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| <h3 class="section">20.4 Floating-Point Number Classification Functions</h3> |
| |
| <p><a name="index-floating_002dpoint-classes-2338"></a><a name="index-classes_002c-floating_002dpoint-2339"></a><a name="index-math_002eh-2340"></a> |
| ISO C99<!-- /@w --> defines macros that let you determine what sort of |
| floating-point number a variable holds. |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>fpclassify</b> (<em>float-type</em><var> x</var>)<var><a name="index-fpclassify-2341"></a></var><br> |
| <blockquote><p>This is a generic macro which works on all floating-point types and |
| which returns a value of type <code>int</code>. The possible values are: |
| |
| <dl> |
| <dt><code>FP_NAN</code><a name="index-FP_005fNAN-2342"></a><dd>The floating-point number <var>x</var> is “Not a Number” (see <a href="Infinity-and-NaN.html#Infinity-and-NaN">Infinity and NaN</a>) |
| <br><dt><code>FP_INFINITE</code><a name="index-FP_005fINFINITE-2343"></a><dd>The value of <var>x</var> is either plus or minus infinity (see <a href="Infinity-and-NaN.html#Infinity-and-NaN">Infinity and NaN</a>) |
| <br><dt><code>FP_ZERO</code><a name="index-FP_005fZERO-2344"></a><dd>The value of <var>x</var> is zero. In floating-point formats like IEEE 754<!-- /@w -->, where zero can be signed, this value is also returned if |
| <var>x</var> is negative zero. |
| <br><dt><code>FP_SUBNORMAL</code><a name="index-FP_005fSUBNORMAL-2345"></a><dd>Numbers whose absolute value is too small to be represented in the |
| normal format are represented in an alternate, <dfn>denormalized</dfn> format |
| (see <a href="Floating-Point-Concepts.html#Floating-Point-Concepts">Floating Point Concepts</a>). This format is less precise but can |
| represent values closer to zero. <code>fpclassify</code> returns this value |
| for values of <var>x</var> in this alternate format. |
| <br><dt><code>FP_NORMAL</code><a name="index-FP_005fNORMAL-2346"></a><dd>This value is returned for all other values of <var>x</var>. It indicates |
| that there is nothing special about the number. |
| </dl> |
| |
| </blockquote></div> |
| |
| <p><code>fpclassify</code> is most useful if more than one property of a number |
| must be tested. There are more specific macros which only test one |
| property at a time. Generally these macros execute faster than |
| <code>fpclassify</code>, since there is special hardware support for them. |
| You should therefore use the specific macros whenever possible. |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isfinite</b> (<em>float-type</em><var> x</var>)<var><a name="index-isfinite-2347"></a></var><br> |
| <blockquote><p>This macro returns a nonzero value if <var>x</var> is finite: not plus or |
| minus infinity, and not NaN. It is equivalent to |
| |
| <pre class="smallexample"> (fpclassify (x) != FP_NAN && fpclassify (x) != FP_INFINITE) |
| </pre> |
| <p><code>isfinite</code> is implemented as a macro which accepts any |
| floating-point type. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isnormal</b> (<em>float-type</em><var> x</var>)<var><a name="index-isnormal-2348"></a></var><br> |
| <blockquote><p>This macro returns a nonzero value if <var>x</var> is finite and normalized. |
| It is equivalent to |
| |
| <pre class="smallexample"> (fpclassify (x) == FP_NORMAL) |
| </pre> |
| </blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isnan</b> (<em>float-type</em><var> x</var>)<var><a name="index-isnan-2349"></a></var><br> |
| <blockquote><p>This macro returns a nonzero value if <var>x</var> is NaN. It is equivalent |
| to |
| |
| <pre class="smallexample"> (fpclassify (x) == FP_NAN) |
| </pre> |
| </blockquote></div> |
| |
| <p>Another set of floating-point classification functions was provided by |
| BSD. The GNU C library also supports these functions; however, we |
| recommend that you use the ISO C99 macros in new code. Those are standard |
| and will be available more widely. Also, since they are macros, you do |
| not have to worry about the type of their argument. |
| |
| <!-- math.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>isinf</b> (<var>double x</var>)<var><a name="index-isinf-2350"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- BSD --> |
| — Function: int <b>isinff</b> (<var>float x</var>)<var><a name="index-isinff-2351"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- BSD --> |
| — Function: int <b>isinfl</b> (<var>long double x</var>)<var><a name="index-isinfl-2352"></a></var><br> |
| <blockquote><p>This function returns <code>-1</code> if <var>x</var> represents negative infinity, |
| <code>1</code> if <var>x</var> represents positive infinity, and <code>0</code> otherwise. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>isnan</b> (<var>double x</var>)<var><a name="index-isnan-2353"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- BSD --> |
| — Function: int <b>isnanf</b> (<var>float x</var>)<var><a name="index-isnanf-2354"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- BSD --> |
| — Function: int <b>isnanl</b> (<var>long double x</var>)<var><a name="index-isnanl-2355"></a></var><br> |
| <blockquote><p>This function returns a nonzero value if <var>x</var> is a “not a number” |
| value, and zero otherwise. |
| |
| <p><strong>NB:</strong> The <code>isnan</code> macro defined by ISO C99<!-- /@w --> overrides |
| the BSD function. This is normally not a problem, because the two |
| routines behave identically. However, if you really need to get the BSD |
| function for some reason, you can write |
| |
| <pre class="smallexample"> (isnan) (x) |
| </pre> |
| </blockquote></div> |
| |
| <!-- math.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>finite</b> (<var>double x</var>)<var><a name="index-finite-2356"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- BSD --> |
| — Function: int <b>finitef</b> (<var>float x</var>)<var><a name="index-finitef-2357"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- BSD --> |
| — Function: int <b>finitel</b> (<var>long double x</var>)<var><a name="index-finitel-2358"></a></var><br> |
| <blockquote><p>This function returns a nonzero value if <var>x</var> is finite or a “not a |
| number” value, and zero otherwise. |
| </p></blockquote></div> |
| |
| <p><strong>Portability Note:</strong> The functions listed in this section are BSD |
| extensions. |
| |
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