huangmeng
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Embedded_AI


			
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<hr>
<a name="Other-Built_002din-Functions-Provided-by-GCC"></a>
<h3 class="section">6.59 Other Built-in Functions Provided by GCC</h3>
<a name="index-built_002din-functions-1"></a>
<a name="index-_005f_005fbuiltin_005falloca"></a>
<a name="index-_005f_005fbuiltin_005falloca_005fwith_005falign"></a>
<a name="index-_005f_005fbuiltin_005fcall_005fwith_005fstatic_005fchain"></a>
<a name="index-_005f_005fbuiltin_005ffpclassify"></a>
<a name="index-_005f_005fbuiltin_005fisfinite"></a>
<a name="index-_005f_005fbuiltin_005fisnormal"></a>
<a name="index-_005f_005fbuiltin_005fisgreater"></a>
<a name="index-_005f_005fbuiltin_005fisgreaterequal"></a>
<a name="index-_005f_005fbuiltin_005fisinf_005fsign"></a>
<a name="index-_005f_005fbuiltin_005fisless"></a>
<a name="index-_005f_005fbuiltin_005fislessequal"></a>
<a name="index-_005f_005fbuiltin_005fislessgreater"></a>
<a name="index-_005f_005fbuiltin_005fisunordered"></a>
<a name="index-_005f_005fbuiltin_005fpowi"></a>
<a name="index-_005f_005fbuiltin_005fpowif"></a>
<a name="index-_005f_005fbuiltin_005fpowil"></a>
<a name="index-_005fExit"></a>
<a name="index-_005fexit"></a>
<a name="index-abort"></a>
<a name="index-abs"></a>
<a name="index-acos"></a>
<a name="index-acosf"></a>
<a name="index-acosh"></a>
<a name="index-acoshf"></a>
<a name="index-acoshl"></a>
<a name="index-acosl"></a>
<a name="index-alloca"></a>
<a name="index-asin"></a>
<a name="index-asinf"></a>
<a name="index-asinh"></a>
<a name="index-asinhf"></a>
<a name="index-asinhl"></a>
<a name="index-asinl"></a>
<a name="index-atan"></a>
<a name="index-atan2"></a>
<a name="index-atan2f"></a>
<a name="index-atan2l"></a>
<a name="index-atanf"></a>
<a name="index-atanh"></a>
<a name="index-atanhf"></a>
<a name="index-atanhl"></a>
<a name="index-atanl"></a>
<a name="index-bcmp"></a>
<a name="index-bzero"></a>
<a name="index-cabs"></a>
<a name="index-cabsf"></a>
<a name="index-cabsl"></a>
<a name="index-cacos"></a>
<a name="index-cacosf"></a>
<a name="index-cacosh"></a>
<a name="index-cacoshf"></a>
<a name="index-cacoshl"></a>
<a name="index-cacosl"></a>
<a name="index-calloc"></a>
<a name="index-carg"></a>
<a name="index-cargf"></a>
<a name="index-cargl"></a>
<a name="index-casin"></a>
<a name="index-casinf"></a>
<a name="index-casinh"></a>
<a name="index-casinhf"></a>
<a name="index-casinhl"></a>
<a name="index-casinl"></a>
<a name="index-catan"></a>
<a name="index-catanf"></a>
<a name="index-catanh"></a>
<a name="index-catanhf"></a>
<a name="index-catanhl"></a>
<a name="index-catanl"></a>
<a name="index-cbrt"></a>
<a name="index-cbrtf"></a>
<a name="index-cbrtl"></a>
<a name="index-ccos"></a>
<a name="index-ccosf"></a>
<a name="index-ccosh"></a>
<a name="index-ccoshf"></a>
<a name="index-ccoshl"></a>
<a name="index-ccosl"></a>
<a name="index-ceil"></a>
<a name="index-ceilf"></a>
<a name="index-ceill"></a>
<a name="index-cexp"></a>
<a name="index-cexpf"></a>
<a name="index-cexpl"></a>
<a name="index-cimag"></a>
<a name="index-cimagf"></a>
<a name="index-cimagl"></a>
<a name="index-clog"></a>
<a name="index-clogf"></a>
<a name="index-clogl"></a>
<a name="index-clog10"></a>
<a name="index-clog10f"></a>
<a name="index-clog10l"></a>
<a name="index-conj"></a>
<a name="index-conjf"></a>
<a name="index-conjl"></a>
<a name="index-copysign"></a>
<a name="index-copysignf"></a>
<a name="index-copysignl"></a>
<a name="index-cos"></a>
<a name="index-cosf"></a>
<a name="index-cosh"></a>
<a name="index-coshf"></a>
<a name="index-coshl"></a>
<a name="index-cosl"></a>
<a name="index-cpow"></a>
<a name="index-cpowf"></a>
<a name="index-cpowl"></a>
<a name="index-cproj"></a>
<a name="index-cprojf"></a>
<a name="index-cprojl"></a>
<a name="index-creal"></a>
<a name="index-crealf"></a>
<a name="index-creall"></a>
<a name="index-csin"></a>
<a name="index-csinf"></a>
<a name="index-csinh"></a>
<a name="index-csinhf"></a>
<a name="index-csinhl"></a>
<a name="index-csinl"></a>
<a name="index-csqrt"></a>
<a name="index-csqrtf"></a>
<a name="index-csqrtl"></a>
<a name="index-ctan"></a>
<a name="index-ctanf"></a>
<a name="index-ctanh"></a>
<a name="index-ctanhf"></a>
<a name="index-ctanhl"></a>
<a name="index-ctanl"></a>
<a name="index-dcgettext"></a>
<a name="index-dgettext"></a>
<a name="index-drem"></a>
<a name="index-dremf"></a>
<a name="index-dreml"></a>
<a name="index-erf"></a>
<a name="index-erfc"></a>
<a name="index-erfcf"></a>
<a name="index-erfcl"></a>
<a name="index-erff"></a>
<a name="index-erfl"></a>
<a name="index-exit"></a>
<a name="index-exp"></a>
<a name="index-exp10"></a>
<a name="index-exp10f"></a>
<a name="index-exp10l"></a>
<a name="index-exp2"></a>
<a name="index-exp2f"></a>
<a name="index-exp2l"></a>
<a name="index-expf"></a>
<a name="index-expl"></a>
<a name="index-expm1"></a>
<a name="index-expm1f"></a>
<a name="index-expm1l"></a>
<a name="index-fabs"></a>
<a name="index-fabsf"></a>
<a name="index-fabsl"></a>
<a name="index-fdim"></a>
<a name="index-fdimf"></a>
<a name="index-fdiml"></a>
<a name="index-ffs"></a>
<a name="index-floor"></a>
<a name="index-floorf"></a>
<a name="index-floorl"></a>
<a name="index-fma"></a>
<a name="index-fmaf"></a>
<a name="index-fmal"></a>
<a name="index-fmax"></a>
<a name="index-fmaxf"></a>
<a name="index-fmaxl"></a>
<a name="index-fmin"></a>
<a name="index-fminf"></a>
<a name="index-fminl"></a>
<a name="index-fmod"></a>
<a name="index-fmodf"></a>
<a name="index-fmodl"></a>
<a name="index-fprintf"></a>
<a name="index-fprintf_005funlocked"></a>
<a name="index-fputs"></a>
<a name="index-fputs_005funlocked"></a>
<a name="index-frexp"></a>
<a name="index-frexpf"></a>
<a name="index-frexpl"></a>
<a name="index-fscanf"></a>
<a name="index-gamma"></a>
<a name="index-gammaf"></a>
<a name="index-gammal"></a>
<a name="index-gamma_005fr"></a>
<a name="index-gammaf_005fr"></a>
<a name="index-gammal_005fr"></a>
<a name="index-gettext"></a>
<a name="index-hypot"></a>
<a name="index-hypotf"></a>
<a name="index-hypotl"></a>
<a name="index-ilogb"></a>
<a name="index-ilogbf"></a>
<a name="index-ilogbl"></a>
<a name="index-imaxabs"></a>
<a name="index-index"></a>
<a name="index-isalnum"></a>
<a name="index-isalpha"></a>
<a name="index-isascii"></a>
<a name="index-isblank"></a>
<a name="index-iscntrl"></a>
<a name="index-isdigit"></a>
<a name="index-isgraph"></a>
<a name="index-islower"></a>
<a name="index-isprint"></a>
<a name="index-ispunct"></a>
<a name="index-isspace"></a>
<a name="index-isupper"></a>
<a name="index-iswalnum"></a>
<a name="index-iswalpha"></a>
<a name="index-iswblank"></a>
<a name="index-iswcntrl"></a>
<a name="index-iswdigit"></a>
<a name="index-iswgraph"></a>
<a name="index-iswlower"></a>
<a name="index-iswprint"></a>
<a name="index-iswpunct"></a>
<a name="index-iswspace"></a>
<a name="index-iswupper"></a>
<a name="index-iswxdigit"></a>
<a name="index-isxdigit"></a>
<a name="index-j0"></a>
<a name="index-j0f"></a>
<a name="index-j0l"></a>
<a name="index-j1"></a>
<a name="index-j1f"></a>
<a name="index-j1l"></a>
<a name="index-jn"></a>
<a name="index-jnf"></a>
<a name="index-jnl"></a>
<a name="index-labs"></a>
<a name="index-ldexp"></a>
<a name="index-ldexpf"></a>
<a name="index-ldexpl"></a>
<a name="index-lgamma"></a>
<a name="index-lgammaf"></a>
<a name="index-lgammal"></a>
<a name="index-lgamma_005fr"></a>
<a name="index-lgammaf_005fr"></a>
<a name="index-lgammal_005fr"></a>
<a name="index-llabs"></a>
<a name="index-llrint"></a>
<a name="index-llrintf"></a>
<a name="index-llrintl"></a>
<a name="index-llround"></a>
<a name="index-llroundf"></a>
<a name="index-llroundl"></a>
<a name="index-log"></a>
<a name="index-log10"></a>
<a name="index-log10f"></a>
<a name="index-log10l"></a>
<a name="index-log1p"></a>
<a name="index-log1pf"></a>
<a name="index-log1pl"></a>
<a name="index-log2"></a>
<a name="index-log2f"></a>
<a name="index-log2l"></a>
<a name="index-logb"></a>
<a name="index-logbf"></a>
<a name="index-logbl"></a>
<a name="index-logf"></a>
<a name="index-logl"></a>
<a name="index-lrint"></a>
<a name="index-lrintf"></a>
<a name="index-lrintl"></a>
<a name="index-lround"></a>
<a name="index-lroundf"></a>
<a name="index-lroundl"></a>
<a name="index-malloc"></a>
<a name="index-memchr"></a>
<a name="index-memcmp"></a>
<a name="index-memcpy"></a>
<a name="index-mempcpy"></a>
<a name="index-memset"></a>
<a name="index-modf"></a>
<a name="index-modff"></a>
<a name="index-modfl"></a>
<a name="index-nearbyint"></a>
<a name="index-nearbyintf"></a>
<a name="index-nearbyintl"></a>
<a name="index-nextafter"></a>
<a name="index-nextafterf"></a>
<a name="index-nextafterl"></a>
<a name="index-nexttoward"></a>
<a name="index-nexttowardf"></a>
<a name="index-nexttowardl"></a>
<a name="index-pow"></a>
<a name="index-pow10"></a>
<a name="index-pow10f"></a>
<a name="index-pow10l"></a>
<a name="index-powf"></a>
<a name="index-powl"></a>
<a name="index-printf"></a>
<a name="index-printf_005funlocked"></a>
<a name="index-putchar"></a>
<a name="index-puts"></a>
<a name="index-remainder"></a>
<a name="index-remainderf"></a>
<a name="index-remainderl"></a>
<a name="index-remquo"></a>
<a name="index-remquof"></a>
<a name="index-remquol"></a>
<a name="index-rindex"></a>
<a name="index-rint"></a>
<a name="index-rintf"></a>
<a name="index-rintl"></a>
<a name="index-round"></a>
<a name="index-roundf"></a>
<a name="index-roundl"></a>
<a name="index-scalb"></a>
<a name="index-scalbf"></a>
<a name="index-scalbl"></a>
<a name="index-scalbln"></a>
<a name="index-scalblnf"></a>
<a name="index-scalblnf-1"></a>
<a name="index-scalbn"></a>
<a name="index-scalbnf"></a>
<a name="index-scanfnl"></a>
<a name="index-signbit"></a>
<a name="index-signbitf"></a>
<a name="index-signbitl"></a>
<a name="index-signbitd32"></a>
<a name="index-signbitd64"></a>
<a name="index-signbitd128"></a>
<a name="index-significand"></a>
<a name="index-significandf"></a>
<a name="index-significandl"></a>
<a name="index-sin"></a>
<a name="index-sincos"></a>
<a name="index-sincosf"></a>
<a name="index-sincosl"></a>
<a name="index-sinf"></a>
<a name="index-sinh"></a>
<a name="index-sinhf"></a>
<a name="index-sinhl"></a>
<a name="index-sinl"></a>
<a name="index-snprintf"></a>
<a name="index-sprintf"></a>
<a name="index-sqrt"></a>
<a name="index-sqrtf"></a>
<a name="index-sqrtl"></a>
<a name="index-sscanf"></a>
<a name="index-stpcpy"></a>
<a name="index-stpncpy"></a>
<a name="index-strcasecmp"></a>
<a name="index-strcat"></a>
<a name="index-strchr"></a>
<a name="index-strcmp"></a>
<a name="index-strcpy"></a>
<a name="index-strcspn"></a>
<a name="index-strdup"></a>
<a name="index-strfmon"></a>
<a name="index-strftime"></a>
<a name="index-strlen"></a>
<a name="index-strncasecmp"></a>
<a name="index-strncat"></a>
<a name="index-strncmp"></a>
<a name="index-strncpy"></a>
<a name="index-strndup"></a>
<a name="index-strpbrk"></a>
<a name="index-strrchr"></a>
<a name="index-strspn"></a>
<a name="index-strstr"></a>
<a name="index-tan"></a>
<a name="index-tanf"></a>
<a name="index-tanh"></a>
<a name="index-tanhf"></a>
<a name="index-tanhl"></a>
<a name="index-tanl"></a>
<a name="index-tgamma"></a>
<a name="index-tgammaf"></a>
<a name="index-tgammal"></a>
<a name="index-toascii"></a>
<a name="index-tolower"></a>
<a name="index-toupper"></a>
<a name="index-towlower"></a>
<a name="index-towupper"></a>
<a name="index-trunc"></a>
<a name="index-truncf"></a>
<a name="index-truncl"></a>
<a name="index-vfprintf"></a>
<a name="index-vfscanf"></a>
<a name="index-vprintf"></a>
<a name="index-vscanf"></a>
<a name="index-vsnprintf"></a>
<a name="index-vsprintf"></a>
<a name="index-vsscanf"></a>
<a name="index-y0"></a>
<a name="index-y0f"></a>
<a name="index-y0l"></a>
<a name="index-y1"></a>
<a name="index-y1f"></a>
<a name="index-y1l"></a>
<a name="index-yn"></a>
<a name="index-ynf"></a>
<a name="index-ynl"></a>

<p>GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and are not
documented here because they may change from time to time; we do not
recommend general use of these functions.
</p>
<p>The remaining functions are provided for optimization purposes.
</p>
<p>With the exception of built-ins that have library equivalents such as
the standard C library functions discussed below, or that expand to
library calls, GCC built-in functions are always expanded inline and
thus do not have corresponding entry points and their address cannot
be obtained.  Attempting to use them in an expression other than
a function call results in a compile-time error.
</p>
<a name="index-fno_002dbuiltin-3"></a>
<p>GCC includes built-in versions of many of the functions in the standard
C library.  These functions come in two forms: one whose names start with
the <code>__builtin_</code> prefix, and the other without.  Both forms have the
same type (including prototype), the same address (when their address is
taken), and the same meaning as the C library functions even if you specify
the <samp>-fno-builtin</samp> option see <a href="C-Dialect-Options.html#C-Dialect-Options">C Dialect Options</a>).  Many of these
functions are only optimized in certain cases; if they are not optimized in
a particular case, a call to the library function is emitted.
</p>
<a name="index-ansi-2"></a>
<a name="index-std-2"></a>
<p>Outside strict ISO C mode (<samp>-ansi</samp>, <samp>-std=c90</samp>,
<samp>-std=c99</samp> or <samp>-std=c11</samp>), the functions
<code>_exit</code>, <code>alloca</code>, <code>bcmp</code>, <code>bzero</code>,
<code>dcgettext</code>, <code>dgettext</code>, <code>dremf</code>, <code>dreml</code>,
<code>drem</code>, <code>exp10f</code>, <code>exp10l</code>, <code>exp10</code>, <code>ffsll</code>,
<code>ffsl</code>, <code>ffs</code>, <code>fprintf_unlocked</code>,
<code>fputs_unlocked</code>, <code>gammaf</code>, <code>gammal</code>, <code>gamma</code>,
<code>gammaf_r</code>, <code>gammal_r</code>, <code>gamma_r</code>, <code>gettext</code>,
<code>index</code>, <code>isascii</code>, <code>j0f</code>, <code>j0l</code>, <code>j0</code>,
<code>j1f</code>, <code>j1l</code>, <code>j1</code>, <code>jnf</code>, <code>jnl</code>, <code>jn</code>,
<code>lgammaf_r</code>, <code>lgammal_r</code>, <code>lgamma_r</code>, <code>mempcpy</code>,
<code>pow10f</code>, <code>pow10l</code>, <code>pow10</code>, <code>printf_unlocked</code>,
<code>rindex</code>, <code>scalbf</code>, <code>scalbl</code>, <code>scalb</code>,
<code>signbit</code>, <code>signbitf</code>, <code>signbitl</code>, <code>signbitd32</code>,
<code>signbitd64</code>, <code>signbitd128</code>, <code>significandf</code>,
<code>significandl</code>, <code>significand</code>, <code>sincosf</code>,
<code>sincosl</code>, <code>sincos</code>, <code>stpcpy</code>, <code>stpncpy</code>,
<code>strcasecmp</code>, <code>strdup</code>, <code>strfmon</code>, <code>strncasecmp</code>,
<code>strndup</code>, <code>toascii</code>, <code>y0f</code>, <code>y0l</code>, <code>y0</code>,
<code>y1f</code>, <code>y1l</code>, <code>y1</code>, <code>ynf</code>, <code>ynl</code> and
<code>yn</code>
may be handled as built-in functions.
All these functions have corresponding versions
prefixed with <code>__builtin_</code>, which may be used even in strict C90
mode.
</p>
<p>The ISO C99 functions
<code>_Exit</code>, <code>acoshf</code>, <code>acoshl</code>, <code>acosh</code>, <code>asinhf</code>,
<code>asinhl</code>, <code>asinh</code>, <code>atanhf</code>, <code>atanhl</code>, <code>atanh</code>,
<code>cabsf</code>, <code>cabsl</code>, <code>cabs</code>, <code>cacosf</code>, <code>cacoshf</code>,
<code>cacoshl</code>, <code>cacosh</code>, <code>cacosl</code>, <code>cacos</code>,
<code>cargf</code>, <code>cargl</code>, <code>carg</code>, <code>casinf</code>, <code>casinhf</code>,
<code>casinhl</code>, <code>casinh</code>, <code>casinl</code>, <code>casin</code>,
<code>catanf</code>, <code>catanhf</code>, <code>catanhl</code>, <code>catanh</code>,
<code>catanl</code>, <code>catan</code>, <code>cbrtf</code>, <code>cbrtl</code>, <code>cbrt</code>,
<code>ccosf</code>, <code>ccoshf</code>, <code>ccoshl</code>, <code>ccosh</code>, <code>ccosl</code>,
<code>ccos</code>, <code>cexpf</code>, <code>cexpl</code>, <code>cexp</code>, <code>cimagf</code>,
<code>cimagl</code>, <code>cimag</code>, <code>clogf</code>, <code>clogl</code>, <code>clog</code>,
<code>conjf</code>, <code>conjl</code>, <code>conj</code>, <code>copysignf</code>, <code>copysignl</code>,
<code>copysign</code>, <code>cpowf</code>, <code>cpowl</code>, <code>cpow</code>, <code>cprojf</code>,
<code>cprojl</code>, <code>cproj</code>, <code>crealf</code>, <code>creall</code>, <code>creal</code>,
<code>csinf</code>, <code>csinhf</code>, <code>csinhl</code>, <code>csinh</code>, <code>csinl</code>,
<code>csin</code>, <code>csqrtf</code>, <code>csqrtl</code>, <code>csqrt</code>, <code>ctanf</code>,
<code>ctanhf</code>, <code>ctanhl</code>, <code>ctanh</code>, <code>ctanl</code>, <code>ctan</code>,
<code>erfcf</code>, <code>erfcl</code>, <code>erfc</code>, <code>erff</code>, <code>erfl</code>,
<code>erf</code>, <code>exp2f</code>, <code>exp2l</code>, <code>exp2</code>, <code>expm1f</code>,
<code>expm1l</code>, <code>expm1</code>, <code>fdimf</code>, <code>fdiml</code>, <code>fdim</code>,
<code>fmaf</code>, <code>fmal</code>, <code>fmaxf</code>, <code>fmaxl</code>, <code>fmax</code>,
<code>fma</code>, <code>fminf</code>, <code>fminl</code>, <code>fmin</code>, <code>hypotf</code>,
<code>hypotl</code>, <code>hypot</code>, <code>ilogbf</code>, <code>ilogbl</code>, <code>ilogb</code>,
<code>imaxabs</code>, <code>isblank</code>, <code>iswblank</code>, <code>lgammaf</code>,
<code>lgammal</code>, <code>lgamma</code>, <code>llabs</code>, <code>llrintf</code>, <code>llrintl</code>,
<code>llrint</code>, <code>llroundf</code>, <code>llroundl</code>, <code>llround</code>,
<code>log1pf</code>, <code>log1pl</code>, <code>log1p</code>, <code>log2f</code>, <code>log2l</code>,
<code>log2</code>, <code>logbf</code>, <code>logbl</code>, <code>logb</code>, <code>lrintf</code>,
<code>lrintl</code>, <code>lrint</code>, <code>lroundf</code>, <code>lroundl</code>,
<code>lround</code>, <code>nearbyintf</code>, <code>nearbyintl</code>, <code>nearbyint</code>,
<code>nextafterf</code>, <code>nextafterl</code>, <code>nextafter</code>,
<code>nexttowardf</code>, <code>nexttowardl</code>, <code>nexttoward</code>,
<code>remainderf</code>, <code>remainderl</code>, <code>remainder</code>, <code>remquof</code>,
<code>remquol</code>, <code>remquo</code>, <code>rintf</code>, <code>rintl</code>, <code>rint</code>,
<code>roundf</code>, <code>roundl</code>, <code>round</code>, <code>scalblnf</code>,
<code>scalblnl</code>, <code>scalbln</code>, <code>scalbnf</code>, <code>scalbnl</code>,
<code>scalbn</code>, <code>snprintf</code>, <code>tgammaf</code>, <code>tgammal</code>,
<code>tgamma</code>, <code>truncf</code>, <code>truncl</code>, <code>trunc</code>,
<code>vfscanf</code>, <code>vscanf</code>, <code>vsnprintf</code> and <code>vsscanf</code>
are handled as built-in functions
except in strict ISO C90 mode (<samp>-ansi</samp> or <samp>-std=c90</samp>).
</p>
<p>There are also built-in versions of the ISO C99 functions
<code>acosf</code>, <code>acosl</code>, <code>asinf</code>, <code>asinl</code>, <code>atan2f</code>,
<code>atan2l</code>, <code>atanf</code>, <code>atanl</code>, <code>ceilf</code>, <code>ceill</code>,
<code>cosf</code>, <code>coshf</code>, <code>coshl</code>, <code>cosl</code>, <code>expf</code>,
<code>expl</code>, <code>fabsf</code>, <code>fabsl</code>, <code>floorf</code>, <code>floorl</code>,
<code>fmodf</code>, <code>fmodl</code>, <code>frexpf</code>, <code>frexpl</code>, <code>ldexpf</code>,
<code>ldexpl</code>, <code>log10f</code>, <code>log10l</code>, <code>logf</code>, <code>logl</code>,
<code>modfl</code>, <code>modf</code>, <code>powf</code>, <code>powl</code>, <code>sinf</code>,
<code>sinhf</code>, <code>sinhl</code>, <code>sinl</code>, <code>sqrtf</code>, <code>sqrtl</code>,
<code>tanf</code>, <code>tanhf</code>, <code>tanhl</code> and <code>tanl</code>
that are recognized in any mode since ISO C90 reserves these names for
the purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with <code>__builtin_</code>.
</p>
<p>There are also built-in functions <code>__builtin_fabsf<var>n</var></code>,
<code>__builtin_fabsf<var>n</var>x</code>, <code>__builtin_copysignf<var>n</var></code> and
<code>__builtin_copysignf<var>n</var>x</code>, corresponding to the TS 18661-3
functions <code>fabsf<var>n</var></code>, <code>fabsf<var>n</var>x</code>,
<code>copysignf<var>n</var></code> and <code>copysignf<var>n</var>x</code>, for supported
types <code>_Float<var>n</var></code> and <code>_Float<var>n</var>x</code>.
</p>
<p>There are also GNU extension functions <code>clog10</code>, <code>clog10f</code> and
<code>clog10l</code> which names are reserved by ISO C99 for future use.
All these functions have versions prefixed with <code>__builtin_</code>.
</p>
<p>The ISO C94 functions
<code>iswalnum</code>, <code>iswalpha</code>, <code>iswcntrl</code>, <code>iswdigit</code>,
<code>iswgraph</code>, <code>iswlower</code>, <code>iswprint</code>, <code>iswpunct</code>,
<code>iswspace</code>, <code>iswupper</code>, <code>iswxdigit</code>, <code>towlower</code> and
<code>towupper</code>
are handled as built-in functions
except in strict ISO C90 mode (<samp>-ansi</samp> or <samp>-std=c90</samp>).
</p>
<p>The ISO C90 functions
<code>abort</code>, <code>abs</code>, <code>acos</code>, <code>asin</code>, <code>atan2</code>,
<code>atan</code>, <code>calloc</code>, <code>ceil</code>, <code>cosh</code>, <code>cos</code>,
<code>exit</code>, <code>exp</code>, <code>fabs</code>, <code>floor</code>, <code>fmod</code>,
<code>fprintf</code>, <code>fputs</code>, <code>frexp</code>, <code>fscanf</code>,
<code>isalnum</code>, <code>isalpha</code>, <code>iscntrl</code>, <code>isdigit</code>,
<code>isgraph</code>, <code>islower</code>, <code>isprint</code>, <code>ispunct</code>,
<code>isspace</code>, <code>isupper</code>, <code>isxdigit</code>, <code>tolower</code>,
<code>toupper</code>, <code>labs</code>, <code>ldexp</code>, <code>log10</code>, <code>log</code>,
<code>malloc</code>, <code>memchr</code>, <code>memcmp</code>, <code>memcpy</code>,
<code>memset</code>, <code>modf</code>, <code>pow</code>, <code>printf</code>, <code>putchar</code>,
<code>puts</code>, <code>scanf</code>, <code>sinh</code>, <code>sin</code>, <code>snprintf</code>,
<code>sprintf</code>, <code>sqrt</code>, <code>sscanf</code>, <code>strcat</code>,
<code>strchr</code>, <code>strcmp</code>, <code>strcpy</code>, <code>strcspn</code>,
<code>strlen</code>, <code>strncat</code>, <code>strncmp</code>, <code>strncpy</code>,
<code>strpbrk</code>, <code>strrchr</code>, <code>strspn</code>, <code>strstr</code>,
<code>tanh</code>, <code>tan</code>, <code>vfprintf</code>, <code>vprintf</code> and <code>vsprintf</code>
are all recognized as built-in functions unless
<samp>-fno-builtin</samp> is specified (or <samp>-fno-builtin-<var>function</var></samp>
is specified for an individual function).  All of these functions have
corresponding versions prefixed with <code>__builtin_</code>.
</p>
<p>GCC provides built-in versions of the ISO C99 floating-point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( <code>isgreater</code>,
<code>isgreaterequal</code>, <code>isless</code>, <code>islessequal</code>,
<code>islessgreater</code>, and <code>isunordered</code>) , with <code>__builtin_</code>
prefixed.  We intend for a library implementor to be able to simply
<code>#define</code> each standard macro to its built-in equivalent.
In the same fashion, GCC provides <code>fpclassify</code>, <code>isfinite</code>,
<code>isinf_sign</code>, <code>isnormal</code> and <code>signbit</code> built-ins used with
<code>__builtin_</code> prefixed.  The <code>isinf</code> and <code>isnan</code>
built-in functions appear both with and without the <code>__builtin_</code> prefix.
</p>
<dl>
<dt><a name="index-_002a_005f_005fbuiltin_005falloca"></a>Built-in Function: <em>void</em> <strong>*__builtin_alloca</strong> <em>(size_t size)</em></dt>
<dd><p>The <code>__builtin_alloca</code> function must be called at block scope.
The function allocates an object <var>size</var> bytes large on the stack
of the calling function.  The object is aligned on the default stack
alignment boundary for the target determined by the
<code>__BIGGEST_ALIGNMENT__</code> macro.  The <code>__builtin_alloca</code>
function returns a pointer to the first byte of the allocated object.
The lifetime of the allocated object ends just before the calling
function returns to its caller.   This is so even when
<code>__builtin_alloca</code> is called within a nested block.
</p>
<p>For example, the following function allocates eight objects of <code>n</code>
bytes each on the stack, storing a pointer to each in consecutive elements
of the array <code>a</code>.  It then passes the array to function <code>g</code>
which can safely use the storage pointed to by each of the array elements.
</p>
<div class="smallexample">
<pre class="smallexample">void f (unsigned n)
{
  void *a [8];
  for (int i = 0; i != 8; ++i)
    a [i] = __builtin_alloca (n);

  g (a, n);   // <span class="roman">safe</span>
}
</pre></div>

<p>Since the <code>__builtin_alloca</code> function doesn&rsquo;t validate its argument
it is the responsibility of its caller to make sure the argument doesn&rsquo;t
cause it to exceed the stack size limit.
The <code>__builtin_alloca</code> function is provided to make it possible to
allocate on the stack arrays of bytes with an upper bound that may be
computed at run time.  Since C99 Variable Length Arrays offer
similar functionality under a portable, more convenient, and safer
interface they are recommended instead, in both C99 and C++ programs
where GCC provides them as an extension.
See <a href="Variable-Length.html#Variable-Length">Variable Length</a>, for details.
</p>
</dd></dl>

<dl>
<dt><a name="index-_002a_005f_005fbuiltin_005falloca_005fwith_005falign"></a>Built-in Function: <em>void</em> <strong>*__builtin_alloca_with_align</strong> <em>(size_t size, size_t alignment)</em></dt>
<dd><p>The <code>__builtin_alloca_with_align</code> function must be called at block
scope.  The function allocates an object <var>size</var> bytes large on
the stack of the calling function.  The allocated object is aligned on
the boundary specified by the argument <var>alignment</var> whose unit is given
in bits (not bytes).  The <var>size</var> argument must be positive and not
exceed the stack size limit.  The <var>alignment</var> argument must be a constant
integer expression that evaluates to a power of 2 greater than or equal to
<code>CHAR_BIT</code> and less than some unspecified maximum.  Invocations
with other values are rejected with an error indicating the valid bounds.
The function returns a pointer to the first byte of the allocated object.
The lifetime of the allocated object ends at the end of the block in which
the function was called.  The allocated storage is released no later than
just before the calling function returns to its caller, but may be released
at the end of the block in which the function was called.
</p>
<p>For example, in the following function the call to <code>g</code> is unsafe
because when <code>overalign</code> is non-zero, the space allocated by
<code>__builtin_alloca_with_align</code> may have been released at the end
of the <code>if</code> statement in which it was called.
</p>
<div class="smallexample">
<pre class="smallexample">void f (unsigned n, bool overalign)
{
  void *p;
  if (overalign)
    p = __builtin_alloca_with_align (n, 64 /* bits */);
  else
    p = __builtin_alloc (n);

  g (p, n);   // <span class="roman">unsafe</span>
}
</pre></div>

<p>Since the <code>__builtin_alloca_with_align</code> function doesn&rsquo;t validate its
<var>size</var> argument it is the responsibility of its caller to make sure
the argument doesn&rsquo;t cause it to exceed the stack size limit.
The <code>__builtin_alloca_with_align</code> function is provided to make
it possible to allocate on the stack overaligned arrays of bytes with
an upper bound that may be computed at run time.  Since C99
Variable Length Arrays offer the same functionality under
a portable, more convenient, and safer interface they are recommended
instead, in both C99 and C++ programs where GCC provides them as
an extension.  See <a href="Variable-Length.html#Variable-Length">Variable Length</a>, for details.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ftypes_005fcompatible_005fp"></a>Built-in Function: <em>int</em> <strong>__builtin_types_compatible_p</strong> <em>(<var>type1</var>, <var>type2</var>)</em></dt>
<dd>
<p>You can use the built-in function <code>__builtin_types_compatible_p</code> to
determine whether two types are the same.
</p>
<p>This built-in function returns 1 if the unqualified versions of the
types <var>type1</var> and <var>type2</var> (which are types, not expressions) are
compatible, 0 otherwise.  The result of this built-in function can be
used in integer constant expressions.
</p>
<p>This built-in function ignores top level qualifiers (e.g., <code>const</code>,
<code>volatile</code>).  For example, <code>int</code> is equivalent to <code>const
int</code>.
</p>
<p>The type <code>int[]</code> and <code>int[5]</code> are compatible.  On the other
hand, <code>int</code> and <code>char *</code> are not compatible, even if the size
of their types, on the particular architecture are the same.  Also, the
amount of pointer indirection is taken into account when determining
similarity.  Consequently, <code>short *</code> is not similar to
<code>short **</code>.  Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.
</p>
<p>An <code>enum</code> type is not considered to be compatible with another
<code>enum</code> type even if both are compatible with the same integer
type; this is what the C standard specifies.
For example, <code>enum {foo, bar}</code> is not similar to
<code>enum {hot, dog}</code>.
</p>
<p>You typically use this function in code whose execution varies
depending on the arguments&rsquo; types.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">#define foo(x)                                                  \
  ({                                                           \
    typeof (x) tmp = (x);                                       \
    if (__builtin_types_compatible_p (typeof (x), long double)) \
      tmp = foo_long_double (tmp);                              \
    else if (__builtin_types_compatible_p (typeof (x), double)) \
      tmp = foo_double (tmp);                                   \
    else if (__builtin_types_compatible_p (typeof (x), float))  \
      tmp = foo_float (tmp);                                    \
    else                                                        \
      abort ();                                                 \
    tmp;                                                        \
  })
</pre></div>

<p><em>Note:</em> This construct is only available for C.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fcall_005fwith_005fstatic_005fchain-1"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_call_with_static_chain</strong> <em>(<var>call_exp</var>, <var>pointer_exp</var>)</em></dt>
<dd>
<p>The <var>call_exp</var> expression must be a function call, and the
<var>pointer_exp</var> expression must be a pointer.  The <var>pointer_exp</var>
is passed to the function call in the target&rsquo;s static chain location.
The result of builtin is the result of the function call.
</p>
<p><em>Note:</em> This builtin is only available for C.
This builtin can be used to call Go closures from C.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fchoose_005fexpr"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_choose_expr</strong> <em>(<var>const_exp</var>, <var>exp1</var>, <var>exp2</var>)</em></dt>
<dd>
<p>You can use the built-in function <code>__builtin_choose_expr</code> to
evaluate code depending on the value of a constant expression.  This
built-in function returns <var>exp1</var> if <var>const_exp</var>, which is an
integer constant expression, is nonzero.  Otherwise it returns <var>exp2</var>.
</p>
<p>This built-in function is analogous to the &lsquo;<samp>? :</samp>&rsquo; operator in C,
except that the expression returned has its type unaltered by promotion
rules.  Also, the built-in function does not evaluate the expression
that is not chosen.  For example, if <var>const_exp</var> evaluates to true,
<var>exp2</var> is not evaluated even if it has side-effects.
</p>
<p>This built-in function can return an lvalue if the chosen argument is an
lvalue.
</p>
<p>If <var>exp1</var> is returned, the return type is the same as <var>exp1</var>&rsquo;s
type.  Similarly, if <var>exp2</var> is returned, its return type is the same
as <var>exp2</var>.
</p>
<p>Example:
</p>
<div class="smallexample">
<pre class="smallexample">#define foo(x)                                                    \
  __builtin_choose_expr (                                         \
    __builtin_types_compatible_p (typeof (x), double),            \
    foo_double (x),                                               \
    __builtin_choose_expr (                                       \
      __builtin_types_compatible_p (typeof (x), float),           \
      foo_float (x),                                              \
      /* <span class="roman">The void expression results in a compile-time error</span>  \
         <span class="roman">when assigning the result to something.</span>  */          \
      (void)0))
</pre></div>

<p><em>Note:</em> This construct is only available for C.  Furthermore, the
unused expression (<var>exp1</var> or <var>exp2</var> depending on the value of
<var>const_exp</var>) may still generate syntax errors.  This may change in
future revisions.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fcomplex"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_complex</strong> <em>(<var>real</var>, <var>imag</var>)</em></dt>
<dd>
<p>The built-in function <code>__builtin_complex</code> is provided for use in
implementing the ISO C11 macros <code>CMPLXF</code>, <code>CMPLX</code> and
<code>CMPLXL</code>.  <var>real</var> and <var>imag</var> must have the same type, a
real binary floating-point type, and the result has the corresponding
complex type with real and imaginary parts <var>real</var> and <var>imag</var>.
Unlike &lsquo;<samp><var>real</var> + I * <var>imag</var></samp>&rsquo;, this works even when
infinities, NaNs and negative zeros are involved.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fconstant_005fp"></a>Built-in Function: <em>int</em> <strong>__builtin_constant_p</strong> <em>(<var>exp</var>)</em></dt>
<dd><p>You can use the built-in function <code>__builtin_constant_p</code> to
determine if a value is known to be constant at compile time and hence
that GCC can perform constant-folding on expressions involving that
value.  The argument of the function is the value to test.  The function
returns the integer 1 if the argument is known to be a compile-time
constant and 0 if it is not known to be a compile-time constant.  A
return of 0 does not indicate that the value is <em>not</em> a constant,
but merely that GCC cannot prove it is a constant with the specified
value of the <samp>-O</samp> option.
</p>
<p>You typically use this function in an embedded application where
memory is a critical resource.  If you have some complex calculation,
you may want it to be folded if it involves constants, but need to call
a function if it does not.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">#define Scale_Value(X)      \
  (__builtin_constant_p (X) \
  ? ((X) * SCALE + OFFSET) : Scale (X))
</pre></div>

<p>You may use this built-in function in either a macro or an inline
function.  However, if you use it in an inlined function and pass an
argument of the function as the argument to the built-in, GCC 
never returns 1 when you call the inline function with a string constant
or compound literal (see <a href="Compound-Literals.html#Compound-Literals">Compound Literals</a>) and does not return 1
when you pass a constant numeric value to the inline function unless you
specify the <samp>-O</samp> option.
</p>
<p>You may also use <code>__builtin_constant_p</code> in initializers for static
data.  For instance, you can write
</p>
<div class="smallexample">
<pre class="smallexample">static const int table[] = {
   __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
   /* <span class="roman">&hellip;</span> */
};
</pre></div>

<p>This is an acceptable initializer even if <var>EXPRESSION</var> is not a
constant expression, including the case where
<code>__builtin_constant_p</code> returns 1 because <var>EXPRESSION</var> can be
folded to a constant but <var>EXPRESSION</var> contains operands that are
not otherwise permitted in a static initializer (for example,
<code>0 &amp;&amp; foo ()</code>).  GCC must be more conservative about evaluating the
built-in in this case, because it has no opportunity to perform
optimization.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fexpect"></a>Built-in Function: <em>long</em> <strong>__builtin_expect</strong> <em>(long <var>exp</var>, long <var>c</var>)</em></dt>
<dd><a name="index-fprofile_002darcs-1"></a>
<p>You may use <code>__builtin_expect</code> to provide the compiler with
branch prediction information.  In general, you should prefer to
use actual profile feedback for this (<samp>-fprofile-arcs</samp>), as
programmers are notoriously bad at predicting how their programs
actually perform.  However, there are applications in which this
data is hard to collect.
</p>
<p>The return value is the value of <var>exp</var>, which should be an integral
expression.  The semantics of the built-in are that it is expected that
<var>exp</var> == <var>c</var>.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">if (__builtin_expect (x, 0))
  foo ();
</pre></div>

<p>indicates that we do not expect to call <code>foo</code>, since
we expect <code>x</code> to be zero.  Since you are limited to integral
expressions for <var>exp</var>, you should use constructions such as
</p>
<div class="smallexample">
<pre class="smallexample">if (__builtin_expect (ptr != NULL, 1))
  foo (*ptr);
</pre></div>

<p>when testing pointer or floating-point values.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ftrap"></a>Built-in Function: <em>void</em> <strong>__builtin_trap</strong> <em>(void)</em></dt>
<dd><p>This function causes the program to exit abnormally.  GCC implements
this function by using a target-dependent mechanism (such as
intentionally executing an illegal instruction) or by calling
<code>abort</code>.  The mechanism used may vary from release to release so
you should not rely on any particular implementation.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005funreachable"></a>Built-in Function: <em>void</em> <strong>__builtin_unreachable</strong> <em>(void)</em></dt>
<dd><p>If control flow reaches the point of the <code>__builtin_unreachable</code>,
the program is undefined.  It is useful in situations where the
compiler cannot deduce the unreachability of the code.
</p>
<p>One such case is immediately following an <code>asm</code> statement that
either never terminates, or one that transfers control elsewhere
and never returns.  In this example, without the
<code>__builtin_unreachable</code>, GCC issues a warning that control
reaches the end of a non-void function.  It also generates code
to return after the <code>asm</code>.
</p>
<div class="smallexample">
<pre class="smallexample">int f (int c, int v)
{
  if (c)
    {
      return v;
    }
  else
    {
      asm(&quot;jmp error_handler&quot;);
      __builtin_unreachable ();
    }
}
</pre></div>

<p>Because the <code>asm</code> statement unconditionally transfers control out
of the function, control never reaches the end of the function
body.  The <code>__builtin_unreachable</code> is in fact unreachable and
communicates this fact to the compiler.
</p>
<p>Another use for <code>__builtin_unreachable</code> is following a call a
function that never returns but that is not declared
<code>__attribute__((noreturn))</code>, as in this example:
</p>
<div class="smallexample">
<pre class="smallexample">void function_that_never_returns (void);

int g (int c)
{
  if (c)
    {
      return 1;
    }
  else
    {
      function_that_never_returns ();
      __builtin_unreachable ();
    }
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fassume_005faligned"></a>Built-in Function: <em>void *</em> <strong>__builtin_assume_aligned</strong> <em>(const void *<var>exp</var>, size_t <var>align</var>, ...)</em></dt>
<dd><p>This function returns its first argument, and allows the compiler
to assume that the returned pointer is at least <var>align</var> bytes
aligned.  This built-in can have either two or three arguments,
if it has three, the third argument should have integer type, and
if it is nonzero means misalignment offset.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">void *x = __builtin_assume_aligned (arg, 16);
</pre></div>

<p>means that the compiler can assume <code>x</code>, set to <code>arg</code>, is at least
16-byte aligned, while:
</p>
<div class="smallexample">
<pre class="smallexample">void *x = __builtin_assume_aligned (arg, 32, 8);
</pre></div>

<p>means that the compiler can assume for <code>x</code>, set to <code>arg</code>, that
<code>(char *) x - 8</code> is 32-byte aligned.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fLINE"></a>Built-in Function: <em>int</em> <strong>__builtin_LINE</strong> <em>()</em></dt>
<dd><p>This function is the equivalent of the preprocessor <code>__LINE__</code>
macro and returns a constant integer expression that evaluates to
the line number of the invocation of the built-in.  When used as a C++
default argument for a function <var>F</var>, it returns the line number
of the call to <var>F</var>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fFUNCTION"></a>Built-in Function: <em>const char *</em> <strong>__builtin_FUNCTION</strong> <em>()</em></dt>
<dd><p>This function is the equivalent of the <code>__FUNCTION__</code> symbol
and returns an address constant pointing to the name of the function
from which the built-in was invoked, or the empty string if
the invocation is not at function scope.  When used as a C++ default
argument for a function <var>F</var>, it returns the name of <var>F</var>&rsquo;s
caller or the empty string if the call was not made at function
scope.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fFILE"></a>Built-in Function: <em>const char *</em> <strong>__builtin_FILE</strong> <em>()</em></dt>
<dd><p>This function is the equivalent of the preprocessor <code>__FILE__</code>
macro and returns an address constant pointing to the file name
containing the invocation of the built-in, or the empty string if
the invocation is not at function scope.  When used as a C++ default
argument for a function <var>F</var>, it returns the file name of the call
to <var>F</var> or the empty string if the call was not made at function
scope.
</p>
<p>For example, in the following, each call to function <code>foo</code> will
print a line similar to <code>&quot;file.c:123: foo: message&quot;</code> with the name
of the file and the line number of the <code>printf</code> call, the name of
the function <code>foo</code>, followed by the word <code>message</code>.
</p>
<div class="smallexample">
<pre class="smallexample">const char*
function (const char *func = __builtin_FUNCTION ())
{
  return func;
}

void foo (void)
{
  printf (&quot;%s:%i: %s: message\n&quot;, file (), line (), function ());
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fclear_005fcache"></a>Built-in Function: <em>void</em> <strong>__builtin___clear_cache</strong> <em>(char *<var>begin</var>, char *<var>end</var>)</em></dt>
<dd><p>This function is used to flush the processor&rsquo;s instruction cache for
the region of memory between <var>begin</var> inclusive and <var>end</var>
exclusive.  Some targets require that the instruction cache be
flushed, after modifying memory containing code, in order to obtain
deterministic behavior.
</p>
<p>If the target does not require instruction cache flushes,
<code>__builtin___clear_cache</code> has no effect.  Otherwise either
instructions are emitted in-line to clear the instruction cache or a
call to the <code>__clear_cache</code> function in libgcc is made.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fprefetch"></a>Built-in Function: <em>void</em> <strong>__builtin_prefetch</strong> <em>(const void *<var>addr</var>, ...)</em></dt>
<dd><p>This function is used to minimize cache-miss latency by moving data into
a cache before it is accessed.
You can insert calls to <code>__builtin_prefetch</code> into code for which
you know addresses of data in memory that is likely to be accessed soon.
If the target supports them, data prefetch instructions are generated.
If the prefetch is done early enough before the access then the data will
be in the cache by the time it is accessed.
</p>
<p>The value of <var>addr</var> is the address of the memory to prefetch.
There are two optional arguments, <var>rw</var> and <var>locality</var>.
The value of <var>rw</var> is a compile-time constant one or zero; one
means that the prefetch is preparing for a write to the memory address
and zero, the default, means that the prefetch is preparing for a read.
The value <var>locality</var> must be a compile-time constant integer between
zero and three.  A value of zero means that the data has no temporal
locality, so it need not be left in the cache after the access.  A value
of three means that the data has a high degree of temporal locality and
should be left in all levels of cache possible.  Values of one and two
mean, respectively, a low or moderate degree of temporal locality.  The
default is three.
</p>
<div class="smallexample">
<pre class="smallexample">for (i = 0; i &lt; n; i++)
  {
    a[i] = a[i] + b[i];
    __builtin_prefetch (&amp;a[i+j], 1, 1);
    __builtin_prefetch (&amp;b[i+j], 0, 1);
    /* <span class="roman">&hellip;</span> */
  }
</pre></div>

<p>Data prefetch does not generate faults if <var>addr</var> is invalid, but
the address expression itself must be valid.  For example, a prefetch
of <code>p-&gt;next</code> does not fault if <code>p-&gt;next</code> is not a valid
address, but evaluation faults if <code>p</code> is not a valid address.
</p>
<p>If the target does not support data prefetch, the address expression
is evaluated if it includes side effects but no other code is generated
and GCC does not issue a warning.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fval"></a>Built-in Function: <em>double</em> <strong>__builtin_huge_val</strong> <em>(void)</em></dt>
<dd><p>Returns a positive infinity, if supported by the floating-point format,
else <code>DBL_MAX</code>.  This function is suitable for implementing the
ISO C macro <code>HUGE_VAL</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fvalf"></a>Built-in Function: <em>float</em> <strong>__builtin_huge_valf</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return type is <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fvall"></a>Built-in Function: <em>long double</em> <strong>__builtin_huge_vall</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return
type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-n"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>__builtin_huge_valf<var>n</var> (void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return type is
<code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-1"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>x __builtin_huge_valf<var>n</var>x (void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return type is
<code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ffpclassify-1"></a>Built-in Function: <em>int</em> <strong>__builtin_fpclassify</strong> <em>(int, int, int, int, int, ...)</em></dt>
<dd><p>This built-in implements the C99 fpclassify functionality.  The first
five int arguments should be the target library&rsquo;s notion of the
possible FP classes and are used for return values.  They must be
constant values and they must appear in this order: <code>FP_NAN</code>,
<code>FP_INFINITE</code>, <code>FP_NORMAL</code>, <code>FP_SUBNORMAL</code> and
<code>FP_ZERO</code>.  The ellipsis is for exactly one floating-point value
to classify.  GCC treats the last argument as type-generic, which
means it does not do default promotion from float to double.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finf"></a>Built-in Function: <em>double</em> <strong>__builtin_inf</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except a warning is generated
if the target floating-point format does not support infinities.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfd32"></a>Built-in Function: <em>_Decimal32</em> <strong>__builtin_infd32</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>_Decimal32</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfd64"></a>Built-in Function: <em>_Decimal64</em> <strong>__builtin_infd64</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>_Decimal64</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfd128"></a>Built-in Function: <em>_Decimal128</em> <strong>__builtin_infd128</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>_Decimal128</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finff"></a>Built-in Function: <em>float</em> <strong>__builtin_inff</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>float</code>.
This function is suitable for implementing the ISO C99 macro <code>INFINITY</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfl"></a>Built-in Function: <em>long double</em> <strong>__builtin_infl</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return
type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-2"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>__builtin_inff<var>n</var> (void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return
type is <code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-3"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>__builtin_inff<var>n</var>x (void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return
type is <code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fisinf_005fsign-1"></a>Built-in Function: <em>int</em> <strong>__builtin_isinf_sign</strong> <em>(...)</em></dt>
<dd><p>Similar to <code>isinf</code>, except the return value is -1 for
an argument of <code>-Inf</code> and 1 for an argument of <code>+Inf</code>.
Note while the parameter list is an
ellipsis, this function only accepts exactly one floating-point
argument.  GCC treats this parameter as type-generic, which means it
does not do default promotion from float to double.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnan"></a>Built-in Function: <em>double</em> <strong>__builtin_nan</strong> <em>(const char *str)</em></dt>
<dd><p>This is an implementation of the ISO C99 function <code>nan</code>.
</p>
<p>Since ISO C99 defines this function in terms of <code>strtod</code>, which we
do not implement, a description of the parsing is in order.  The string
is parsed as by <code>strtol</code>; that is, the base is recognized by
leading &lsquo;<samp>0</samp>&rsquo; or &lsquo;<samp>0x</samp>&rsquo; prefixes.  The number parsed is placed
in the significand such that the least significant bit of the number
is at the least significant bit of the significand.  The number is
truncated to fit the significand field provided.  The significand is
forced to be a quiet NaN.
</p>
<p>This function, if given a string literal all of which would have been
consumed by <code>strtol</code>, is evaluated early enough that it is considered a
compile-time constant.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnand32"></a>Built-in Function: <em>_Decimal32</em> <strong>__builtin_nand32</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>_Decimal32</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnand64"></a>Built-in Function: <em>_Decimal64</em> <strong>__builtin_nand64</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>_Decimal64</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnand128"></a>Built-in Function: <em>_Decimal128</em> <strong>__builtin_nand128</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>_Decimal128</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnanf"></a>Built-in Function: <em>float</em> <strong>__builtin_nanf</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnanl"></a>Built-in Function: <em>long double</em> <strong>__builtin_nanl</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-4"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>__builtin_nanf<var>n</var> (const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is
<code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-5"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>x __builtin_nanf<var>n</var>x (const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is
<code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnans"></a>Built-in Function: <em>double</em> <strong>__builtin_nans</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the significand is forced
to be a signaling NaN.  The <code>nans</code> function is proposed by
<a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm">WG14 N965</a>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnansf"></a>Built-in Function: <em>float</em> <strong>__builtin_nansf</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnansl"></a>Built-in Function: <em>long double</em> <strong>__builtin_nansl</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-6"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>__builtin_nansf<var>n</var> (const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is
<code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-n-7"></a>Built-in Function: <em>_Float</em> <strong><var>n</var></strong> <em>x __builtin_nansf<var>n</var>x (const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is
<code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fffs"></a>Built-in Function: <em>int</em> <strong>__builtin_ffs</strong> <em>(int x)</em></dt>
<dd><p>Returns one plus the index of the least significant 1-bit of <var>x</var>, or
if <var>x</var> is zero, returns zero.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclz"></a>Built-in Function: <em>int</em> <strong>__builtin_clz</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the number of leading 0-bits in <var>x</var>, starting at the most
significant bit position.  If <var>x</var> is 0, the result is undefined.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fctz"></a>Built-in Function: <em>int</em> <strong>__builtin_ctz</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the number of trailing 0-bits in <var>x</var>, starting at the least
significant bit position.  If <var>x</var> is 0, the result is undefined.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclrsb"></a>Built-in Function: <em>int</em> <strong>__builtin_clrsb</strong> <em>(int x)</em></dt>
<dd><p>Returns the number of leading redundant sign bits in <var>x</var>, i.e. the
number of bits following the most significant bit that are identical
to it.  There are no special cases for 0 or other values. 
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpopcount"></a>Built-in Function: <em>int</em> <strong>__builtin_popcount</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the number of 1-bits in <var>x</var>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fparity"></a>Built-in Function: <em>int</em> <strong>__builtin_parity</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the parity of <var>x</var>, i.e. the number of 1-bits in <var>x</var>
modulo 2.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fffsl"></a>Built-in Function: <em>int</em> <strong>__builtin_ffsl</strong> <em>(long)</em></dt>
<dd><p>Similar to <code>__builtin_ffs</code>, except the argument type is
<code>long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclzl"></a>Built-in Function: <em>int</em> <strong>__builtin_clzl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_clz</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fctzl"></a>Built-in Function: <em>int</em> <strong>__builtin_ctzl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_ctz</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclrsbl"></a>Built-in Function: <em>int</em> <strong>__builtin_clrsbl</strong> <em>(long)</em></dt>
<dd><p>Similar to <code>__builtin_clrsb</code>, except the argument type is
<code>long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpopcountl"></a>Built-in Function: <em>int</em> <strong>__builtin_popcountl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_popcount</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fparityl"></a>Built-in Function: <em>int</em> <strong>__builtin_parityl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_parity</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fffsll"></a>Built-in Function: <em>int</em> <strong>__builtin_ffsll</strong> <em>(long long)</em></dt>
<dd><p>Similar to <code>__builtin_ffs</code>, except the argument type is
<code>long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclzll"></a>Built-in Function: <em>int</em> <strong>__builtin_clzll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_clz</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fctzll"></a>Built-in Function: <em>int</em> <strong>__builtin_ctzll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_ctz</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclrsbll"></a>Built-in Function: <em>int</em> <strong>__builtin_clrsbll</strong> <em>(long long)</em></dt>
<dd><p>Similar to <code>__builtin_clrsb</code>, except the argument type is
<code>long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpopcountll"></a>Built-in Function: <em>int</em> <strong>__builtin_popcountll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_popcount</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fparityll"></a>Built-in Function: <em>int</em> <strong>__builtin_parityll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_parity</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpowi-1"></a>Built-in Function: <em>double</em> <strong>__builtin_powi</strong> <em>(double, int)</em></dt>
<dd><p>Returns the first argument raised to the power of the second.  Unlike the
<code>pow</code> function no guarantees about precision and rounding are made.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpowif-1"></a>Built-in Function: <em>float</em> <strong>__builtin_powif</strong> <em>(float, int)</em></dt>
<dd><p>Similar to <code>__builtin_powi</code>, except the argument and return types
are <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpowil-1"></a>Built-in Function: <em>long double</em> <strong>__builtin_powil</strong> <em>(long double, int)</em></dt>
<dd><p>Similar to <code>__builtin_powi</code>, except the argument and return types
are <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fbswap16"></a>Built-in Function: <em>uint16_t</em> <strong>__builtin_bswap16</strong> <em>(uint16_t x)</em></dt>
<dd><p>Returns <var>x</var> with the order of the bytes reversed; for example,
<code>0xaabb</code> becomes <code>0xbbaa</code>.  Byte here always means
exactly 8 bits.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fbswap32"></a>Built-in Function: <em>uint32_t</em> <strong>__builtin_bswap32</strong> <em>(uint32_t x)</em></dt>
<dd><p>Similar to <code>__builtin_bswap16</code>, except the argument and return types
are 32 bit.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fbswap64"></a>Built-in Function: <em>uint64_t</em> <strong>__builtin_bswap64</strong> <em>(uint64_t x)</em></dt>
<dd><p>Similar to <code>__builtin_bswap32</code>, except the argument and return types
are 64 bit.
</p></dd></dl>

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