(&s) - Search for String (in Destination String)
;Requires: DSTLO, DSTHI - Pointer to destination string
;Args: X,Y = Pointer to search string
;Sets: DSTLO,DSTHI = Pointer to position in source string
;                    End of string if not found 
;      SRCLO,SRCHI = Pointer to source string
;      TEMP3 = Last position checked in destination string
;Affects: N,Z
;Returns: A = Position, C=1 if found
;         A = $FF, C=0 if not found
;         Y = Last position checked in source string      
STRSTR: JSR SETSRC      ;Initialize Source String
        STY TEMP3       ;Initialize Position
STRSTL: LDY #$00;       ;Initialize Compare Offset
        LDA (DSTLO),Y   ;Get Start Character in Destination
        BEQ STRCLC      ;If NUL return $FF and Carry Clear
        JSR STRCML      ;Jump into Compare Loop
        BEQ STRSTX      ;If Not Equal
        BMI STRSTN      ;  If Source is Greater
        LDA (SRCLO),Y   ;     If at End of Source String 
        BEQ STRSTX      ;     Return Current Position
STRSTN: INC TEMP3       ;  Else Increment Position
        BMI STRCLC      ;    If > 127 return $FF and Carry Clear
        INC DSTLO       ;    Increment Source Pointer
        BNE STRSTL
        INC DSTHI       ;    If not End of Memory
        BNE STRSTL      ;      Loop
        BEQ STRCLC      ;    Else return $FF and Carry Clear
STRSTX: SEC             ;Else Set Carry
        LDA TEMP3       ;  Load Position
        RTS             ;  and Return

;strrch(c, &s) - Find Last Occurance Character in String
;Args: A = Character to look for
;      X,Y = Pointer to string to search in
;Sets: SRCLO,SRCHI = Pointer to string 
;      TEMP3 = Character being searched for
;Affects: Y,C,N,Z
;Returns: A,X = Position of last occurance in string
;               $FF if not found
;         Y = Length of String
STRRCH: JSR SETSRC      ;Initialize Source String
        STA TEMP3;      ;Save Search Character (alternate entry point)
        LDX #$FF        ;Initialize Position
STRRCL: LDA (SRCLO),Y   ;Get Next Character
        BEQ STRRCX      ;If NUL, Exit with Position
        CMP TEMP3       ;Compare Character
        BNE STRRCS      ;If Found
        TYA             ;  Store Counter
        TAX
STRRCS: INY             ;Increment Counter
        BPL STRRCL      ;  and Loop if < 128
STRRCX: TXA             ;Copy Position to Accumulater
        RTS             ;  and Return