5. Program to BetterRandomRange Procedure in Assembly Language using Visual Studio

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Chapter 5

Procedures

Assembly Language Programming Exercise

Problem # 5:

The RandomRange procedure from the Irvine32 library generates a  pseudorandom integer between 0 and N 1. Your task is to create an improved version that generates an integer between M and N 1. Let the caller pass M in EBX and N in EAX. If we call the procedure BetterRandomRange, the following code is a sample test:
     mov  ebx,-300 ; lower bound
     mov  eax,100 ; upper bound
     call BetterRandomRange
Write a short test program that calls BetterRandomRange from a loop that repeats 50 times. Display each randomly generated value.

Solution:

INCLUDE Irvine32.inc

.data

.code
    main PROC
        call Clrscr
        mov eax, -300
        mov ebx, 100
        mov ecx, 50

        L1:
            push eax            ; doesn't change range
            push ebx

            call BetterRandomRange

            pop ebx
            pop eax
        Loop L1

        call WaitMsg
        exit
    main ENDP

    BetterRandomRange PROC
        sub ebx, eax        ;mov 400 to ebx
        xchg ebx, eax        ;random works with eax
        call RandomRange    ; generate random int
        neg ebx              
        sub eax, ebx        ;sub 300 from eax to define range
        call WriteInt        ; write signed decimal
        call Crlf
        ret
    BetterRandomRange ENDP

END main