mirror of https://github.com/mkerrisk/man-pages
A description of the SVID-specified mechanism for reporting math exceptions.
See http://thread.gmane.org/gmane.linux.man/266.
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'\" t
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.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH MATHERR 3 2008-07-21 "Linux" "Linux Programmer's Manual"
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.SH NAME
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matherr \- SVID math library exception handling
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.SH SYNOPSIS
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.nf
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.B #define _SVID_SOURCE
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.B #include <math.h>
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.BI "int matherr(struct exception *" exc );
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.B extern _LIB_VERSION_TYPE _LIB_VERSION;
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.fi
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.sp
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Link with \fI\-lm\fP.
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.SH DESCRIPTION
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The System V Interface Definition (SVID) specifies that various
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math functions should invoke a function called
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.BR matherr ()
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if a math exception is detected.
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This function is called before the math function returns;
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after
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.BR matherr ()
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returns, the system then returns to the math function,
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which in turn returns to the caller.
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The
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.BR matherr ()
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mechanism is supported by glibc, but is now obsolete:
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new applications should use the techniques described in
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.BR math_error (7)
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and
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.BR fenv (3).
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This page documents the glibc
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.BR matherr ()
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mechanism as an aid for maintaining and porting older applications.
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To employ
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.BR matherr (),
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the programmer must define the
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.B _SVID_SOURCE
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feature test macro, and assign the value
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.B _SVID_
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to the external variable
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.BR _LIB_VERSION .
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The system provides a default version of
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.BR matherr ().
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This version does nothing, and returns zero
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(see below for the significance of this).
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The default
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.BR matherr ()
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can be overridden by a programmer-defined
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version, which will be invoked when an exception occurs.
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The function is invoked with one argument, a pointer to an
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.I exception
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structure, defined as follows:
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.in +4n
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.nf
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struct exception {
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int type; /* Exception type */
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char *name; /* Name of function causing exception */
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double arg1; /* 1st argument to function */
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double arg2; /* 2nd argument to function */
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double retval; /* Function return value */
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}
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.fi
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.in
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.PP
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The
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.I type
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field has one of the following values:
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.TP 12
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.B DOMAIN
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A domain error occurred (the function argument was outside the range
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for which the function is defined).
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The return value depends on the function;
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.I errno
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is set to
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.BR EDOM .
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.TP
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.B SING
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A pole error occurred (the function result is an infinity).
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The return value in most cases is
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.B HUGE
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(the largest single precision floating-point number),
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appropriately signed.
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In most cases,
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.I errno
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is set to
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.BR EDOM .
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.TP
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.B OVERFLOW
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An overflow occurred.
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In most cases, the value
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.B HUGE
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is returned, and
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.I errno
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is set to
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.BR ERANGE .
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.TP
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.B UNDERFLOW
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An underflow occurred.
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0.0 is returned, and
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.I errno
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is set to
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.BR ERANGE .
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.TP
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.B TLOSS
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Total loss of significance.
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0.0 is returned, and
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.I errno
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is set to
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.BR ERANGE .
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.TP
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.B PLOSS
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Partial loss of significance.
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This value is unused on glibc
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(and many other systems).
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.PP
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The
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.I arg1
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and
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.I arg2
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fields are the arguments supplied to the function
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.RI ( arg2
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is undefined for functions that take only one argument).
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The
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.I retval
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field specifies the return value that the math
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function will return to its caller.
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The programmer-defined
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.BR matherr ()
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can modify this field to change the return value of the math function.
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If the
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.BR matherr ()
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function returns zero, then the system sets
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.I errno
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as described above, and may print an error message on standard error
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(see below).
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If the
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.BR matherr ()
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function returns a non-zero value, then the system does not set
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.IR errno ,
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and doesn't print an error message.
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.SS Math functions that employ matherr()
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The table below lists the functions and circumstances in which
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.BR matherr ()
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is called.
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The "Type" column indicates the value assigned to
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.I exc\->type
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when calling
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.BR matherr ().
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The "Result" column is the default return value assigned to
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.IR exc\->retval .
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The "Msg?" and "errno" columns describe the default behavior if
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.BR matherr ()
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returns zero.
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If the "Msg?" columns contains "y",
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then the system prints an error message on standard error.
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The table uses the following notations and abbreviations:
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.RS
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.nf
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x first argument to function
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y second argument to function
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fin finite value for argument
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neg negative value for argument
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int integral value for argument
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o/f result overflowed
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u/f result underflowed
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|x| absolute value of x
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X_TLOSS is a constant defined in \fI<math.h>\fP
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.fi
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.RE
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.\" Details below from glibc 2.8's sysdeps/ieee754/k_standard.c
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.\" A subset of cases were test by experimental programs.
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.TS
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lB lB lB cB lB
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l l l c l.
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Function Type Result Msg? errno
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acos(|x|>1) DOMAIN HUGE y EDOM
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asin(|x|>1) DOMAIN HUGE y EDOM
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atan2(0,0) DOMAIN HUGE y EDOM
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acosh(x<1) DOMAIN NAN y EDOM \" retval is 0.0/0.0
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atanh(|x|>1) DOMAIN NAN y EDOM \" retval is 0.0/0.0
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atanh(|x|==1) SING (x>0.0)? y EDOM \" retval is x/0.0
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\ \ HUGE_VAL :
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\ \ \-HUGE_VAL
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cosh(fin) o/f OVERFLOW HUGE n ERANGE
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sinh(fin) o/f OVERFLOW (x>0.0) ? n ERANGE
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\ \ HUGE : \-HUGE
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sqrt(x<0) DOMAIN 0.0 y EDOM
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hypot(fin,fin) o/f OVERFLOW HUGE n ERANGE
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exp(fin) o/f OVERFLOW HUGE n ERANGE
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exp(fin) u/f UNDERFLOW 0.0 n ERANGE
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exp2(fin) o/f OVERFLOW HUGE n ERANGE
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exp2(fin) u/f UNDERFLOW 0.0 n ERANGE
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exp10(fin) o/f OVERFLOW HUGE n ERANGE
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exp10(fin) u/f UNDERFLOW 0.0 n ERANGE
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j0(|x|>X_TLOSS) TLOSS 0.0 y ERANGE
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j1(|x|>X_TLOSS) TLOSS 0.0 y ERANGE
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jn(|x|>X_TLOSS) TLOSS 0.0 y ERANGE
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y0(x>X_TLOSS) TLOSS 0.0 y ERANGE
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y1(x>X_TLOSS) TLOSS 0.0 y ERANGE
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yn(x>X_TLOSS) TLOSS 0.0 y ERANGE
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y0(0) DOMAIN \-HUGE y EDOM
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y0(x<0) DOMAIN \-HUGE y EDOM
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y1(0) DOMAIN \-HUGE y EDOM
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y1(x<0) DOMAIN \-HUGE y EDOM
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yn(n,0) DOMAIN \-HUGE y EDOM
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yn(x<0) DOMAIN \-HUGE y EDOM
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lgamma(fin) o/f OVERFLOW HUGE n ERANGE
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lgamma(\-int) or SING HUGE y EDOM
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\ \ lgamma(0)
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tgamma(fin) o/f OVERFLOW HUGE_VAL n ERANGE
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tgamma(\-int) SING NAN y EDOM
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tgamma(0) SING copysign( y ERANGE
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\ \ HUGE_VAL,x)
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log(0) SING \-HUGE y EDOM
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log(x<0) DOMAIN \-HUGE y EDOM
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log2(0) SING \-HUGE n EDOM \" different from log()
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log2(x<0) DOMAIN -HUGE n EDOM \" different from log()
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log10(0) SING \-HUGE y EDOM
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log10(x<0) DOMAIN \-HUGE y EDOM
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pow(0.0,0.0) DOMAIN 0.0 y EDOM
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pow(x,y) o/f OVERFLOW HUGE n ERANGE
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pow(x,y) u/f UNDERFLOW 0.0 n ERANGE
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pow(NaN,0.0) DOMAIN x n EDOM
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0**neg DOMAIN 0.0 y EDOM \" +0 and -0
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neg**non-int DOMAIN 0.0 y EDOM
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scalb() o/f OVERFLOW (x>0.0) ? n ERANGE
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\ \ HUGE_VAL :
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\ \ \-HUGE_VAL
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scalb() u/f UNDERFLOW copysign( n ERANGE
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\ \ \ \ 0.0,x)
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fmod(x,0) DOMAIN x y EDOM
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remainder(x,0) DOMAIN NAN y EDOM \" retval is 0.0/0.0
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.TE
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.SH EXAMPLE
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The example program demonstrates the use of
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.BR matherr ()
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when calling
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.BR log (3).
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The program takes up to three command-line arguments.
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The first argument is the floating-point number to be given to
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.BR log (3).
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If the optional second argument is provided, then
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.B _LIB_VERSION
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is set to
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.B _SVID_
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so that
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.BR matherr ()
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is called, and the integer supplied in the
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command-line argument is used as the return value from
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.BR matherr ().
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If the optional third command-line argument is supplied,
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then it specifies an alternative return value that
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.BR matherr ()
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should assign as the return value of the math function.
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The following example run, where
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.BR log (3)
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is given an argument of 0.0, does not use
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.BR matherr() :
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.in +4n
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.nf
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$ ./a.out 0.0
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errno: Numerical result out of range
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x=-inf
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.fi
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.in
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In the following run,
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.BR matherr ()
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is called, and returns 0:
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.in +4n
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.nf
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$ ./a.out 0.0 0
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matherr SING exception in log() function
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args: 0.000000, 0.000000
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retval: -340282346638528859811704183484516925440.000000
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log: SING error
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errno: Numerical argument out of domain
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x=-340282346638528859811704183484516925440.000000
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.fi
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.in
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The message "log: SING error" was printed by the C library.
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In the following run,
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.BR matherr ()
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is called, and returns a non-zero value:
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.in +4n
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.nf
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$ ./a.out 0.0 1
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matherr SING exception in log() function
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args: 0.000000, 0.000000
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retval: -340282346638528859811704183484516925440.000000
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x=-340282346638528859811704183484516925440.000000
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.fi
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.in
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In this case, the C library did not print a message, and
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.I errno
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was not set.
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In the following run,
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.BR matherr ()
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is called, changes the return value of the math function,
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and returns a non-zero value:
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.in +4n
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.nf
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$ ./a.out 0.0 1 12345.0
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matherr SING exception in log() function
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args: 0.000000, 0.000000
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retval: -340282346638528859811704183484516925440.000000
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x=12345.000000
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.fi
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.in
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.SS Example code
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.nf
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#define _SVID_SOURCE
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#include <errno.h>
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#include <math.h>
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#include <stdio.h>
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#include <stdlib.h>
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static int matherr_ret = 0; /* Value that matherr()
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should return */
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static int change_retval = 0; /* Should matherr() change
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function\(aqs return value? */
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static double new_retval; /* New function return value */
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int
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matherr(struct exception *exc)
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{
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fprintf(stderr, "matherr %s exception in %s() function\\n",
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(exc\->type == DOMAIN) ? "DOMAIN" :
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(exc\->type == OVERFLOW) ? "OVERFLOW" :
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(exc\->type == UNDERFLOW) ? "UNDERFLOW" :
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(exc\->type == SING) ? "SING" :
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(exc\->type == TLOSS) ? "TLOSS" :
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(exc\->type == PLOSS) ? "PLOSS" : "???",
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exc\->name);
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fprintf(stderr, " args: %f, %f\\n",
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exc\->arg1, exc->arg2);
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fprintf(stderr, " retval: %f\\n", exc\->retval);
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if (change_retval)
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exc\->retval = new_retval;
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return matherr_ret;
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}
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int
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main(int argc, char *argv[])
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{
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double x;
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if (argc < 2) {
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fprintf(stderr, "Usage: %s <argval>"
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" [<matherr\-ret> [<new\-func-retval>]]\\n", argv[0]);
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exit(EXIT_FAILURE);
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}
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if (argc > 2) {
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_LIB_VERSION = _SVID_;
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matherr_ret = atoi(argv[2]);
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}
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if (argc > 3) {
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change_retval = 1;
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new_retval = atof(argv[3]);
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}
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x = log(atof(argv[1]));
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if (errno != 0)
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perror("errno");
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printf("x=%f\\n", x);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH SEE ALSO
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.\" FIXME(mtk) Add SEE ALSO in fenv(3)
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.BR fenv (3),
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.BR math_error (7),
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.BR standards (7)
|
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