SHIFT OPERATIONS

I already knew this in C, which is called bitwise operators. It’s a fast way to multiply or divide by powers of 2. For example, shifting a number to the left by 1 is equivalent to multiplying it by 2. Similarly, shifting a number to the right by 1 is equivalent to dividing it by 2.

Operator	Description	Result
shr	Logical Right Shift	Shifts the bits to the right
shl	Logical Left Shift	Shifts the bits to the left
sar	Arithmetic Right Shift	Shifts the bits to the right, preserving the sign bit
sal	Arithmetic Left Shift	Shifts the bits to the left; an alias for shl, same opcode

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SHR Operation

The shr instruction is used to perform logical right shift operations. It shifts the bits of the operand to the right by a specified number of bits.

section .text
    .global _start
_start:
        mov eax, 2 ; 0010 = 2
        shr eax, 1  ; shift the bits to the right one spot -> 0001 = 1
                    ; this equivalent to dividing by 2 but it's faster

---

SHL Operation

The shl instruction is used to perform logical left-shift operations. It shifts the bits of the operand to the left by a specified number of bits.

section .text
    .global _start

_start:
        mov eax, 2 ; 0010 = 2
        shl eax, 1  ; shift the bits to the left one spot -> 0100 = 4
                    ; this equivalent to multiplying by 2 but it's faster

---

SAR Operation

The sar instruction is used to perform arithmetic right shift operations. It shifts the bits of the operand to the right by a specified number of bits, while preserving the sign bit.

section .text
    .global _start

_start:
        mov eax, -2 ; 1110 = -2
        sar eax, 1  ; shift the bits to the right one spot -> 1111 = -1
                    ; this equivalent to dividing by 2 but it's faster

---

SAL Operation

The sal instruction performs an arithmetic left shift. It is an alias for shl: both assemble to the same opcode, because shifting left has no sign bit to preserve. Only the right shifts differ, where sar keeps the sign and shr does not.

section .text
    .global _start

_start:
        mov eax, -2 ; 1110 = -2
        sal eax, 1  ; shift the bits to the left one spot -> 1100 = -4
                    ; this equivalent to multiplying by 2 but it's faster