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>Math library compatibility modes</TITLE
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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
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