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Chapter 4 Instruction-Decoding Optimizations 87
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
4.10 8-Bit Sign-Extended Immediate Values
Optimization
Use 8-bit sign-extended immediate values instead of larger-size values.
Application
This optimization applies to:
• 32-bit software
• 64-bit software
Rationale
Using 8-bit sign-extended immediate values improves code density with no negative affects on the
processor.
Example
Consider this instruction:
add bx, -5
Avoid encoding it as:
81 C3 FF FB
Instead, encode it as:
83 C3 FB