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| Previous: <a rel="previous" accesskey="p" href="FP-Comparison-Functions.html#FP-Comparison-Functions">FP Comparison Functions</a>, |
| Up: <a rel="up" accesskey="u" href="Arithmetic-Functions.html#Arithmetic-Functions">Arithmetic Functions</a> |
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| <h4 class="subsection">20.8.7 Miscellaneous FP arithmetic functions</h4> |
| |
| <p><a name="index-minimum-2503"></a><a name="index-maximum-2504"></a><a name="index-positive-difference-2505"></a><a name="index-multiply_002dadd-2506"></a> |
| The functions in this section perform miscellaneous but common |
| operations that are awkward to express with C operators. On some |
| processors these functions can use special machine instructions to |
| perform these operations faster than the equivalent C code. |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>fmin</b> (<var>double x, double y</var>)<var><a name="index-fmin-2507"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>fminf</b> (<var>float x, float y</var>)<var><a name="index-fminf-2508"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>fminl</b> (<var>long double x, long double y</var>)<var><a name="index-fminl-2509"></a></var><br> |
| <blockquote><p>The <code>fmin</code> function returns the lesser of the two values <var>x</var> |
| and <var>y</var>. It is similar to the expression |
| <pre class="smallexample"> ((x) < (y) ? (x) : (y)) |
| </pre> |
| <p>except that <var>x</var> and <var>y</var> are only evaluated once. |
| |
| <p>If an argument is NaN, the other argument is returned. If both arguments |
| are NaN, NaN is returned. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>fmax</b> (<var>double x, double y</var>)<var><a name="index-fmax-2510"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>fmaxf</b> (<var>float x, float y</var>)<var><a name="index-fmaxf-2511"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>fmaxl</b> (<var>long double x, long double y</var>)<var><a name="index-fmaxl-2512"></a></var><br> |
| <blockquote><p>The <code>fmax</code> function returns the greater of the two values <var>x</var> |
| and <var>y</var>. |
| |
| <p>If an argument is NaN, the other argument is returned. If both arguments |
| are NaN, NaN is returned. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>fdim</b> (<var>double x, double y</var>)<var><a name="index-fdim-2513"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>fdimf</b> (<var>float x, float y</var>)<var><a name="index-fdimf-2514"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>fdiml</b> (<var>long double x, long double y</var>)<var><a name="index-fdiml-2515"></a></var><br> |
| <blockquote><p>The <code>fdim</code> function returns the positive difference between |
| <var>x</var> and <var>y</var>. The positive difference is <var>x</var> - |
| <var>y</var> if <var>x</var> is greater than <var>y</var>, and 0 otherwise. |
| |
| <p>If <var>x</var>, <var>y</var>, or both are NaN, NaN is returned. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>fma</b> (<var>double x, double y, double z</var>)<var><a name="index-fma-2516"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>fmaf</b> (<var>float x, float y, float z</var>)<var><a name="index-fmaf-2517"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>fmal</b> (<var>long double x, long double y, long double z</var>)<var><a name="index-fmal-2518"></a></var><br> |
| <blockquote><p><a name="index-butterfly-2519"></a>The <code>fma</code> function performs floating-point multiply-add. This is |
| the operation (<var>x</var> &middot; <var>y</var>) + <var>z</var>, but the |
| intermediate result is not rounded to the destination type. This can |
| sometimes improve the precision of a calculation. |
| |
| <p>This function was introduced because some processors have a special |
| instruction to perform multiply-add. The C compiler cannot use it |
| directly, because the expression ‘<samp><span class="samp">x*y + z</span></samp>’ is defined to round the |
| intermediate result. <code>fma</code> lets you choose when you want to round |
| only once. |
| |
| <p><a name="index-FP_005fFAST_005fFMA-2520"></a>On processors which do not implement multiply-add in hardware, |
| <code>fma</code> can be very slow since it must avoid intermediate rounding. |
| <samp><span class="file">math.h</span></samp> defines the symbols <code>FP_FAST_FMA</code>, |
| <code>FP_FAST_FMAF</code>, and <code>FP_FAST_FMAL</code> when the corresponding |
| version of <code>fma</code> is no slower than the expression ‘<samp><span class="samp">x*y + z</span></samp>’. |
| In the GNU C library, this always means the operation is implemented in |
| hardware. |
| </p></blockquote></div> |
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