Assembly Assignment

Problem:
Write a subprogram which will take input from the main program as-
A-8 bit number(save in AL)
B-32 bit number(save in BX:CX)
C-16 bit number(save in DX)
D-8 bit number(save in AH)


Solution:

.stack 100h

.data
A db 151
B dd 1048576
C dw 3298
D db 78

.code
main proc
  mov al, A
  mov ah, D
  mov dx, C
  lea si, B ;B is a double word, so to store B we have to treat it like an array
  mov bx, [si]
  mov cx, [si + 2] ;+2 because double word, advance 2 bytes

  call custom_function
  ret
main endp

custom_function proc
   ;Inputs A, B, C, D in Al, (BX(High) + CX, (Low)), DX and AH respectively
   ;Storing the input in the stack so that data is not lost
   push ax
   push bx
   push cx
   push dx

   ;Do, something here

   ;Restore the data in the registers
   pop dx
   pop cx
   pop bx
   pop ax

   ret
custom_function endp