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7.13.24 PowerPC AltiVec/VSX Built-in Functions ¶

GCC provides an interface for the PowerPC family of processors to accessthe AltiVec operations described in Motorola’s AltiVec ProgrammingInterface Manual. The interface is made available by including<altivec.h> and using-maltivec and-mabi=altivec. The interface supports the following vectortypes.

vector unsigned charvector signed charvector bool charvector unsigned shortvector signed shortvector bool shortvector pixelvector unsigned intvector signed intvector bool intvector float

GCC’s implementation of the high-level language interface available fromC and C++ code differs from Motorola’s documentation in several ways.

• A vector constant is a list of constant expressions within curly braces.
• A vector initializer requires no cast if the vector constant is of thesame type as the variable it is initializing.
• Ifsigned orunsigned is omitted, the signedness of thevector type is the default signedness of the base type. The defaultvaries depending on the operating system, so a portable program shouldalways specify the signedness.
• Compiling with-maltivec adds keywords__vector,vector,__pixel,pixel,__bool andbool. When compiling ISO C, the context-sensitive substitutionof the keywordsvector,pixel andbool isdisabled. To use them, you must include<altivec.h> instead.
• GCC allows using atypedef name as the type specifier for avector type, but only under the following circumstances:
  • When using__vector instead ofvector; for example,

    typedef signed short int16;__vector int16 data;

  • When usingvector in keyword-and-predefine mode; for example,

    typedef signed short int16;vector int16 data;

    Note that keyword-and-predefine mode is enabled by disabling GNUextensions (e.g., by using-std=c11) and including<altivec.h>.

• For C, overloaded functions are implemented with macros so the followingdoes not work:

    vec_add ((vector signed int){1, 2, 3, 4}, foo);

  Sincevec_add is a macro, the vector constant in the exampleis treated as four separate arguments. Wrap the entire argument inparentheses for this to work.

Note: Only the<altivec.h> interface is supported.Internally, GCC uses built-in functions to achieve the functionality inthe aforementioned header file, but they are not supported and aresubject to change without notice.

GCC complies with the Power Vector Intrinsic Programming Reference (PVIPR),which may be found athttps://openpowerfoundation.org/?resource_lib=power-vector-intrinsic-programming-reference.Chapter 4 of this document fully documents the vector API interfacesthat must beprovided by compliant compilers. Programmers should preferentially usethe interfaces described therein. However, historically GCC has providedadditional interfaces for access to vector instructions. These arebriefly described below. Where the PVIPR provides a portable interface,other functions in GCC that provide the same capabilities should beconsidered deprecated.

The PVIPR documents the following overloaded functions:

• PowerPC AltiVec Built-in Functions on ISA 2.05
• PowerPC AltiVec Built-in Functions Available on ISA 2.06
• PowerPC AltiVec Built-in Functions Available on ISA 2.07
• PowerPC AltiVec Built-in Functions Available on ISA 3.0
• PowerPC AltiVec Built-in Functions Available on ISA 3.1

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