## X86 Instructions and ARM Architecture

Read this article, which gives two examples of instructions set architectures (ISAs). Look over how the different microprocessors address memory. Take note of similarities and differences of format, instructions and type of instructions, and addressing modes between these two as well as between these and the MIPS instructions of the previous sections.

### Logic Instructions

#### The instructions on this page deal with bit-wise logical instructions.

All logical instructions presented in this section are executed in the, as the name already suggests, the *arithmetic logic unit*.

#### binary operations

These instructions require *two* operands.

##### logical `and`

and mask, destination |
GAS Syntax |

and destination, mask |
Intel Syntax |

**operation**

`and`

performs a bit-wise `and`

of the two operands, and stores the result in `destination`.

**example**

movl$0x1,%edx; edx ≔ 1 movl$0x0,%ecx; ecx ≔ 0 andl%edx,%ecx; ecx ≔ edx ∧ ecx ; here ecx would be 0 because 1 ∧ 0 ⇔ 0

**application**

- An
`and`

can be used to calculate the*intersection*of two “sets”, or a value representing a “mask”. Some programming language require that Boolean values are stored*exactly*as either`1`

or`0`

. An`and rax, 1`

will ensure only the LSB is set, or not set. - If partial register addressing is not available in the desired size, an
`and`

can be used for a destination mod mask operation, that is the remainder of integer division. For that,`mask`has to contain the value 2^{n}-1 (i. e. all lower bits set until a certain threshold), where 2^{n}equals your desired divisor.

##### logical `or`

or addend, destination |
GAS Syntax |

or destination, addend |
Intel Syntax |

**operation**

The `or`

instruction performs a bit-wise `or`

of the two operands, and stores the result in `destination`.

**example**

movl$0x1,%edx; edx ≔ 1 movl$0x0,%ecx; ecx ≔ 0 orl%edx,%ecx; ecx ≔ edx ∨ ecx ; here ecx would be 1 because 1 ∨ 0 ⇔ 1

**application**

- An
`or`

can be used to calculate the*union*of two “sets”, or a value representing a “mask”.

##### logical `xor`

xor flip, destination |
GAS Syntax |

xor destination, flip |
Intel Syntax |

**operation**

Performs a bit-wise `xor`

of the two operands, and stores the result in `destination`.

**example**

movl$0x1,%edx; edx ≔ 1 movl$0x0,%ecx; ecx ≔ 0 xorl%edx,%ecx; ecx ≔ edx ⊕ ecx ; here ecx would be 1 because 1 ⊕ 0 ⇔ 1

**application**

`xor rax, rax`

(or any GPR twice) will clear all bits. It is a specially recognized word. However, since`xor`

affects flags it might introduce bogus dependencies.

##### common remarks

**side effects for and, or, and xor**

`OF`≔ 0`CF`≔ 0`SF`becomes the value of the most significant bit of the calculated`result``ZF`≔`result`= 0`PF`is set according to the result

#### unary operations

##### logical `not`

**not** argument

**operation**

Performs a bit-wise inversion of `argument`.

**side-effects**

None.

**example**

movl$0x1,%edx; edx ≔ 1 notl%edx; edx ≔ ¬edx ; here edx would be 0xFFFFFFFE because a bitwise NOT 0x00000001 = 0xFFFFFFFE

**application**

`not`

is frequently used to get a register with all bits set.