Справочник Пользователя для AMD 250
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.
processor.
Example
Consider this instruction:
add bx, -5
Avoid encoding it as:
81 C3 FF FB
Instead, encode it as:
83 C3 FB