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Intrinsic function

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</style><div role="note" class="hatnote navigation-not-searchable">This article is about compiler intrinsic functions. For X toolkit, see <a href="X_Toolkit_Intrinsics" title="X Toolkit Intrinsics">X Toolkit Intrinsics</a>.</div>

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In <a href="Software" title="Software">computer software</a>, in compiler theory, an intrinsic function, also called built-in function or builtin function, is a function (<a href="Subroutine" class="mw-redirect" title="Subroutine">subroutine</a>) available for use in a given <a href="Programming_language" title="Programming language">programming language</a> whose implementation is handled specially by the <a href="Compiler" title="Compiler">compiler</a>. Typically, it may substitute a sequence of automatically generated <a href="Instruction_set_architecture" title="Instruction set architecture">instructions</a> for the original function call, similar to an <a href="Inline_function" class="mw-redirect" title="Inline function">inline function</a>.<a href="#cite_note-IntelCompilerIntrinsics-1">[1]</a> Unlike an inline function, the compiler has an intimate knowledge of an intrinsic function and can thus better integrate and optimize it for a given situation.

Compilers that implement intrinsic functions may enable them only when a program requests <a href="Optimizing_compiler" title="Optimizing compiler">optimization</a>, otherwise falling back to a default implementation provided by the language <a href="Runtime_system" title="Runtime system">runtime system</a> (environment).

<div class="mw-heading mw-heading2"><h2 id="Vectorization_and_parallelization">Vectorization and parallelization</h2></div>

Intrinsic functions are often used to explicitly implement <a href="Automatic_vectorization" title="Automatic vectorization">vectorization</a> and <a href="Automatic_parallelization" title="Automatic parallelization">parallelization</a> in languages which do not address such constructs. Some <a href="Application_programming_interface" class="mw-redirect" title="Application programming interface">application programming interfaces</a> (API), for example, <a href="AltiVec" title="AltiVec">AltiVec</a> and <a href="OpenMP" title="OpenMP">OpenMP</a>, use intrinsic functions to declare, respectively, vectorizable and <a href="Multiprocessing" title="Multiprocessing">multiprocessing</a>-aware operations during compiling. The compiler parses the intrinsic functions and converts them into vector math or multiprocessing <a href="Object_code" title="Object code">object code</a> appropriate for the target <a href="Platform_(computing)" class="mw-redirect" title="Platform (computing)">platform</a>.

Some intrinsics are used to provide additional constraints to the optimizer, such as values a variable cannot assume.<a href="#cite_note-2">[2]</a>

<div class="mw-heading mw-heading2"><h2 id="By_programming_language">By programming language</h2></div>

Compilers for <a href="C_(programming_language)" title="C (programming language)">C</a> and <a href="C%2B%2B" title="C++">C++</a>, of Microsoft,<a href="#cite_note-3">[3]</a>

Intel,<a href="#cite_note-IntelCompilerIntrinsics-1">[1]</a> and the <a href="GNU_Compiler_Collection" title="GNU Compiler Collection">GNU Compiler Collection</a> (GCC)<a href="#cite_note-4">[4]</a>

implement intrinsics that map directly to the <a href="X86" title="X86">x86</a> single instruction, multiple data (<a href="SIMD" class="mw-redirect" title="SIMD">SIMD</a>) instructions (<a href="MMX_(instruction_set)" title="MMX (instruction set)">MMX</a>, <a href="Streaming_SIMD_Extensions" title="Streaming SIMD Extensions">Streaming SIMD Extensions</a> (SSE), <a href="SSE2" title="SSE2">SSE2</a>, <a href="SSE3" title="SSE3">SSE3</a>, <a href="SSSE3" title="SSSE3">SSSE3</a>, <a href="SSE4" title="SSE4">SSE4</a>, <a href="Advanced_Vector_Extensions" title="Advanced Vector Extensions">AVX</a>, <a href="AVX2" class="mw-redirect" title="AVX2">AVX2</a>, <a href="AVX512" class="mw-redirect" title="AVX512">AVX512</a>, <a href="FMA_instruction_set" title="FMA instruction set">FMA</a>, ...). Intrinsics allow mapping to standard assembly instructions that are not normally accessible through C/C++; e.g. bit scan and parallel operations on <a href="Streaming_SIMD_Extensions" title="Streaming SIMD Extensions">128 bits</a> and <a href="Advanced_Vector_Extensions" title="Advanced Vector Extensions">256 bits</a>.

Some C and C++ compilers provide non-portable platform-specific intrinsics. Other intrinsics (such as <a href="GNU_Compiler_Collection" title="GNU Compiler Collection">GNU</a> built-ins) are slightly more abstracted, approximating the abilities of several contemporary platforms, with portable fall back implementations on platforms with no appropriate instructions.<a href="#cite_note-5">[5]</a> It is common for C++ libraries, such as glm or <a href="Sony" title="Sony">Sony</a>'s <a href="Glossary_of_computer_graphics#V" title="Glossary of computer graphics">vector maths libraries</a>,<a href="#cite_note-6">[6]</a> to achieve portability via <a href="Conditional_compilation" title="Conditional compilation">conditional compilation</a> (based on platform specific compiler flags), providing fully portable high-level primitives (e.g., a four-element floating-point vector type) mapped onto the appropriate <a href="Low_level_programming_language" class="mw-redirect" title="Low level programming language">low level programming language</a> implementations, while still benefiting from the C++ type system and inlining; hence the advantage over linking to hand-written assembly object files, using the C <a href="Application_binary_interface" title="Application binary interface">application binary interface</a> (ABI).

<div class="mw-heading mw-heading4"><h4 id="Examples">Examples</h4></div>

The following are examples of signatures of intrinsic functions from Intel's set of intrinsic functions.

<div style="font-size:78%;" class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre> uint64_t __rdtsc (); // return internal CPU clock counter

uint64_t __popcnt64 (uint64_t n); // count of bits set in n

uint64_t _umul128 (uint64_t Factor1, uint64_t Factor2, uint64_t* HighProduct); // 64 bit * 64 bit => 128 bit multiplication

__m512 _mm512_add_ps (__m512 a, __m512 b); // calculates a + b for two vectors of 16 floats

__m512 _mm512_fmadd_ps(__m512 a, __m512 b, __m512 c); // calculates a*b + c for three vectors of 16 floats

</pre></div><a href="#cite_note-7">[7]</a>

The <a href="HotSpot_(virtual_machine)" title="HotSpot (virtual machine)">HotSpot</a> <a href="Java_virtual_machine" title="Java virtual machine">Java virtual machine</a>'s (JVM) <a href="Just-in-time_compilation" title="Just-in-time compilation">just-in-time compiler</a> also has intrinsics for specific Java APIs.<a href="#cite_note-8">[8]</a> Hotspot intrinsics are standard Java APIs which may have one or more optimized implementation on some platforms.

ANSI/ISO <a href="PL/I" title="PL/I">PL/I</a> defines nearly 90 builtin functions.<a href="#cite_note-ANSI-9">[9]</a> These are conventionally grouped as follows:<a href="#cite_note-PLI1.1-10">[10]</a>: 337–338

<ul><li>String-handling builtin functions such as INDEX, LENGTH</li>

<li>Arithmetic builtin functions such as ABS, CEIL, ROUND</li>

<li>Mathematical builtin functions like SIN, COS, LOG, ERF</li>

<li>Array-handling builtin functions, for example ANY, ALL, PROD</li>

<li>Condition-handling builtin functions like ONCODE, ONFILE</li>

<li>Storage Control builtin functions, for example ADDR, POINTER</li>

<li>Input-Output builtins: LINENO</li>

<li>Miscellaneous builtin functions like DATE and TIME</li></ul>

Individual compilers have added additional builtins specific to a machine architecture or operating system.

A builtin function is identified by leaving its name undeclared and allowing it to default, or by declaring it <code>BUILTIN</code>. A user-supplied function of the same name can be substituted by declaring it as <code>ENTRY</code>.

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://software.intel.com/en-us/cpp-compiler-developer-guide-and-reference-intrinsics">"Intel® C++ Compiler 19.1 Developer Guide and Reference"</a>. Intel® C++ Compiler Documentation. 16 December 2019. Retrieved 2020-01-17.</cite>

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<li id="cite_note-2"><a href="#cite_ref-2">^</a> <cite id="CITEREFThe_Clang_Team2020" class="citation web cs1">The Clang Team (2020). <a rel="nofollow" class="external text" href="https://clang.llvm.org/docs/LanguageExtensions.html#builtin-assume">"Clang Language Extensions"</a>. Clang 11 documentation. Retrieved 2020-01-17. <q>Builtin Functions</q></cite>

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<cite id="CITEREFMSDN" class="citation web cs1"><a href="Microsoft_Developer_Network" title="Microsoft Developer Network">MSDN</a>. <a rel="nofollow" class="external text" href="http://msdn.Microsoft.com/en-us/library/26td21ds">"Compiler Intrinsics"</a>. <a href="Microsoft" title="Microsoft">Microsoft</a>. Retrieved 2012-06-20.</cite>

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<cite id="CITEREFGCC_documentation" class="citation web cs1">GCC documentation. <a rel="nofollow" class="external text" href="https://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html">"Built-in Functions Specific to Particular Target Machines"</a>. <a href="Free_Software_Foundation" title="Free Software Foundation">Free Software Foundation</a>. Retrieved 2012-06-20.</cite>

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<li id="cite_note-5"><a href="#cite_ref-5">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html">"Vector Extensions"</a>. Using the GNU Compiler Collection (GCC). Retrieved 2020-01-16.</cite>

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<li id="cite_note-6"><a href="#cite_ref-6">^</a> <cite class="citation news cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160624183718/https://forum.beyond3d.com/threads/sony-open-sources-vector-math-and-simd-math-libraries-cell-ppu-spu-other-platforms.38677/">"Sony open sources Vector Math and SIMD math libraries (Cell PPU/SPU/other platforms)"</a>. Beyond3D Forum. Archived from <a rel="nofollow" class="external text" href="https://forum.beyond3d.com/threads/sony-open-sources-vector-math-and-simd-math-libraries-cell-ppu-spu-other-platforms.38677/">the original</a> on 2016-06-24. Retrieved 2020-01-17.</cite>

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<li id="cite_note-7"><a href="#cite_ref-7">^</a> <a rel="nofollow" class="external text" href="https://software.intel.com/sites/landingpage/IntrinsicsGuide/">Intel Intrinsics</a>

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<li id="cite_note-8"><a href="#cite_ref-8">^</a> <cite id="CITEREFMok2013" class="citation web cs1">Mok, Kris (25 February 2013). <a rel="nofollow" class="external text" href="https://www.slideshare.net/RednaxelaFX/green-teajug-hotspotintrinsics02232013">"Intrinsic Methods in HotSpot VM"</a>. Slideshare. Retrieved 2014-12-20.</cite>

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<li id="cite_note-ANSI-9"><a href="#cite_ref-ANSI_9-0">^</a> <cite id="CITEREFANSI_X3_Committee1976" class="citation book cs1">ANSI X3 Committee (1976). American National Standard programming language PL/I.</cite><code class="cs1-code">{{cite book}}</code>: CS1 maint: numeric names: authors list (link)

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<li id="cite_note-PLI1.1-10"><a href="#cite_ref-PLI1.1_10-0">^</a> <cite id="CITEREFIBM_Corporation1995" class="citation book cs1">IBM Corporation (1995). IBM PL/I for MVS & VM Language Reference.</cite>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="https://software.intel.com/sites/landingpage/IntrinsicsGuide/">Intel Intrinsics Guide</a></li>

<li><a rel="nofollow" class="external text" href="https://www-01.ibm.com/support/knowledgecenter/ssw_aix_61/com.ibm.aix.alangref/idalangref_milicode_routines.htm">Using milicode routines</a>, IBM AIX 6.1 documentation</li></ul></div><div><div class="zim-footer">

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