X86-64 Multiply Instruction

Question 1

Multiplying any 2 numbers represented with w bits, we must store result in ______ bits to avoid overflow

Answer 1

2w

Question 2

There are two different instructions to accomplish multiplication. ____ for signed interpretations and_____ for unsigned interpretations

Answer 2

ImulX, mulX

Question 3

ImulX src

Answer 3

Result in 2w bits relative to suffix

Question 4

ImulX

Answer 4

Result in w bits equivalent to suffix

Question 5

ImulX Imm, Src, Destiny

Answer 5

Result in w bits equvivalent to suffix

Question 6

ALU uses _____ 8-byte registers to accomplish 16-byte result

Answer 6

Two

Question 7

This only works with ____/____ register pair. No other register pairs can be used

Answer 7

%rdx, %rax

Question 8

Code for 128 bit unsigned multiply
# dest in %rdi, x in %rsi, y in %rdx

Answer 8

Movq %rsi, %rax
Mule %rdx
Movq %rax, (%rdi) -> YOU CAN ALSO MOVE VALUE TO ADRESS IN MEMORY
Movq %rdx, 8(%rdi)

Question 9

If we have two-byte values that we multiple together using mule %cx giving us a 4 byte results were the least significant 2 bytes are in %ax and the most significant 2 bytes are in do then
1. ___ can be in the upper 6 bytes in both %rax and %rdx register
2. We must _____ the 2 byte values in %ax and %dx also we have a 4 byte value we can use!

Answer 9

Garbage, combine

Question 10

%ax: 0x1234, assume %eax = 0x784f1234
%dx0056 assume %edx = 0xab330056
Want 4 byte rental 0x00561234

Answer 10

Shll $16, %edx. %edxL 0x00560000
Movzwl %ax, %eax. %eax: 0x00001234
Orl %edx, %eax. —> 0x00561234