Question

Understanding Assembly Language. For each problem, show the contents or setting of the requested items after executing the instructions.

mov eax, 0FFFFFBFDh ; i.e., -1027

mov ebx, -16        ; i.e., FFFFFFF0h

mov edx, 0

idiv bl

Show the hexadecimal digits in eax:_______________

Show the hexadecimal digits in edx:_______________

mov eax, 0FFFFFBFDh ; i.e., -1027

mov ebx, -16        ; i.e., FFFFFFF0h

mov edx, 0

cwd

idiv bx

Show the hexadecimal digits in eax:_______________

Show the hexadecimal digits in edx:_______________

mov eax, 0FFFFFBFDh ; i.e., -1027

mov ebx, -16        ; i.e., FFFFFFF0h

mov edx, 0

cdq

idiv ebx

Show the hexadecimal digits in eax:_______________

Show the hexadecimal digits in edx:_______________

Answer 1

mov eax, 0FFFFFBFDh ; i.e., -1027 => eax = 0xFFFFFBFD => ax = 0xFBFD

mov ebx, -16; i.e., FFFFFFF0h => ebx = 0xFFFFFFF0 => bl = 0xF0

mov edx, 0 => edx = 0x00000000

idiv bl =>

=> al = ax/bl = 0xFBFD / 0xF0 = 0x40

=> ah = ax%bl = 0xFBFD % 0xF0 = 0x03

Show the hexadecimal digits in eax: 0xFFFF0340

Show the hexadecimal digits in edx: 0x00000000

mov eax, 0FFFFFBFDh ; i.e., -1027 => eax = 0xFFFFFBFD => ax = 0xFBFD

mov ebx, -16 ; i.e., FFFFFFF0h => ebx = 0xFFFFFFF0 => bx = 0xFFF0

mov edx, 0   => edx = 0x00000000

cwd => Sign Extend AX into DX => dx:ax = 0xFFFFFBFD

idiv bx =>

=> ax = dx:ax/bx = 0xFFFFFBFD / 0xFFF0 = 0x0040‬

=> dx = dx:ax%bx = 0xFFFFFBFD % 0xFFF0 = 0x0003

Show the hexadecimal digits in eax: 0xFFFF0040

Show the hexadecimal digits in edx: 0x00000003

mov eax, 0FFFFFBFDh ; i.e., -1027 => eax = 0xFFFFFBFD

mov ebx, -16; i.e., FFFFFFF0h  => ebx = 0xFFFFFFF0

mov edx, 0   => edx = 0x00000000

cdq => Sign Extend eax into edx => edx:eax = 0x00000000FFFFFBFD

idiv ebx =>

=> eax = edx:eax/ebx = 0x00000000FFFFFBFD / 0xFFFFFFF0 = 0x00000040‬

=> edx = edx:eax%ebx = 0x00000000FFFFFBFD % 0xFFFFFFF0 = 0x00000003

Show the hexadecimal digits in eax:  0x00000040‬

Show the hexadecimal digits in edx: 0x00000003