Intel 64 and IA-32 Architectures Software Developers Manual Volume 2A, Instruction Set Reference, A-M

3-12 Vol. 2
INSTRUCTION SET REFERENCE, A-M
3.1.1.8 Intel® C/C++ Compiler Intrinsics Equivalents Section
The Intel C/C++ compiler intrinsics equivalents are special C/C++ coding extensions
that allow using the syntax of C function calls and C variables instead of hardware
registers. Using these intrinsics frees programmers from having to manage registers
and assembly programming. Further, the compiler optimizes the instruction sched-
uling so that executable run faster.
The following sections discuss the intrinsics API and the MMX technology and SIMD
floating-point intrinsics. Each intrinsic equivalent is listed with the instruction
description. There may be additional intrinsics that do not have an instruction equiv-
alent. It is strongly recommended that the reader reference the compiler documen-
tation for the complete list of supported intrinsics.
See Appendix C, “InteL® C/C++ Compiler Intrinsics and Functional Equivalents,” in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B, for
more information on using intrinsics.
The Intrinsics API
The benefit of coding with MMX technology intrinsics and the SSE/SSE2/SSE3 intrin-
sics is that you can use the syntax of C function calls and C variables instead of hard-
ware registers. This frees you from managing registers and programming assembly.
Further, the compiler optimizes the instruction scheduling so that your executable
runs faster. For each computational and data manipulation instruction in the new
instruction set, there is a corresponding C intrinsic that implements it directly. The
intrinsics allow you to specify the underlying implementation (instruction selection)
of an algorithm yet leave instruction scheduling and register allocation to the
compiler.
MMX
™
Technology Intrinsics
The MMX technology intrinsics are based on a __m64 data type that represents the
specific contents of an MMX technology register. You can specify values in bytes,
short integers, 32-bit values, or a 64-bit object. The __m64 data type, however, is
not a basic ANSI C data type, and therefore you must observe the following usage
restrictions:
• Use __m64 data only on the left-hand side of an assignment, as a return value,
or as a parameter. You cannot use it with other arithmetic expressions (“+”, “>>”,
and so on).
• Use __m64 objects in aggregates, such as unions to access the byte elements
and structures; the address of an __m64 object may be taken.
• Use __m64 data only with the MMX technology intrinsics described in this manual
and Intel
®
C/C++ compiler documentation.
• See:
— http://www.intel.com/support/performancetools/