Introduction to AltiVec/SSE Migration Guide

AltiVec/SSE Migration Guide will assist experienced developers who need to migrate their vector-oriented code from the PowerPC AltiVec extensions to the Intel x86 SSE extensions. Both of these are sets of SIMD (single instruction, multiple data) instructions, accessible through C intrinsics. The instructions operate on special sets of 128-bit registers that can be used to hold vectors of smaller-sized data, to be operated on in parallel.

The two sets of instructions serve the same purposes, but are implemented differently; porting of algorithms from one to the other must be done carefully.

Most work involving vector-oriented calculations can be done via Apple’s Accelerate frameworks, which provide higher-level functions for image processing, signal processing, linear algebra, vector math, and operations on large numbers. The advantage of using these frameworks is that the hardware dependencies are abstracted away by highly optimized library code that will be maintained not only for PowerPC and Apple’s initial Intel processors, but also for future processors.

Developers who have already written AltiVec code should consider adopting the Accelerate frameworks, instead of porting to SSE. However, some developers will need to port their code, or to write new AltiVec and SSE versions of new algorithms. Similarly, those who are porting Windows applications to Mac OS X may need to port existing SSE code to AltiVec.

Who Should Read This Document

Any developer who needs to port existing AltiVec code to SSE or vice versa, or who needs to write custom-optimized code for both architectures.

Organization of This Document

This document is organized into the following chapters:


The document assumes the following:


The term x86 is a generic term used in some parts of this book to refer to the class of microprocessors manufactured by Intel. This book uses the term x86 as a synonym for IA-32 (Intel Architecture 32-bit).