Question

Assembly Language For x86 Processors 7th edition

When you write programs to solve the programming exercises, use multiple procedures when possible. Follow the style and naming conventions used in this book. Use explanatory comments in your programs at the beginning of each procedure and next to nontrivial statements.

Random Strings

Create a procedure that generates a random string of length L, containing all capital letters. When calling the procedure, pass the value of L in EAX, and pass a pointer to an array of byte that will hold the random string. Write a test program that calls your procedure 20 times and displays the strings in the console window.

Answer 1

;Random Strings.

INCLUDE Irvine32.inc
TAB = 9                       ;ASCII code for Tab
strLen=10                     ;length of the string

.386
.model flat,stdcall
.stack 4096
ExitProcess PROTO, dwExitCode:DWORD

.data
str1 BYTE"The 20 random strings are:", 0
arr1 BYTE strLen DUP(?)

.code
main PROC
     mov ed x, OFFSET str1         ;"The c20 random strings are:"
     call WriteString              ;Writes string
     call Crlf                     ;Writes an end-of-line sequence to the console window.
     mov ecx,20                    ;Create 20 strings

 L1: mov esi,OFFSET arr1           ;ESI: array address
     mov eax,strLen                ;EAX: string length
     call RandomString             ;generates the random string
     call Display
     mov al,TAB
     call WriteChar                ;leaves a tab space
     exit
main ENDP

     RandomString PROC USES eax esi
     mov ecx,eax                   ;ECX = string length

L1:  mov eax, 26
     call RandomRange
     add eax,65                    ;EAX gets ASCII value of a capital letter
     mov arr1[esi],eax
     inc esi

     loop L1

     RandomString EXDP

     Display PROC USES eax esi     ;Displays the generated random string

     mov ecx,eax                   ;ECX=string length

L1:  mov eax, arr1[esi]            ;EAX = ASCII value
     call WriteChar                ;writes the letter

     inc esi

     loop L1

     Display ENDP


        call dumpregs

        INVOKE ExitProcess,0

END main