To ensure portability of applications optimized to exploit the SIMD functions of POWER ISA processors, the ELF V2 ABI defines a set of functions and data types for SIMD programming. ELF V2-compliant compilers will provide suitable support for these functions, preferably as built-in functions that translate to one or more POWER ISA instructions. Compilers are encouraged, but not required, to provide built-in functions to access individual instructions in the IBM POWER® instruction set architecture. In most cases, each such built-in function should provide direct access to the underlying instruction. However, to ease porting between little-endian (LE) and big-endian (BE) POWER systems, and between POWER and other platforms, it is preferable that some built-in functions provide the same semantics on both LE and BE POWER systems, even if this means that the built-in functions are implemented with different instruction sequences for LE and BE. To achieve this, vector built-in functions provide a set of functions derived from the set of hardware functions provided by the Power vector SIMD instructions. Unlike traditional “hardware intrinsic” built-in functions, no fixed mapping exists between these built-in functions and the generated hardware instruction sequence. Rather, the compiler is free to generate optimized instruction sequences that implement the semantics of the program specified by the programmer using these built-in functions. This is primarily applicable to the POWER SIMD instructions. As we've seen, this set of instructions operates on groups of 2, 4, 8, or 16 vector elements at a time in 128-bit registers. On a big-endian POWER platform, vector elements are loaded from memory into a register so that the 0th element occupies the high-order bits of the register, and the (N – 1)th element occupies the low-order bits of the register. This is referred to as big-endian element order. On a little-endian POWER platform, vector elements are loaded from memory such that the 0th element occupies the low-order bits of the register, and the (N – 1)th element occupies the high-order bits. This is referred to as little-endian element order.

Languages provide support for the data types in to represent vector data types stored in vector registers. For the C and C++ programming languages (and related/derived languages), these data types may be accessed based on the type names listed in when Power ISA SIMD language extensions are enabled using either the vector or __vector keywords. NOTE THAT THIS IS THE FIRST TIME WE'VE MENTIONED THESE LANGUAGE EXTENSIONS, NEED TO FIX THAT. For the Fortran language, OH YET ANOTHER STINKING TABLE gives a correspondence between Fortran and C/C++ language types. The assignment operator always performs a byte-by-byte data copy for vector data types. Like other C/C++ language types, vector types may be defined to have const or volatile properties. Vector data types can be defined as being in static, auto, and register storage. Pointers to vector types are defined like pointers of other C/C++ types. Pointers to vector objects may be defined to have const and volatile properties. Pointers to vector objects must be divisible by 16, as vector objects are always aligned on quadword (128-bit) boundaries. The preferred way to access vectors at an application-defined address is by using vector pointers and the C/C++ dereference operator *. Similar to other C/C++ data types, the array reference operator [] may be used to access vector objects with a vector pointer with the usual definition to access the nth vector element from a vector pointer. The dereference operator * may not be used to access data that is not aligned at least to a quadword boundary. Built-in functions such as vec_xl and vec_xst are provided for unaligned data access. Compilers are expected to recognize and optimize multiple operations that can be optimized into a single hardware instruction. For example, a load and splat hardware instruction might be generated for the following sequence: double *double_ptr; register vector double vd = vec_splats(*double_ptr); Power SIMD C Types sizeof Alignment Description vector unsigned char 16 Quadword Vector of 16 unsigned bytes. vector signed char 16 Quadword Vector of 16 signed bytes. vector bool char 16 Quadword Vector of 16 bytes with a value of either 0 or 28 – 1. vector unsigned short 16 Quadword Vector of 8 unsigned halfwords. vector signed short 16 Quadword Vector of 8 signed halfwords. vector bool short 16 Quadword Vector of 8 halfwords with a value of either 0 or 216 – 1. vector unsigned int 16 Quadword Vector of 4 unsigned words. vector signed int 16 Quadword Vector of 4 signed words. vector bool int 16 Quadword Vector of 4 words with a value of either 0 or 232 – 1. vector unsigned long The vector long types are deprecated due to their ambiguity between 32-bit and 64-bit environments. The use of the vector long long types is preferred. vector unsigned long long 16 Quadword Vector of 2 unsigned doublewords. vector signed long vector signed long long 16 Quadword Vector of 2 signed doublewords. vector bool long vector bool long long 16 Quadword Vector of 2 doublewords with a value of either 0 or 264 – 1. vector unsigned __int128 16 Quadword Vector of 1 unsigned quadword. vector signed __int128 16 Quadword Vector of 1 signed quadword. vector _Float16 16 Quadword Vector of 8 half-precision floats. vector float 16 Quadword Vector of 4 single-precision floats. vector double 16 Quadword Vector of 2 double-precision floats.

In addition to the dereference and assignment operators, the Power SIMD Vector Programming API (REALLY?) provides the usual operators that are valid on pointers; these operators are also valid for pointers to vector types. The traditional C/C++ operators are defined on vector types with “do all” semantics for unary and binary +, unary and binary –, binary *, binary %, and binary / as well as the unary and binary shift, logical and comparison operators, and the ternary ?: operator. For unary operators, the specified operation is performed on the corresponding base element of the single operand to derive the result value for each vector element of the vector result. The result type of unary operations is the type of the single input operand. For binary operators, the specified operation is performed on the corresponding base elements of both operands to derive the result value for each vector element of the vector result. Both operands of the binary operators must have the same vector type with the same base element type. The result of binary operators is the same type as the type of the input operands. Further, the array reference operator may be applied to vector data types, yielding an l-value corresponding to the specified element in accordance with the vector element numbering rules (see ). An l-value may either be assigned a new value or accessed for reading its value.

filler

filler

vec_sld vec_perm