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| <h4 class="subsection">20.8.1 Absolute Value</h4> |
| |
| <p><a name="index-absolute-value-functions-2404"></a> |
| These functions are provided for obtaining the <dfn>absolute value</dfn> (or |
| <dfn>magnitude</dfn>) of a number. The absolute value of a real number |
| <var>x</var> is <var>x</var> if <var>x</var> is positive, −<var>x</var> if <var>x</var> is |
| negative. For a complex number <var>z</var>, whose real part is <var>x</var> and |
| whose imaginary part is <var>y</var>, the absolute value is <code>sqrt (</code><var>x</var><code>*</code><var>x</var><code> + </code><var>y</var><code>*</code><var>y</var><code>)</code><!-- /@w -->. |
| |
| <p><a name="index-math_002eh-2405"></a><a name="index-stdlib_002eh-2406"></a>Prototypes for <code>abs</code>, <code>labs</code> and <code>llabs</code> are in <samp><span class="file">stdlib.h</span></samp>; |
| <code>imaxabs</code> is declared in <samp><span class="file">inttypes.h</span></samp>; |
| <code>fabs</code>, <code>fabsf</code> and <code>fabsl</code> are declared in <samp><span class="file">math.h</span></samp>. |
| <code>cabs</code>, <code>cabsf</code> and <code>cabsl</code> are declared in <samp><span class="file">complex.h</span></samp>. |
| |
| <!-- stdlib.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: int <b>abs</b> (<var>int number</var>)<var><a name="index-abs-2407"></a></var><br> |
| <blockquote><!-- stdlib.h --> |
| <!-- ISO --> |
| — Function: long int <b>labs</b> (<var>long int number</var>)<var><a name="index-labs-2408"></a></var><br> |
| <blockquote><!-- stdlib.h --> |
| <!-- ISO --> |
| — Function: long long int <b>llabs</b> (<var>long long int number</var>)<var><a name="index-llabs-2409"></a></var><br> |
| <blockquote><!-- inttypes.h --> |
| <!-- ISO --> |
| — Function: intmax_t <b>imaxabs</b> (<var>intmax_t number</var>)<var><a name="index-imaxabs-2410"></a></var><br> |
| <blockquote><p>These functions return the absolute value of <var>number</var>. |
| |
| <p>Most computers use a two's complement integer representation, in which |
| the absolute value of <code>INT_MIN</code> (the smallest possible <code>int</code>) |
| cannot be represented; thus, <code>abs (INT_MIN)</code><!-- /@w --> is not defined. |
| |
| <p><code>llabs</code> and <code>imaxdiv</code> are new to ISO C99<!-- /@w -->. |
| |
| <p>See <a href="Integers.html#Integers">Integers</a> for a description of the <code>intmax_t</code> type. |
| |
| </blockquote></div> |
| |
| <!-- math.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>fabs</b> (<var>double number</var>)<var><a name="index-fabs-2411"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: float <b>fabsf</b> (<var>float number</var>)<var><a name="index-fabsf-2412"></a></var><br> |
| <blockquote><!-- math.h --> |
| <!-- ISO --> |
| — Function: long double <b>fabsl</b> (<var>long double number</var>)<var><a name="index-fabsl-2413"></a></var><br> |
| <blockquote><p>This function returns the absolute value of the floating-point number |
| <var>number</var>. |
| </p></blockquote></div> |
| |
| <!-- complex.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: double <b>cabs</b> (<var>complex double z</var>)<var><a name="index-cabs-2414"></a></var><br> |
| <blockquote><!-- complex.h --> |
| <!-- ISO --> |
| — Function: float <b>cabsf</b> (<var>complex float z</var>)<var><a name="index-cabsf-2415"></a></var><br> |
| <blockquote><!-- complex.h --> |
| <!-- ISO --> |
| — Function: long double <b>cabsl</b> (<var>complex long double z</var>)<var><a name="index-cabsl-2416"></a></var><br> |
| <blockquote><p>These functions return the absolute value of the complex number <var>z</var> |
| (see <a href="Complex-Numbers.html#Complex-Numbers">Complex Numbers</a>). The absolute value of a complex number is: |
| |
| <pre class="smallexample"> sqrt (creal (<var>z</var>) * creal (<var>z</var>) + cimag (<var>z</var>) * cimag (<var>z</var>)) |
| </pre> |
| <p>This function should always be used instead of the direct formula |
| because it takes special care to avoid losing precision. It may also |
| take advantage of hardware support for this operation. See <code>hypot</code> |
| in <a href="Exponents-and-Logarithms.html#Exponents-and-Logarithms">Exponents and Logarithms</a>. |
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