6502-OS/util/string-conversion.s65

.include "string.h65"
.include "math.h65"
Export str,hex_char_to_uint8, hex_str_to_uint, uint8_to_hex_str

.code
;
; FROM STRING
;;********************************************************************************
;; @function Convert a hex char into a binary number
;; @details
;;  The char must be one of [0-9,a-f,A-F].
;;  All results are only valid if N == 0.
;; @param A: Char to convert
;; @returns C: 0 == success, 1 == invalid char
;; @returns A: The converted number
;;********************************************************************************
.proc hex_char_to_uint8
    sec
    sbc #'0'
    bmi @invalid  ; char was in [0, '0')
    cmp #10
    bcc @rts  ; A in [0, 10)
    ; char higher than '9'
    sbc #('A' - '0')
    bmi @invalid  ; char was in ('0', 'A')
    cmp #7
    bcc @hex_char  ; A in [0, 6]
    ; char higher than 'F'
    sbc #('a' - 'A')
    bmi @invalid  ; char was in ('F', 'a')
    cmp #17
    bcc @hex_char  ; A in [0, 6]
    ; char was in ('f', $ff]
@invalid:
    sec
    rts
@hex_char:
    ; carry is not set
    adc #10
@rts:
    rts
.endproc


;;********************************************************************************
;; @function Convert a number encoded as hexadecimal string to a binary number
;; @details
;;  The string must only consist of [0-9,a-f,A-F].
;;  All results are only valid if C == 0.
;; @param ARG0-1: Address of string
;; @param A: Number of chars to convert
;; @param Y: Offset onto string so that first char = (ARG0) + Y
;; @returns C: 0 => success, 1 => invalid string
;; @returns A: 0
;; @returns X: Size of the number in bytes
;; @returns Y: Offset onto string, one past the end of the number
;; @returns ARG2-...: Number in big endian
;; @modifies X,Y,A
;;********************************************************************************
.proc hex_str_to_uint
    ldx #0
    cmp #0  ; check if accumulator is zero
    beq @rts_clc
    bit #%00000001  ; check if accumulator is even
    beq @loop  ; even
    ; not even
    stz ARG2
    inc  ; later subtract 2
    pha
    bra @less_sig_char
@loop:
    pha
        ; more significant char
        lda (ARG0),y  ; load next char
        iny
        jsr hex_char_to_uint8
        bcs @invalid_pla
        rol
        rol
        rol
        rol
        sta ARG2,x
@less_sig_char:
        ; less significant char
        lda (ARG0),y  ; load next char
        iny
        jsr hex_char_to_uint8
        bcs @invalid_pla
        ora ARG2,x
        sta ARG2,x
        inx
    pla
    dec
    dec
    bne @loop
    rts
@invalid_pla:   ; carry must be set
    pla     ; doesnt update the carry
@invalid:
    rts
@rts_clc:
    clc
    rts
.endproc


;
; TO STRING
;


;;********************************************************************************
;; @function Convert a 1 byte number into two hex characters
;; @param A: Number to convert
;; @returns A: Most significant digit
;; @returns X: Least significant digit
;; @modifies A,X,Y
;;********************************************************************************
.proc uint8_to_hex_str
    pha
    and #%00001111
    tay
    ldx HEX_CHARS_UPPER,y
    pla
    div A,16
    and #%00001111
    tay
    lda HEX_CHARS_UPPER,y
    rts
.endproc


.rodata
HEX_CHARS_UPPER:    .byte "0123456789ABCDEF"
HEX_CHARS_LOWER:    .byte "0123456789abcdef"