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| <h3 class="section">1.31 <code>fpclassify</code>, <code>isfinite</code>, <code>isinf</code>, <code>isnan</code>, and <code>isnormal</code>–floating-point classification macros; <code>finite</code>, <code>finitef</code>, <code>isinf</code>, <code>isinff</code>, <code>isnan</code>, <code>isnanf</code>–test for exceptional numbers</h3> |
| |
| <p><a name="index-fpclassify-85"></a><a name="index-isfinite-86"></a><a name="index-isinf-87"></a><a name="index-isnan-88"></a><a name="index-isnormal-89"></a><a name="index-isnan-90"></a><a name="index-isinf-91"></a><a name="index-finite-92"></a><a name="index-isnanf-93"></a><a name="index-isinff-94"></a><a name="index-finitef-95"></a><strong>Synopsis</strong> |
| <pre class="example"> [C99 standard macros:] |
| #include <math.h> |
| int fpclassify(real-floating <var>x</var>); |
| int isfinite(real-floating <var>x</var>); |
| int isinf(real-floating <var>x</var>); |
| int isnan(real-floating <var>x</var>); |
| int isnormal(real-floating <var>x</var>); |
| |
| [Archaic SUSv2 functions:] |
| #include <ieeefp.h> |
| int isnan(double <var>arg</var>); |
| int isinf(double <var>arg</var>); |
| int finite(double <var>arg</var>); |
| int isnanf(float <var>arg</var>); |
| int isinff(float <var>arg</var>); |
| int finitef(float <var>arg</var>); |
| |
| </pre> |
| <p><strong>Description</strong><br> |
| <code>fpclassify</code>, <code>isfinite</code>, <code>isinf</code>, <code>isnan</code>, and <code>isnormal</code> are macros |
| defined for use in classifying floating-point numbers. This is a help because |
| of special "values" like NaN and infinities. In the synopses shown, |
| "real-floating" indicates that the argument is an expression of real floating |
| type. These function-like macros are C99 and POSIX-compliant, and should be |
| used instead of the now-archaic SUSv2 functions. |
| |
| <p>The <code>fpclassify</code> macro classifies its argument value as NaN, infinite, normal, |
| subnormal, zero, or into another implementation-defined category. First, an |
| argument represented in a format wider than its semantic type is converted to |
| its semantic type. Then classification is based on the type of the argument. |
| The <code>fpclassify</code> macro returns the value of the number classification macro |
| appropriate to the value of its argument: |
| |
| <dl> |
| <dt><code>FP_INFINITE</code><dd><var>x</var> is either plus or minus infinity; |
| <br><dt><code>FP_NAN</code><dd><var>x</var> is "Not A Number" (plus or minus); |
| <br><dt><code>FP_NORMAL</code><dd><var>x</var> is a "normal" number (i.e. is none of the other special forms); |
| <br><dt><code>FP_SUBNORMAL</code><dd><var>x</var> is too small be stored as a regular normalized number (i.e. loss of precision is likely); or |
| <br><dt><code>FP_ZERO</code><dd><var>x</var> is 0 (either plus or minus). |
| </dl> |
| |
| <p>The "<code>is</code>" set of macros provide a useful set of shorthand ways for |
| classifying floating-point numbers, providing the following equivalent |
| relations: |
| |
| <dl> |
| <dt><code>isfinite(</code><var>x</var><code>)</code><dd>returns non-zero if <var>x</var> is finite. (It is equivalent to |
| (<code>fpclassify</code>(<var>x</var>) != FP_INFINITE && <code>fpclassify</code>(<var>x</var>) != FP_NAN).) |
| |
| <br><dt><code>isinf(</code><var>x</var><code>)</code><dd>returns non-zero if <var>x</var> is infinite. (It is equivalent to |
| (<code>fpclassify</code>(<var>x</var>) == FP_INFINITE).) |
| |
| <br><dt><code>isnan(</code><var>x</var><code>)</code><dd>returns non-zero if <var>x</var> is NaN. (It is equivalent to |
| (<code>fpclassify</code>(<var>x</var>) == FP_NAN).) |
| |
| <br><dt><code>isnormal(</code><var>x</var><code>)</code><dd>returns non-zero if <var>x</var> is normal. (It is equivalent to |
| (<code>fpclassify</code>(<var>x</var>) == FP_NORMAL).) |
| </dl> |
| |
| <p>The archaic SUSv2 functions provide information on the floating-point |
| argument supplied. |
| |
| <p>There are five major number formats ("exponent" referring to the |
| biased exponent in the binary-encoded number): |
| <dl> |
| <dt><code>zero</code><dd>A number which contains all zero bits, excluding the sign bit. |
| <br><dt><code>subnormal</code><dd>A number with a zero exponent but a nonzero fraction. |
| <br><dt><code>normal</code><dd>A number with an exponent and a fraction. |
| <br><dt><code>infinity</code><dd>A number with an all 1's exponent and a zero fraction. |
| <br><dt><code>NAN</code><dd>A number with an all 1's exponent and a nonzero fraction. |
| |
| </dl> |
| |
| <p><code>isnan</code> returns 1 if the argument is a nan. <code>isinf</code> |
| returns 1 if the argument is infinity. <code>finite</code> returns 1 if the |
| argument is zero, subnormal or normal. |
| The <code>isnanf</code>, <code>isinff</code> and <code>finitef</code> functions perform the same |
| operations as their <code>isnan</code>, <code>isinf</code> and <code>finite</code> |
| counterparts, but on single-precision floating-point numbers. |
| |
| <p>It should be noted that the C99 standard dictates that <code>isnan</code> |
| and <code>isinf</code> are macros that operate on multiple types of |
| floating-point. The SUSv2 standard declares <code>isnan</code> as |
| a function taking double. Newlib has decided to declare |
| them both as macros in math.h and as functions in ieeefp.h to |
| maintain backward compatibility. |
| |
| <p><br> |
| <strong>Returns</strong><br> |
| <!-- Formatting note: "$@" forces a new line --> |
| The fpclassify macro returns the value corresponding to the appropriate FP_ macro.<br> |
| The isfinite macro returns nonzero if <var>x</var> is finite, else 0.<br> |
| The isinf macro returns nonzero if <var>x</var> is infinite, else 0.<br> |
| The isnan macro returns nonzero if <var>x</var> is an NaN, else 0.<br> |
| The isnormal macro returns nonzero if <var>x</var> has a normal value, else 0. |
| |
| <p><br> |
| <strong>Portability</strong><br> |
| math.h macros are C99, POSIX. |
| |
| <p>ieeefp.h funtions are outdated and should be avoided. |
| |
| <p><br> |
| |
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