Programming-Guides/Intrinsics_Reference/ch_intro.xml

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<chapter version="5.0" xml:lang="en" xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="section_intro">
  
  <!-- Chapter Title goes here. -->
  <title>Introduction to Vector Programming on POWER</title>

  <section>
    <title>A Brief History</title>
    <para>
      The history of vector programming on POWER processors begins
      with the AIM (Apple, IBM, Motorola) alliance in the 1990s.  The
      AIM partners developed the Power Vector Media Extension (VMX) to
      accelerate multimedia applications, particularly image
      processing.  VMX is the name still used by IBM for this
      instruction set.  Freescale (formerly Motorola) used the
      trademark "AltiVec," while Apple at one time called it "Velocity
      Engine."  While VMX remains the most official name, the term
      AltiVec is still in common use today.  Freescale's AltiVec
      Technology Programming Interface Manual (the "AltiVec PIM") is
      still available online for reference (see <xref
      linkend="VIPR.intro.links" />).
    </para>
    <para>
      The original VMX specification provided for thirty-two 128-bit
      vector registers (VRs).  Each register can be treated as
      containing sixteen 8-bit character values, eight 16-bit short
      integer values, four 32-bit integer values, or four 32-bit
      single-precision floating-point values (the "VMX data types").
      Furthermore, the integer data types have signed, unsigned, and
      boolean variants.  An extensive set of arithmetic, logical,
      comparison, conversion, memory access, and permute class
      operations were specified to operate on these registers.
    </para>
    <para>
      The AltiVec PIM documents intrinsic functions to be used by
      programmers to access the VMX instruction set.  Because similar
      operations are provided for all the VMX data types, the PIM
      provides for overloaded intrinsics that can operate on different
      data types.  However, such function overloading is not normally
      acceptable in the C programming language, so compilers compliant
      with the AltiVec PIM (such as <code>gcc</code> and
      <code>clang</code>) were required to add special handling to
      their parsers to permit this.  The PIM suggested (but did not
      mandate) the use of a header file,
      <code>&lt;altivec.h&gt;</code>, for implementations that provide
      AltiVec intrinsics.  This is common practice for all compliant
      compilers today.
    </para>
    <para>
      The first chips incorporating the VMX instruction set were
      introduced by Freescale in 1999, and used primarly in Apple
      desktop computers.  IBM's last desktop CPU (the PowerPC 970)
      also included AltiVec support, and was used in the Apple
      PowerMac G5.  IBM initially omitted support for VMX from its
      server-class computers, but added support for it in the POWER6
      server family.
    </para>
    <para>
      Next talk about VSX introduced for P7.  Changes in registers and
      types.
    </para>
    <section>
      <title>Little-Endian Linux</title>
      <para>
	Yes, it caused a lot of problems.  See chapter on this.
      </para>
    </section>
  </section>

  <section>
    <title>The Unified Vector Register Set</title>
    <para>filler</para>
  </section>

  <section xml:id="VIPR.intro.links">
    <title>Useful Links</title>
    <para>filler</para>
  </section>

</chapter>