Division of Unsigned Numbers in x86
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Division of Unsigned Numbers in x86

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Questions and Answers

What will be stored in the DX register after performing a division of unsigned numbers with the numerator in AX and the denominator in CL?

  • The carry flag
  • The remainder (correct)
  • The least significant bit
  • The quotient

    • In a doubleword/word division, where is the most significant word of the numerator stored?

  • In DX (correct)
  • In AH
  • In AX
  • In AL

    • What occurs if an overflow happens during signed arithmetic operations using the AL register?

  • The result is capped at 255.
  • Both overflow and carry flags are set.
  • AL automatically resets to zero.
  • The result appears as a negative value incorrectly. (correct)

    • What value allows the AL register to handle unsigned values during arithmetic operations?

    <p>255</p> Signup and view all the answers

    Which instruction logically shifts the operand to the right and fills the most significant bit with 0?

    <p>SHR</p> Signup and view all the answers

    What is the outcome of a logical shift left operation on a binary number?

    <p>All bits shift left with the LSB filled with 0</p> Signup and view all the answers

    What maximum quotient can be obtained when performing a division with a byte dividend?

    <p>FFH</p> Signup and view all the answers

    When performing unsigned multiplication, what register will contain the lower half of the result when multiplying two words?

    <p>AX</p> Signup and view all the answers

    What condition leads to a Divide Error message during unsigned division?

    <p>The denominator is set to zero.</p> Signup and view all the answers

    In unsigned multiplication of a byte by a byte, where must one operand be located?

    <p>In the AL register.</p> Signup and view all the answers

    What is the result location for the operation of word times word multiplication?

    <p>Both AX and DX.</p> Signup and view all the answers

    What must be true of the AH register before performing a word-by-byte multiplication?

    <p>It must be set to zero.</p> Signup and view all the answers

    What will be the result locations after performing a byte over byte division?

    <p>AL holds the quotient, AH holds the remainder.</p> Signup and view all the answers

    What happens if the quotient from an unsigned division operation is too large for the assigned register?

    <p>An interrupt is triggered, yielding a Divide Error.</p> Signup and view all the answers

    What values do AX and DX contain after performing a word times word multiplication?

    <p>AX contains the lower word, DX contains the higher word.</p> Signup and view all the answers

    What registers are essential for performing unsigned arithmetic operations in x86 architecture?

    <p>AX, AL, AH, DX.</p> Signup and view all the answers

    What happens to the carry flag (CF) after a subtraction operation?

    <p>It holds borrows instead of carries.</p> Signup and view all the answers

    What is the result of the operation 'SUB CH, 44H' when CH starts at 22H?

    <p>The result is 0DEH.</p> Signup and view all the answers

    When executing an addition loop in assembly as shown, when should the loop terminate?

    <p>When the value in CX becomes zero.</p> Signup and view all the answers

    Which operation effectively subtracts a memory location's content from a register in assembly language?

    <p>SUB</p> Signup and view all the answers

    What is a consequence of the instruction 'ADC BX, 0' in the loop shown?

    <p>It adds the carry flag to BX.</p> Signup and view all the answers

    What is a necessary step for initializing the Data Segment (DS) in the code segment shown?

    <p>Move DS with the value of AX.</p> Signup and view all the answers

    During multiword addition, what is the purpose of the instruction 'INC SI'?

    <p>To point to the next data word.</p> Signup and view all the answers

    What does the 'MOV AH, 4CH' instruction signify in the ending part of the code?

    <p>It sets up an interrupt to terminate the program.</p> Signup and view all the answers

    Study Notes

    Division of Unsigned Numbers

    • Division operations involving unsigned numbers in x86 processors utilize registers AX, AL, AH, and DX.
    • Four distinct division cases exist: byte/byte, word/word, word/byte, doubleword/word.
    • When dividing by zero or when the quotient exceeds the capacity of the assigned register, a "Divide Error" exception occurs, halting the program.

    Division Cases

    • Word/Word:
      • Numerator is in AX and DX (most significant word in DX, least significant in AX).
      • Denominator can be in a register or memory location.
      • After division, the quotient is stored in AX, and the remainder in DX.
      • The maximum attainable quotient is FFFFH.
    • Byte/Byte:
      • Numerator is in AL, and AH must be cleared (set to zero).
      • Denominator cannot be immediate but can be in a register or memory.
      • After division, the quotient is stored in AL, and the remainder in AH.

    Multiplication of Unsigned Numbers

    • Multiplication operations in x86 processors utilize registers AX, AL, AH, and DX.
    • Three multiplication cases are possible: byte × byte, word × word, and byte × word.

    Multiplication Cases

    • Byte × Byte:
      • One operand must be in the AL register, and the second operand can be in a register or memory location.
      • The result is stored in AX after the multiplication.
    • Word × Word:
      • One operand must be in AX, and the second operand can be in a register or memory location.
      • The result is a 32-bit value: AX holds the lower word, and DX holds the higher word.
    • Byte × Word:
      • Similar to word × word but with the byte operand in AL and AH set to zero.

    Signed Number Arithmetic Operations: Overflow Problem

    • Signed number arithmetic can lead to overflow if the result goes beyond the capacity of the register.
    • An 8-bit overflow occurs when the signed result is greater than 127 or less than -128.
    • Despite overflow, the result is a correct 8-bit signed number.

    Logic Instructions: Shift Right (SHR)

    • Logical shift right shifts the operand right bit by bit, filling the MSB with 0.
    • The LSB is moved to the carry flag (CF) during each shift.

    Logic Instructions: Shift Left (SHL)

    • Logical shift left is the opposite of SHR, shifting the operand left.
    • The LSB is filled with 0, and the MSB is moved to CF, similar to SHR.

    Subtraction

    • The SUB instruction subtracts the second operand from the first operand and stores the difference in the first operand.
    • Examples:
      • SUB CL,BL CL = CL – BL
      • SUB AX,SP AX = AX – SP
      • SUB DI,TEMP[SI] DI = DI - TEMP[SI]

    Flags After Subtraction

    • The carry flag (C) and the auxiliary carry flag (A) hold borrow values instead of carries after subtraction.
    • This reflects the potential for borrowing during a subtraction operation.

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    Description

    This quiz covers the division operations involving unsigned numbers in x86 processors, detailing four distinct cases. It explains how registers are utilized during these operations and addresses potential exceptions like 'Divide Error'. Test your knowledge on how division works in the x86 architecture!

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