PRESERVE8
    AREA MyCode, CODE, READONLY
    EXPORT calc

calc
    import my_fprint
    import my_print ;debug
    import my_getchar
    import my_putchar
    MOV r3,#0xA     ;constant
    LDR r0,=cal
    BL  my_fprint

get_new
    MOV r0,#0x0A
    BL  my_putchar  ;outputs line feed between new things
    MOV r4,#0       ;reinitilise the saved number register
    BL my_getchar
;next_dig
    PUSH{r0}
    BL my_putchar
    POP{r1}
;num handling
    CMP r1,#0x39        ;ie temp r0-0x39
    BGT equals          ;assume '=' only other larger value
    CMP r1,#0x30        ;ie temp r0 -0x30
    BLT op              ;assume operators only smaller values
AsciiToInt
    MOV r2,#0           ;store result here

;Argument needs to be compiled of get chars
LDR r4,=argument    ;load start address for argument

;LAB SLIDES
NextAscii
    LDRB r3,[r4],#1 ;
    CMP r3,#0x0D
    BEQ get_new
    AND r3,#0x30        ;separate the decimal digit from ASCII character
    ADD r2,r3,r2
    LSL r5,r2,#3        ;multiply by 8, r5 = r2*8
    ADD r2,r5,r2, LSL #1    ;here we have r2 = r5 + r2*2
    B   NextAscii
done
;OLD CODE

;   B   asc2int
;   ;SUB r1,r1,#0x30        ;convert to int
;   MLA r4,r4,r3,r1     ;r4 = r4*10 + r0
;   PUSH {r4}
;   BL  my_getchar
;   MOV r1,r0
;   CMP r1,#0x0D        ;checks if multiple digit number
;   BNE next_dig        ;no CR at end therefore must be a digit
;   BL  my_putchar      ;beginning of line
;   B   get_new         ;end of number


/*OPERATIONS*/
op
    CMP r1,#"+"
    BEQ plus

    CMP r1,#"-"
    BEQ minus

    CMP r1,#"/"
    BEQ div

    CMP r1,#"*"
    BEQ mult

plus
    BL my_getchar
    CMP r0,#0x0D    ;verifies that the next charachter is an enter
    BNE error   ;if not then the format is incorrect
    BL  my_putchar  ;beginning of line
    POP {r5}
    POP {r6}
    ADD r5,r6,r5    ;add arguments
    PUSH {r5}
    B   get_new ;return from subroutine

minus
    BL my_getchar
    CMP r0,#0x0D    ;verifies that the next charachter is an enter
    BNE error   ;if not then the format is incorrect
    BL  my_putchar  ;beginning of line
    POP {r5}
    POP {r6}
    SUB r5,r6,r5    ;add arguments ;old number - new number
    PUSH {r5}
    B   get_new ;return from subroutine

div
    BL my_getchar
    CMP r0,#0x0D    ;verifies that the next charachter is an enter
    BNE error   ;if not then the format is incorrect
    BL  my_putchar  ;beginning of line
    POP {r5}
    POP {r6}
    CMP r5,#0
    BEQ error       ;divide by 0 error
    UDIV r5,r6,r5   ;divide arguments   ;old number/new number; r6/r5
    PUSH {r5}
    B   get_new ;return from subroutine

mult
    BL my_getchar
    CMP r0,#0x0D    ;verifies that the next charachter is an enter
    BNE error   ;if not then the format is incorrect
    BL  my_putchar  ;beginning of line
    POP {r5}
    POP {r6}
    MUL r5,r6,r5    ;multiply arguments
    PUSH {r5}
    B   get_new ;return from subroutine

equals
    BL  my_getchar
    CMP r0,#0x0D    ;verifies that the next charachter is an enter
    BNE error   ;if not then the format is incorrect
    BL  my_putchar
    MOV r0,#0x0A    ;LF
    BL  my_putchar  ;outputs line feed between new things
    POP {r1}
    MOV r2,#0   ;counter

dec2asc
    ADD r2,r2,#1    ;increment counter
    CMP r1,r3   ;temp r1 - 10
    BLT output  ;if no more digits jump
    UDIV r4,r1,r3   ;r4 = r1/10
    MLS  r5,r4,r3,r1 ;r5 = r1- r4*10
    ;r5 = r1%10 and r4 = r1/10
    PUSH {r5}   ;push LSB onto stack
    MOV r1,r4   ;continue with remaining digits
    B   dec2asc

output
    SUB r2,r2,#1 ;decrement counter
    ADD  r0,r1,#0x30 ;MSB integer to ascii
    BL  my_putchar  ;outputs an integer
    POP {r1}
    CMP r2,#0
    BGT output
    B   stop

error
    LDR r0,=err
    BL  my_fprint
    B stop


/*END OPERATIONS*/

stop B stop

    ALIGN       ;aligns code (but also data) to a memory boundary
    AREA MyData, DATA, READWRITE

;strings
err DCB 10,13,"An error occured in processing",0,10,13  ;NULL;LF;CR decimal
cal DCB 10,10,13,"NEW CALCULATOR",0,13  ;NULL;LF;CR decimal
y   DCB "point",0;for debug
;zero DCB "cannot divide by zero",0
;inv DCB "invalid input formatting",0

    END             ;designates end of source line