Write a procedure named BitwiseMultiply that multiplies any unsigned 32-bit inte

Question

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. We will assume that the product is never larger than 32 bits. One possible approach is to use a loop to shift the multiplier to the right, keeping track of the number of shifts that occur before the Carry ?ag is set. The resulting shift count can then be applied to the SHL instruction, using the multiplicand as the destination operand. Then, the same process must be repeated until you ?nd the last 1 bit in the multiplier.

Prompt the user to enter the multiplicand, the multiplier and display the result after the procedure returns the result to the main procedure.

WRITE THE CODE IN ASSEMBLY LANGUAGE AND ALSO WRITE THE COMMENTS ON EACH LINE SO I CAN UNDERSTAND PROPERLY AND SCREENSHOT THE OUTPUT.

Explanation / Answer

Description: Write a procedure named FastMultiply 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. (We will assume that the product is never larger than 32 bits.) Last update: 11/20/02 (uses new ReadDec procedure) ! 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 jmp L1 .ELSE mov ebx,eax .ENDIF cmp eax,0 je quit L2: mWrite "Enter an unsigned integer: " call ReadDec .IF CARRY? mWrite jmp L2 .ENDIF mWrite ; 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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