Assembly big numbers calculator

问题

I've been given an assingment to make a calculator in 8086 assembly that will add, substract, multiply and divide big decimal numbers. These numbers can be 30 digits long at most. I've used 3 arrays to house these numbers (num1, num2, result). I'm stuck at the addition, because every time I run the program, it displays that the result array is empty (it shows a plus sign and 60 zeroes) can you tell what is wrong with my code?

ADDER:

    MOV     BP, offset num1
    MOV     SI, offset num2
    MOV     DI, offset result
    MOV     CL, byte ptr CS:[BP]
    MOV     CH, byte ptr CS:[SI]
    CMP     CL, CH
    JZ  addgood
    CMP     CL, '-'
    JNZ svers

   MOV     byte ptr CS:[BP], '+'                                       
   MOV     SI, offset num1
   MOV     BP, offset num2
   JMP SUBSTRACTOR
svers:

   CMP     CH, '-'
   MOV     byte ptr CS:[SI], '+'
   JMP SUBSTRACTOR

addgood:

lastdigit1:

    MOV     AL, byte ptr CS:[BP]
    CMP     AL, 127
    JZ      gotlastdigit1
    INC     BP
JMP lastdigit1
gotlastdigit1:

lastdigit2:
   MOV     AL, byte ptr CS:[SI]
   CMP     AL, 127
   JZ      gotlastdigit2
   INC     SI
   JMP lastdigit2

gotlastdigit2:

   MOV DI, offset result
   ADD DI, 60

initialaddition:

   CMP byte ptr CS:[BP], '+'
   JNZ notover1 
   JMP num1end
 notover1:
   CMP byte ptr CS:[BP], '-'
   JNZ notover2 
   JMP num1end
notover2:
   CMP byte ptr CS:[SI], '+'
   JNZ notover3 
   JMP num2end
notover3:
   CMP byte ptr CS:[SI], '-'
   JNZ notover4
   JMP num2end
notover4:
   MOV CH, byte ptr CS:[BP]
   MOV CS:[DI], CH
   MOV CH, byte ptr CS:[SI]    
   ADD CS:[DI], CH
   DEC BP
   DEC SI
   DEC DI
JMP initialaddition
afteriniadd:
   DEC DI
   MOV CL, 127
   MOV CS:[DI], CL
   MOV DI, offset result
   ADD DI, 60

truaddition:
   MOV CH, 0
   MOV CL, byte ptr CS:[DI]
   CMP CL, 10
   JNAE movealong
   CALL pisdod
movealong:    
   MOV CS:[DI], CL
   DEC DI
   MOV CL, byte ptr CS:[DI]
   CMP CL, 127
   JZ  isspecial    
   ADD CS:[DI], CH

 JMP truaddition
 isspecial:
   CMP CH, 0

   JZ  afteradd

   MOV CS:[DI], CH


afteradd:

   DEC DI
   MOV CS:[DI], 127
   MOV SI, offset num1
   MOV CL, CS:[SI]
   MOV DI, offset result
   CMP CL, '+'
   JZ  adplus
   MOV byte ptr CS:[DI], '-'
   JMP adminus
adplus:

   MOV byte ptr CS:[DI], '+'

adminus:

RET

The sub-procedures

num1end:
    MOV CL, '-'
    CMP byte ptr CS:[SI], CL
    JNZ noneed1 
    JMP afteriniadd
noneed1:
    MOV CL, '+'
    CMP byte ptr CS:[SI], CL
    JNZ noneed2
    JMP afteriniadd
noneed2:
    MOV CL, byte ptr CS:[SI]
    MOV byte ptr CS:[DI], CL
    DEC DI
    DEC SI
JMP num1end    

;......................................

num2end:
    MOV CL, '-'
    CMP byte ptr CS:[BP], CL
    JNZ noneed3
    JMP afteriniadd
noneed3:
    MOV CL, "+"
    CMP byte ptr CS:[BP], CL
    JNZ noneed4
    JMP afteriniadd
noneed4:
    MOV CL, byte ptr CS:[BP]
    MOV byte ptr CS:[DI], CL
    DEC DI
    DEC BP
JMP num2end

pisdod:
    CMP CL, 10
    JGE notyet 
    RET
notyet:
    SUB CL, 10
    INC CH
JMP pisdod

And array declarations

num1    db  31 DUP(?), 127
num2    db  31 DUP(?), 127
result  db  61 DUP(?), 127

With 127 serving as a marker where do the digits begin and end.

回答1:

I figured it out myself, finally. Turns out I didn't need to use the DEC DI in afteradd: part. That command caused the marker to be placed twice, one after another, which fooled the procedure that was supposed to print the result.

来源：https://stackoverflow.com/questions/23298622/assembly-big-numbers-calculator