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| <h4 class="subsection">20.8.3 Rounding Functions</h4> |
| |
| <p><a name="index-converting-floats-to-integers-2437"></a> |
| <a name="index-math_002eh-2438"></a>The functions listed here perform operations such as rounding and |
| truncation of floating-point values. Some of these functions convert |
| floating point numbers to integer values. They are all declared in |
| <samp><span class="file">math.h</span></samp>. |
| |
| <p>You can also convert floating-point numbers to integers simply by |
| casting them to <code>int</code>. This discards the fractional part, |
| effectively rounding towards zero. However, this only works if the |
| result can actually be represented as an <code>int</code>—for very large |
| numbers, this is impossible. The functions listed here return the |
| result as a <code>double</code> instead to get around this problem. |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>ceil</b> (<var>double x</var>)<var><a name="index-ceil-2439"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>ceilf</b> (<var>float x</var>)<var><a name="index-ceilf-2440"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>ceill</b> (<var>long double x</var>)<var><a name="index-ceill-2441"></a></var><br> |
| <blockquote><p>These functions round <var>x</var> upwards to the nearest integer, |
| returning that value as a <code>double</code>. Thus, <code>ceil (1.5)</code> |
| is <code>2.0</code>. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>floor</b> (<var>double x</var>)<var><a name="index-floor-2442"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>floorf</b> (<var>float x</var>)<var><a name="index-floorf-2443"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>floorl</b> (<var>long double x</var>)<var><a name="index-floorl-2444"></a></var><br> |
| <blockquote><p>These functions round <var>x</var> downwards to the nearest |
| integer, returning that value as a <code>double</code>. Thus, <code>floor |
| (1.5)</code> is <code>1.0</code> and <code>floor (-1.5)</code> is <code>-2.0</code>. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>trunc</b> (<var>double x</var>)<var><a name="index-trunc-2445"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>truncf</b> (<var>float x</var>)<var><a name="index-truncf-2446"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>truncl</b> (<var>long double x</var>)<var><a name="index-truncl-2447"></a></var><br> |
| <blockquote><p>The <code>trunc</code> functions round <var>x</var> towards zero to the nearest |
| integer (returned in floating-point format). Thus, <code>trunc (1.5)</code> |
| is <code>1.0</code> and <code>trunc (-1.5)</code> is <code>-1.0</code>. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>rint</b> (<var>double x</var>)<var><a name="index-rint-2448"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>rintf</b> (<var>float x</var>)<var><a name="index-rintf-2449"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>rintl</b> (<var>long double x</var>)<var><a name="index-rintl-2450"></a></var><br> |
| <blockquote><p>These functions round <var>x</var> to an integer value according to the |
| current rounding mode. See <a href="Floating-Point-Parameters.html#Floating-Point-Parameters">Floating Point Parameters</a>, for |
| information about the various rounding modes. The default |
| rounding mode is to round to the nearest integer; some machines |
| support other modes, but round-to-nearest is always used unless |
| you explicitly select another. |
| |
| <p>If <var>x</var> was not initially an integer, these functions raise the |
| inexact exception. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>nearbyint</b> (<var>double x</var>)<var><a name="index-nearbyint-2451"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>nearbyintf</b> (<var>float x</var>)<var><a name="index-nearbyintf-2452"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>nearbyintl</b> (<var>long double x</var>)<var><a name="index-nearbyintl-2453"></a></var><br> |
| <blockquote><p>These functions return the same value as the <code>rint</code> functions, but |
| do not raise the inexact exception if <var>x</var> is not an integer. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>round</b> (<var>double x</var>)<var><a name="index-round-2454"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>roundf</b> (<var>float x</var>)<var><a name="index-roundf-2455"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>roundl</b> (<var>long double x</var>)<var><a name="index-roundl-2456"></a></var><br> |
| <blockquote><p>These functions are similar to <code>rint</code>, but they round halfway |
| cases away from zero instead of to the nearest integer (or other |
| current rounding mode). |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: long int <b>lrint</b> (<var>double x</var>)<var><a name="index-lrint-2457"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long int <b>lrintf</b> (<var>float x</var>)<var><a name="index-lrintf-2458"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long int <b>lrintl</b> (<var>long double x</var>)<var><a name="index-lrintl-2459"></a></var><br> |
| <blockquote><p>These functions are just like <code>rint</code>, but they return a |
| <code>long int</code> instead of a floating-point number. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: long long int <b>llrint</b> (<var>double x</var>)<var><a name="index-llrint-2460"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long long int <b>llrintf</b> (<var>float x</var>)<var><a name="index-llrintf-2461"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long long int <b>llrintl</b> (<var>long double x</var>)<var><a name="index-llrintl-2462"></a></var><br> |
| <blockquote><p>These functions are just like <code>rint</code>, but they return a |
| <code>long long int</code> instead of a floating-point number. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: long int <b>lround</b> (<var>double x</var>)<var><a name="index-lround-2463"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long int <b>lroundf</b> (<var>float x</var>)<var><a name="index-lroundf-2464"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long int <b>lroundl</b> (<var>long double x</var>)<var><a name="index-lroundl-2465"></a></var><br> |
| <blockquote><p>These functions are just like <code>round</code>, but they return a |
| <code>long int</code> instead of a floating-point number. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: long long int <b>llround</b> (<var>double x</var>)<var><a name="index-llround-2466"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long long int <b>llroundf</b> (<var>float x</var>)<var><a name="index-llroundf-2467"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long long int <b>llroundl</b> (<var>long double x</var>)<var><a name="index-llroundl-2468"></a></var><br> |
| <blockquote><p>These functions are just like <code>round</code>, but they return a |
| <code>long long int</code> instead of a floating-point number. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>modf</b> (<var>double value, double *integer-part</var>)<var><a name="index-modf-2469"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>modff</b> (<var>float value, float *integer-part</var>)<var><a name="index-modff-2470"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>modfl</b> (<var>long double value, long double *integer-part</var>)<var><a name="index-modfl-2471"></a></var><br> |
| <blockquote><p>These functions break the argument <var>value</var> into an integer part and a |
| fractional part (between <code>-1</code> and <code>1</code>, exclusive). Their sum |
| equals <var>value</var>. Each of the parts has the same sign as <var>value</var>, |
| and the integer part is always rounded toward zero. |
| |
| <p><code>modf</code> stores the integer part in <code>*</code><var>integer-part</var>, and |
| returns the fractional part. For example, <code>modf (2.5, &intpart)</code> |
| returns <code>0.5</code> and stores <code>2.0</code> into <code>intpart</code>. |
| </p></blockquote></div> |
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