Jason Aller Floppy Collection/181.img/TASM-101.ZIP/REVERSE.ASM

Assembly Source File | 1988-10-31 | 2KB | 41 lines

   DOSSEG
   .MODEL SMALL
   .STACK 100h
   .DATA
MAXIMUM_STRING_LENGTH  EQU  1000
StringToReverse  DB  MAXIMUM_STRING_LENGTH DUP(?)
ReverseString    DB  MAXIMUM_STRING_LENGTH DUP(?)
   .CODE
   mov  ax,@data
   mov  ds,ax                       ;set DS to point to the data segment
   mov  ah,3fh                      ;DOS read from handle function #
   mov  bx,0                        ;standard input handle
   mov  cx,MAXIMUM_STRING_LENGTH    ;read up to maximum number of characters
   mov  dx,OFFSET StringToReverse   ;store the string here
   int  21h                         ;get the string
   and  ax,ax                       ;were any characters read?
   jz   Done                        ;no, so you're done
   mov  cx,ax                       ;put string length in CX, where
                                    ; you can use it as a counter
   push cx                          ;save the string length
   mov  bx,OFFSET StringToReverse
   mov  si,OFFSET ReverseString
   add  si,cx
   dec  si                          ;point to the end of the
                                    ; reverse string buffer
ReverseLoop:
   mov  al,[bx]                     ;get the next character
   mov  [si],al                     ;store the characters in reverse order
   inc  bx                          ;point to next character
   dec  si                          ;point to previous location in reverse buffer
   loop ReverseLoop                 ;move next character, if any
   pop  cx                          ;get back the string length
   mov  ah,40h                      ;DOS write from handle function #
   mov  bx,1                        ;standard output handle
   mov  dx,OFFSET ReverseString     ;print this string
   int  21h                         ;print the reversed string
Done:
   mov  ah,4ch                      ;DOS terminate program function #
   int  21h                         ;terminate the program
   END