reverser.asm

将输入的字母的大小写变换。小写得变大写。

;----------------------------------------------------------------------------
; CPSC 355 Example Program
; "Reverser"
; Author:  xuan wang
; Date:    April 29, 2001
;----------------------------------------------------------------------------

[GLOBAL mystart]                  ; export the start address

;----------------------------------------------------------------------------
[SECTION .text]
;----------------------------------------------------------------------------

; code belongs in this section starting here

mystart:
         mov  ah, 09h             ; select write string function
         mov  edx, prompt         ; put address of string in EDX
         int  0f1h                ; call OS interrupt 0F1H

         mov  byte [buffer], 98   ; buffer can hold 98 characters
         mov  byte [buffer+1], 0  ; reuse 0 characters from last input
         mov  ah, 0ah             ; select buffered input function
         mov  edx, buffer         ; put buffer address in EDX
         int  0f1h                ; call OS interrupt 0F1H

         mov  ah, 02h             ; select write character function
         mov  dl, 10              ; output a newline
         int  0f1h

         movzx ecx, byte [buffer+1];load ECX with number of characters read
         mov  esi, buffer+1       ; load adress of input text into ESI
         add  esi, ecx            ; move to end of text
         std                      ; set direction flag to go backwards
         mov  ah, 02h             ; select write character function
top:
         lodsb                    ; grab a character into AL
         mov  dl, al              ; put it into DL for function
         int  0f1h                ; call OS interrupt 0F1H
         loop top                 ; continue while ECX > 0

         mov  ah, 02h             ; select write character function
         mov  dl, 13              ; output a carriage return
         int  0f1h
         mov  ah, 02h             ; select write character function
         mov  dl, 10              ; output a newline
         int  0f1h

         ret


;----------------------------------------------------------------------------
[SECTION .data]
;----------------------------------------------------------------------------

; all initialized data variables and constant definitions go here

prompt   db   "Enter a string:", 13, 10, "> $"


;----------------------------------------------------------------------------
[SECTION .bss]
;----------------------------------------------------------------------------

; all uninitialized data elements go here

buffer   resb 100                 ; buffer to store input characters