ranjith kumar wrote:
Hi,
I wrote a c program which uses functions and data
types defined in xmmintrin.h.
Suprisingly, in assembly code, produced by gcc, each
function call is replaced by a single assembly
instruction.
What is the special about functions defined in
xmmintrin.h.
How they are compiled by gcc?
Any answers or any matirial?
Thanks in advance.
These intrinsics were developed as a way of programming at a lower
level, without being tied exclusively to one instruction set or
assembler syntax. So, the code should be portable between commercial
compilers and gcc, and between 32-bit/x86-64/ia64. They also provide a
way to optimize by use of parallel instructions, in situations where
vectorization doesn't work, or when a less capable compiler is in use.
Not that I would use them as a way of persuading gcc-3.2 or MSVC to do
what gcc-4.3 does by auto-vectorization.
You could learn a lot about them simply by studying xmmintrin.h. The
gcc version is more readable than the commercial ones, but they have
much the same content. To some extent, it's a way of automatically
changing asm macros when you change target platforms, within the
implemented range, as well as providing an alternative to each
programmer inventing new wheels.
Google will give you some hints about additional reading material. It
doesn't matter whether you use the Windows or linux oriented articles.
