Assembly Language MASM32 Can someone help me by telling me what I\'m doing wrong

Question

Assembly Language MASM32

Can someone help me by telling me what I'm doing wrong with this code, it complies but doesn't give me the right answer. It's in MASM 32bit using Irvine32; assembly language. The question instructions for this problem is located right under this sentence.

TITLE:

; Write a procedure named BitWiseMultiply that multiplies any unsigned 32-bit

;integer by EAX, using only shifting and addition. Pass the integer to the procedure in the EBX ;register, and return the product in the EAX register. Write a short test program that calls the ;procedure and displays the product.

INCLUDE Irvine32.inc

.data

str1 BYTE "Results", 0dh,0ah,0dh,0ah,0

Multi DWORD 200

MultiBy DWORD 5

Result DWORD 32 DUP (?)

ResultSize DWORD ?

.code

main PROC

        call Clrscr

        mov ebx, Multi

       mov eax, MultiBy

        call BitwiseMultiply

       call Display

       exit

       main ENDP

BitwiseMultiply PROC uses ecx edx esi

mov ecx, 32

mov edx, eax

mov esi, 0

L1:

   clc

L2:

   inc esi

   add eax, Result[esi]

   Loop L3

   ret

L3:

   jc L4

   shl edx,1

   jmp L2

L4:

   mov Result[esi], ebx

   inc esi

   loop L1

   mov ResultSize, esi

   mov eax, Result[esi]

   mov ecx, ResultSize-1

BitwiseMultiply ENDP

Display PROC

mov edx, OFFSET str1

call WriteString

call WriteDec

call Crlf

call Crlf

ret

Display ENDP

END main

Explanation / Answer

INCLUDE Irvine32.inc
INCLUDE Macros.inc

.data
str1 BYTE "Fast Multiplication Program - ** DEMO **",
           0dh,0ah,0dh,0ah,0

.code
main PROC
   call Clrscr
   mov edx,OFFSET str1
   call WriteString

L1:
   mWrite "Enter an unsigned integer (0 to quit): "
   call ReadDec
   .IF CARRY?
      mWrite <"Error: Integer is out of range",0dh,0ah>
      jmp L1
   .ELSE
   mov ebx,eax
   .ENDIF
   cmp eax,0
   je quit

L2:
   mWrite "Enter an unsigned integer: "
   call ReadDec
   .IF CARRY?
      mWrite <"Error: Integer is out of range",0dh,0ah>
      jmp L2
   .ENDIF

   mWrite <"--------------------------------",0dh,0ah>

   ; EBX = multiplicand, EAX = multiplier
   call FastMultiply   ; EAX = product
   jc   L1   ; CF=1 indicates error

   mWrite "The product is:       "
   call WriteDec   ; display product
   call Crlf
   call Crlf
   jmp L1

quit:
   exit
main ENDP

;-----------------------------------------------------------------
FastMultiply PROC uses ecx edx esi

COMMENT !
Multiplies any unsigned 32-bit integer by EAX, using only
shifting and addition.
Receives: EBX = multiplier, EAX = multiplicand
Returns: If CF=0, EAX = product; otherwise, CF=1 and
          EAX equals 0.

The algorithm used here is more elegant than the one discussed
on page 237.

    FOR count = 1 to 32
       if lowbit(multiplier) == 1
         product += multiplicand;       ; check Carry flag
       multiplier SHR 1;
       multiplicand SHL 1;       ; check Carry flag
    NEXT count

This was obtained from the web site of Dr. Wang Jian-Sheng at
the National University of Singapore (http://www.cz3.nus.edu.sg/~wangjs/)
----------------------------------------------------------------!

   mov edx,0   ; clear product to zero
   mov ecx,32   ; loop counter

L1:   test ebx,1   ; LSB set?
   jz   L2   ; no: skip next statement
   add edx,eax   ; yes: add multiplicand to product
   jc   L3   ; display error if CF=1

L2:
   shr ebx,1   ; shift multiplier right
   shl eax,1   ; shift multiplicand left
   jc   L3   ; display error if CF=1
   loop L1   ; repeat for 32 bits

L3:   mov eax,edx   ; return the product

   ret
FastMultiply ENDP

END main

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