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| <h4 class="subsection">20.8.6 Floating-Point Comparison Functions</h4> |
| |
| <p><a name="index-unordered-comparison-2496"></a> |
| The standard C comparison operators provoke exceptions when one or other |
| of the operands is NaN. For example, |
| |
| <pre class="smallexample"> int v = a < 1.0; |
| </pre> |
| <p class="noindent">will raise an exception if <var>a</var> is NaN. (This does <em>not</em> |
| happen with <code>==</code> and <code>!=</code>; those merely return false and true, |
| respectively, when NaN is examined.) Frequently this exception is |
| undesirable. ISO C99<!-- /@w --> therefore defines comparison functions that |
| do not raise exceptions when NaN is examined. All of the functions are |
| implemented as macros which allow their arguments to be of any |
| floating-point type. The macros are guaranteed to evaluate their |
| arguments only once. |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isgreater</b> (<em>real-floating</em><var> x, </var><em>real-floating</em><var> y</var>)<var><a name="index-isgreater-2497"></a></var><br> |
| <blockquote><p>This macro determines whether the argument <var>x</var> is greater than |
| <var>y</var>. It is equivalent to <code>(</code><var>x</var><code>) > (</code><var>y</var><code>)</code>, but no |
| exception is raised if <var>x</var> or <var>y</var> are NaN. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isgreaterequal</b> (<em>real-floating</em><var> x, </var><em>real-floating</em><var> y</var>)<var><a name="index-isgreaterequal-2498"></a></var><br> |
| <blockquote><p>This macro determines whether the argument <var>x</var> is greater than or |
| equal to <var>y</var>. It is equivalent to <code>(</code><var>x</var><code>) >= (</code><var>y</var><code>)</code>, but no |
| exception is raised if <var>x</var> or <var>y</var> are NaN. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isless</b> (<em>real-floating</em><var> x, </var><em>real-floating</em><var> y</var>)<var><a name="index-isless-2499"></a></var><br> |
| <blockquote><p>This macro determines whether the argument <var>x</var> is less than <var>y</var>. |
| It is equivalent to <code>(</code><var>x</var><code>) < (</code><var>y</var><code>)</code>, but no exception is |
| raised if <var>x</var> or <var>y</var> are NaN. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>islessequal</b> (<em>real-floating</em><var> x, </var><em>real-floating</em><var> y</var>)<var><a name="index-islessequal-2500"></a></var><br> |
| <blockquote><p>This macro determines whether the argument <var>x</var> is less than or equal |
| to <var>y</var>. It is equivalent to <code>(</code><var>x</var><code>) <= (</code><var>y</var><code>)</code>, but no |
| exception is raised if <var>x</var> or <var>y</var> are NaN. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>islessgreater</b> (<em>real-floating</em><var> x, </var><em>real-floating</em><var> y</var>)<var><a name="index-islessgreater-2501"></a></var><br> |
| <blockquote><p>This macro determines whether the argument <var>x</var> is less or greater |
| than <var>y</var>. It is equivalent to <code>(</code><var>x</var><code>) < (</code><var>y</var><code>) || |
| (</code><var>x</var><code>) > (</code><var>y</var><code>)</code> (although it only evaluates <var>x</var> and <var>y</var> |
| once), but no exception is raised if <var>x</var> or <var>y</var> are NaN. |
| |
| <p>This macro is not equivalent to <var>x</var><code> != </code><var>y</var>, because that |
| expression is true if <var>x</var> or <var>y</var> are NaN. |
| </p></blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>isunordered</b> (<em>real-floating</em><var> x, </var><em>real-floating</em><var> y</var>)<var><a name="index-isunordered-2502"></a></var><br> |
| <blockquote><p>This macro determines whether its arguments are unordered. In other |
| words, it is true if <var>x</var> or <var>y</var> are NaN, and false otherwise. |
| </p></blockquote></div> |
| |
| <p>Not all machines provide hardware support for these operations. On |
| machines that don't, the macros can be very slow. Therefore, you should |
| not use these functions when NaN is not a concern. |
| |
| <p><strong>NB:</strong> There are no macros <code>isequal</code> or <code>isunequal</code>. |
| They are unnecessary, because the <code>==</code> and <code>!=</code> operators do |
| <em>not</em> throw an exception if one or both of the operands are NaN. |
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