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<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >Math library compatibility modes</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="C and math library overview" HREF="c-and-math-library-overview.html"><LINK REL="PREVIOUS" TITLE="C and math library overview" HREF="c-and-math-library-overview.html"><LINK REL="NEXT" TITLE="Some implementation details" HREF="libc-implementation-details.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="c-and-math-library-overview.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 13. C and math library overview</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="libc-implementation-details.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="MATH-LIBRARY-COMPATIBILITY-MODES">Math library compatibility modes</H1 ><P >This math library is capable of being operated in several different compatibility modes. These options deal solely with how errors are handled. </P ><P >There are 4 compatibility modes: ANSI/POSIX 1003.1; IEEE-754; X/Open Portability Guide issue 3 (XPG3); and System V Interface Definition Edition 3. </P ><P >In IEEE mode, the <TT CLASS="FUNCTION" >matherr()</TT > function (see below) is never called, no warning messages are printed on the stderr output stream, and errno is never set. </P ><P >In ANSI/POSIX mode, errno is set correctly, but <TT CLASS="FUNCTION" >matherr()</TT > is never called and no warning messages are printed on the stderr output stream. </P ><P >In X/Open mode, errno is set correctly, <TT CLASS="FUNCTION" >matherr()</TT > is called, but no warning messages are printed on the stderr output stream. </P ><P >In SVID mode, functions which overflow return a value HUGE (defined in <TT CLASS="FILENAME" >math.h</TT >), which is the maximum single precision floating point value (as opposed to HUGE_VAL which is meant to stand for infinity). errno is set correctly and <TT CLASS="FUNCTION" >matherr()</TT > is called. If <TT CLASS="FUNCTION" >matherr()</TT > returns 0, warning messages are printed on the stderr output stream for some errors. </P ><P >The mode can be compiled-in as IEEE-only, or any one of the above methods settable at run-time. </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B >This math library assumes that the hardware (or software floating point emulation) supports IEEE-754 style arithmetic, 32-bit 2's complement integer arithmetic, doubles are in 64-bit IEEE-754 format.</P ></BLOCKQUOTE ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN10153">matherr()</H2 ><P >As mentioned above, in X/Open or SVID modes, the user can supply a function <TT CLASS="FUNCTION" >matherr()</TT > of the form:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >int <TT CLASS="FUNCTION" >matherr</TT >( struct exception *e )</PRE ></TD ></TR ></TABLE ><P >where struct exception is defined as:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >struct exception { int type; char *name; double arg1, arg2, retval; }; </PRE ></TD ></TR ></TABLE ><P >type is the exception type and is one of:</P ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT >DOMAIN</DT ><DD ><P >argument domain exception</P ></DD ><DT >SING</DT ><DD ><P >argument singularity</P ></DD ><DT >OVERFLOW</DT ><DD ><P >overflow range exception</P ></DD ><DT >UNDERFLOW</DT ><DD ><P >underflow range exception</P ></DD ><DT >TLOSS</DT ><DD ><P >total loss of significance</P ></DD ><DT >PLOSS</DT ><DD ><P >partial loss of significance</P ></DD ></DL ></DIV ><P ><TT CLASS="PARAMETER" ><I >name</I ></TT > is a string containing the name of the function</P ><P ><TT CLASS="PARAMETER" ><I >arg1</I ></TT > and <TT CLASS="PARAMETER" ><I >arg2</I ></TT > are the arguments passed to the function</P ><P ><TT CLASS="PARAMETER" ><I >retval</I ></TT > is the default value that will be returned by the function, and can be changed by <TT CLASS="FUNCTION" >matherr()</TT ></P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B >matherr must have “C” linkage, not “C++” linkage.</P ></BLOCKQUOTE ></DIV ><P >If matherr returns zero, or the user doesn't supply their own matherr, then the following <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >usually</I ></SPAN > happens in SVID mode:</P ><DIV CLASS="TABLE" ><A NAME="AEN10199"><P ><B >Table 13-1. Behavior of math exception handling</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><THEAD ><TR ><TH ALIGN="LEFT" VALIGN="TOP" >Type</TH ><TH ALIGN="LEFT" VALIGN="TOP" >Behavior</TH ></TR ></THEAD ><TBODY ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >DOMAIN</TD ><TD ALIGN="LEFT" VALIGN="TOP" >0.0 returned, errno=EDOM, and a message printed on stderr</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >SING</TD ><TD ALIGN="LEFT" VALIGN="TOP" >HUGE of appropriate sign is returned, errno=EDOM, and a message is printed on stderr</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >OVERFLOW</TD ><TD ALIGN="LEFT" VALIGN="TOP" >HUGE of appropriate sign is returned, and errno=ERANGE</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >UNDERFLOW</TD ><TD ALIGN="LEFT" VALIGN="TOP" >0.0 is returned and errno=ERANGE</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >TLOSS</TD ><TD ALIGN="LEFT" VALIGN="TOP" >0.0 is returned, errno=ERANGE, and a message is printed on stderr</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >PLOSS</TD ><TD ALIGN="LEFT" VALIGN="TOP" >The current implementation doesn't return this type</TD ></TR ></TBODY ></TABLE ></DIV ><P >X/Open mode is similar except that the message is not printed on stderr and HUGE_VAL is used in place of HUGE</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN10226">Thread-safety and re-entrancy</H2 ><P >With the appropriate configuration options set below, the math library is fully thread-safe if:</P ><P ></P ><UL ><LI ><P >Depending on the compatibility mode, the setting of the errno variable from the C library is thread-safe</P ></LI ><LI ><P >Depending on the compatibility mode, sending error messages to the stderr output stream using the C library <TT CLASS="FUNCTION" >fputs()</TT > function is thread-safe </P ></LI ><LI ><P >Depending on the compatibility mode, the user-supplied <TT CLASS="FUNCTION" >matherr()</TT > function and anything it depends on are thread-safe </P ></LI ></UL ><P >In addition, with the exception of the <TT CLASS="FUNCTION" >gamma*()</TT > and <TT CLASS="FUNCTION" >lgamma*()</TT > functions, the math library is reentrant (and thus safe to use from interrupt handlers) if the Math library is always in IEEE mode.</P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="c-and-math-library-overview.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="libc-implementation-details.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >C and math library overview</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c-and-math-library-overview.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Some implementation details</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
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