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 <h3 class="section">1.1 Error Handling</h3>

 <p>There are four different versions of the math library routines: IEEE,
 POSIX, X/Open, or SVID.  The version may be selected at runtime by
 setting the global variable <code>_LIB_VERSION</code>, defined in
 <samp><span class="file">math.h</span></samp>.  It may be set to one of the following constants defined
 in <samp><span class="file">math.h</span></samp>: <code>_IEEE_</code>, <code>_POSIX_</code>, <code>_XOPEN_</code>, or
 <code>_SVID_</code>.  The <code>_LIB_VERSION</code> variable is not specific to any
 thread, and changing it will affect all threads.

    <p>The versions of the library differ only in how errors are handled.

    <p>In IEEE mode, the <code>matherr</code> function is never called, no warning
 messages are printed, and <code>errno</code> is never set.

    <p>In POSIX mode, <code>errno</code> is set correctly, but the <code>matherr</code>
 function is never called and no warning messages are printed.

    <p>In X/Open mode, <code>errno</code> is set correctly, and <code>matherr</code> is
 called, but warning message are not printed.

    <p>In SVID mode, functions which overflow return 3.40282346638528860e+38,
 the maximum single-precision floating-point value, rather than infinity.
 Also, <code>errno</code> is set correctly, <code>matherr</code> is called, and, if
 <code>matherr</code> returns 0, warning messages are printed for some errors.
 For example, by default &lsquo;<samp><span class="samp">log(-1.0)</span></samp>&rsquo; writes this message on standard
 error output:

 <pre class="example">     log: DOMAIN error
 </pre>
    <p>The library is set to X/Open mode by default.

    <p>The aforementioned error reporting is the supported Newlib libm error
 handling method.  However, the majority of the functions are written
 so as to produce the floating-point exceptions (e.g. "invalid",
 "divide-by-zero") as required by the C and POSIX standards, for
 floating-point implementations that support them.  Newlib does not provide
 the floating-point exception access routines defined in the standards
 for fenv.h, though, which is why they are considered unsupported.  It is
 mentioned in case you have separately-provided access routines so that
 you are aware that they can be caused.

 <h3 class="section">1.2 Standards Compliance And Portability</h3>

 <p>Most of the individual function descriptions describe the standards to which
 each function complies.  However, these descriptions are mostly out of date,
 having been written before C99 was released.  One of these days we'll get
 around to updating the rest of them.  (If you'd like to help, please let us
 know.)

    <p>&ldquo;C99&rdquo; refers to ISO/IEC 9899:1999, &ldquo;Programming languages&ndash;C&rdquo;.
 &ldquo;POSIX&rdquo; refers to IEEE Standard 1003.1.  POSIX&reg; is a
 registered trademark of The IEEE.

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	<h3 class="section">1.1 Error Handling</h3>

	<p>There are four different versions of the math library routines: IEEE,
	POSIX, X/Open, or SVID. The version may be selected at runtime by
	setting the global variable <code>_LIB_VERSION</code>, defined in
	<samp><span class="file">math.h</span></samp>. It may be set to one of the following constants defined
	in <samp><span class="file">math.h</span></samp>: <code>_IEEE_</code>, <code>_POSIX_</code>, <code>_XOPEN_</code>, or
	<code>_SVID_</code>. The <code>_LIB_VERSION</code> variable is not specific to any
	thread, and changing it will affect all threads.

	<p>The versions of the library differ only in how errors are handled.

	<p>In IEEE mode, the <code>matherr</code> function is never called, no warning
	messages are printed, and <code>errno</code> is never set.

	<p>In POSIX mode, <code>errno</code> is set correctly, but the <code>matherr</code>
	function is never called and no warning messages are printed.

	<p>In X/Open mode, <code>errno</code> is set correctly, and <code>matherr</code> is
	called, but warning message are not printed.

	<p>In SVID mode, functions which overflow return 3.40282346638528860e+38,
	the maximum single-precision floating-point value, rather than infinity.
	Also, <code>errno</code> is set correctly, <code>matherr</code> is called, and, if
	<code>matherr</code> returns 0, warning messages are printed for some errors.
	For example, by default ‘<samp><span class="samp">log(-1.0)</span></samp>’ writes this message on standard
	error output:

	<pre class="example"> log: DOMAIN error
	</pre>
	<p>The library is set to X/Open mode by default.

	<p>The aforementioned error reporting is the supported Newlib libm error
	handling method. However, the majority of the functions are written
	so as to produce the floating-point exceptions (e.g. "invalid",
	"divide-by-zero") as required by the C and POSIX standards, for
	floating-point implementations that support them. Newlib does not provide
	the floating-point exception access routines defined in the standards
	for fenv.h, though, which is why they are considered unsupported. It is
	mentioned in case you have separately-provided access routines so that
	you are aware that they can be caused.

	<h3 class="section">1.2 Standards Compliance And Portability</h3>

	<p>Most of the individual function descriptions describe the standards to which
	each function complies. However, these descriptions are mostly out of date,
	having been written before C99 was released. One of these days we'll get
	around to updating the rest of them. (If you'd like to help, please let us
	know.)

	<p>“C99” refers to ISO/IEC 9899:1999, “Programming languages–C”.
	“POSIX” refers to IEEE Standard 1003.1. POSIX® is a
	registered trademark of The IEEE.

	<!-- To sort the include list easily, keep the indentation right because want to -->
	<!-- skip the s_\|w_ at the start of most-but not all-of the file names. -->
	<!-- (e.g., isgreater.def does not have a leading s nor w.) Then, sort -->
	<!-- based on the column. For example: "sort -t@ -k3.17" -->
	<!-- A few hand-edits might be appropriate after a sort, although not necessary -->
	<!-- and are a nuisance as ought to be kept in sync with menu list above: -->
	<!-- atan2 after atan, exp2 after exp, log first in log list, and w_j0 to place -->
	<!-- to reflect function name of Bessel (as opposed to j; e.g. after atanh, -->
	<!-- before cbrt). -->
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