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diff --git a/devdocs/c/numeric%2Ffenv%2Ffeclearexcept.html b/devdocs/c/numeric%2Ffenv%2Ffeclearexcept.html new file mode 100644 index 00000000..04dbc3ee --- /dev/null +++ b/devdocs/c/numeric%2Ffenv%2Ffeclearexcept.html @@ -0,0 +1,63 @@ + <h1 id="firstHeading" class="firstHeading">feclearexcept</h1> <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code><fenv.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">int feclearexcept( int excepts );</pre> +</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> </table> <p>Attempts to clear the floating-point exceptions that are listed in the bitmask argument <code>excepts</code>, which is a bitwise OR of the <a href="fe_exceptions" title="c/numeric/fenv/FE exceptions">floating-point exception macros</a>.</p> +<h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> excepts </td> <td> - </td> <td> bitmask listing the exception flags to clear </td> +</tr> +</table> <h3 id="Return_value"> Return value</h3> <p><code>0</code> if all indicated exceptions were successfully cleared or if <code>excepts</code> is zero. Returns a non-zero value on error.</p> +<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <fenv.h> +#include <stdio.h> +#include <math.h> +#include <float.h> + +/* + * A possible implementation of hypot which makes use of many advanced + * floating-point features. + */ +double hypot_demo(double a, double b) { + const int range_problem = FE_OVERFLOW | FE_UNDERFLOW; + feclearexcept(range_problem); + // try a fast algorithm + double result = sqrt(a * a + b * b); + if (!fetestexcept(range_problem)) // no overflow or underflow + return result; // return the fast result + // do a more complicated calculation to avoid overflow or underflow + int a_exponent,b_exponent; + frexp(a, &a_exponent); + frexp(b, &b_exponent); + + if (a_exponent - b_exponent > DBL_MAX_EXP) + return fabs(a) + fabs(b); // we can ignore the smaller value + // scale so that fabs(a) is near 1 + double a_scaled = scalbn(a, -a_exponent); + double b_scaled = scalbn(b, -a_exponent); + // overflow and underflow is now impossible + result = sqrt(a_scaled * a_scaled + b_scaled * b_scaled); + // undo scaling + return scalbn(result, a_exponent); +} + +int main(void) +{ + // Normal case takes the fast route + printf("hypot(%f, %f) = %f\n", 3.0, 4.0, hypot_demo(3.0, 4.0)); + // Extreme case takes the slow but more accurate route + printf("hypot(%e, %e) = %e\n", DBL_MAX / 2.0, + DBL_MAX / 2.0, + hypot_demo(DBL_MAX / 2.0, DBL_MAX / 2.0)); + + return 0; +}</pre></div> <p>Output:</p> +<div class="text source-text"><pre data-language="c">hypot(3.000000, 4.000000) = 5.000000 +hypot(8.988466e+307, 8.988466e+307) = 1.271161e+308</pre></div> </div> <h3 id="References"> References</h3> <ul> +<li> C11 standard (ISO/IEC 9899:2011): </li> +<ul><li> 7.6.2.1 The feclearexcept function (p: 209) </li></ul> +<li> C99 standard (ISO/IEC 9899:1999): </li> +<ul><li> 7.6.2.1 The feclearexcept function (p: 190) </li></ul> +</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="fetestexcept" title="c/numeric/fenv/fetestexcept"> <span class="t-lines"><span>fetestexcept</span></span></a></div> +<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> determines which of the specified floating-point status flags are set <br> <span class="t-mark">(function)</span> </td> +</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/numeric/fenv/feclearexcept" title="cpp/numeric/fenv/feclearexcept">C++ documentation</a></span> for <code>feclearexcept</code> </td> +</tr> </table> <div class="_attribution"> + <p class="_attribution-p"> + © cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br> + <a href="https://en.cppreference.com/w/c/numeric/fenv/feclearexcept" class="_attribution-link">https://en.cppreference.com/w/c/numeric/fenv/feclearexcept</a> + </p> +</div> |