SHR

Table of Contents

1. SHR（shr）
   1. Basic purpose
   2. Instruction execution process
   3. Instruction format
   4. Behavioral characteristics
   5. Common uses

SHR（shr）

Basic purpose

SHR (logical right shift) shifts the operand right by n bits, filling the left side with 0s.
Mathematically: dest = floor(dest / 2^n)。

Instruction execution process

• Shift right the specified number of times
• Fill the left side with 0s
• Update CF, ZF, SF, OF
• The last shifted-out bit → CF

Instruction format

1
shr r/m32, imm8
2
shr r/m64, imm8
3
shr r/m32, cl
4
shr r/m64, cl

Behavioral characteristics

• Does not preserve the sign → not suitable for signed division
• Commonly used for unsigned integers
• Clearly different from SAR (SAR preserves the sign in the highest bit)

Common uses

• Fast division by 2^n (unsigned)
• Bitmask cleanup
• Right-shifting fields in protocol parsing
• Patch points in certain encryption/encoding algorithms