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+'\" t
+.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
+.\" <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH matherr 3 2024-05-02 "Linux man-pages (unreleased)"
+.SH NAME
+matherr \- SVID math library exception handling
+.SH LIBRARY
+Math library
+.RI ( libm ", " \-lm )
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.P
+.BI "[[deprecated]] int matherr(struct exception *" exc );
+.P
+.B [[deprecated]] extern _LIB_VERSION_TYPE _LIB_VERSION;
+.fi
+.SH DESCRIPTION
+.IR Note :
+the mechanism described in this page is no longer supported by glibc.
+Before glibc 2.27, it had been marked as obsolete.
+Since glibc 2.27,
+.\" glibc commit 813378e9fe17e029caf627cab76fe23eb46815fa
+the mechanism has been removed altogether.
+New applications should use the techniques described in
+.BR math_error (7)
+and
+.BR fenv (3).
+This page documents the
+.BR matherr ()
+mechanism as an aid for maintaining and porting older applications.
+.P
+The System V Interface Definition (SVID) specifies that various
+math functions should invoke a function called
+.BR matherr ()
+if a math exception is detected.
+This function is called before the math function returns;
+after
+.BR matherr ()
+returns, the system then returns to the math function,
+which in turn returns to the caller.
+.P
+To employ
+.BR matherr (),
+the programmer must define the
+.B _SVID_SOURCE
+feature test macro
+(before including
+.I any
+header files),
+and assign the value
+.B _SVID_
+to the external variable
+.BR _LIB_VERSION .
+.P
+The system provides a default version of
+.BR matherr ().
+This version does nothing, and returns zero
+(see below for the significance of this).
+The default
+.BR matherr ()
+can be overridden by a programmer-defined
+version, which will be invoked when an exception occurs.
+The function is invoked with one argument, a pointer to an
+.I exception
+structure, defined as follows:
+.P
+.in +4n
+.EX
+struct exception {
+ int type; /* Exception type */
+ char *name; /* Name of function causing exception */
+ double arg1; /* 1st argument to function */
+ double arg2; /* 2nd argument to function */
+ double retval; /* Function return value */
+}
+.EE
+.in
+.P
+The
+.I type
+field has one of the following values:
+.TP 12
+.B DOMAIN
+A domain error occurred (the function argument was outside the range
+for which the function is defined).
+The return value depends on the function;
+.I errno
+is set to
+.BR EDOM .
+.TP
+.B SING
+A pole error occurred (the function result is an infinity).
+The return value in most cases is
+.B HUGE
+(the largest single precision floating-point number),
+appropriately signed.
+In most cases,
+.I errno
+is set to
+.BR EDOM .
+.TP
+.B OVERFLOW
+An overflow occurred.
+In most cases, the value
+.B HUGE
+is returned, and
+.I errno
+is set to
+.BR ERANGE .
+.TP
+.B UNDERFLOW
+An underflow occurred.
+0.0 is returned, and
+.I errno
+is set to
+.BR ERANGE .
+.TP
+.B TLOSS
+Total loss of significance.
+0.0 is returned, and
+.I errno
+is set to
+.BR ERANGE .
+.TP
+.B PLOSS
+Partial loss of significance.
+This value is unused on glibc
+(and many other systems).
+.P
+The
+.I arg1
+and
+.I arg2
+fields are the arguments supplied to the function
+.RI ( arg2
+is undefined for functions that take only one argument).
+.P
+The
+.I retval
+field specifies the return value that the math
+function will return to its caller.
+The programmer-defined
+.BR matherr ()
+can modify this field to change the return value of the math function.
+.P
+If the
+.BR matherr ()
+function returns zero, then the system sets
+.I errno
+as described above, and may print an error message on standard error
+(see below).
+.P
+If the
+.BR matherr ()
+function returns a nonzero value, then the system does not set
+.IR errno ,
+and doesn't print an error message.
+.SS Math functions that employ matherr()
+The table below lists the functions and circumstances in which
+.BR matherr ()
+is called.
+The "Type" column indicates the value assigned to
+.I exc\->type
+when calling
+.BR matherr ().
+The "Result" column is the default return value assigned to
+.IR exc\->retval .
+.P
+The "Msg?" and "errno" columns describe the default behavior if
+.BR matherr ()
+returns zero.
+If the "Msg?" columns contains "y",
+then the system prints an error message on standard error.
+.P
+The table uses the following notations and abbreviations:
+.P
+.RS
+.TS
+l l.
+x first argument to function
+y second argument to function
+fin finite value for argument
+neg negative value for argument
+int integral value for argument
+o/f result overflowed
+u/f result underflowed
+|x| absolute value of x
+X_TLOSS is a constant defined in \fI<math.h>\fP
+.TE
+.RE
+.\" Details below from glibc 2.8's sysdeps/ieee754/k_standard.c
+.\" A subset of cases were test by experimental programs.
+.TS
+lB lB lB cB lB
+l l l c l.
+Function Type Result Msg? errno
+acos(|x|>1) DOMAIN HUGE y EDOM
+asin(|x|>1) DOMAIN HUGE y EDOM
+atan2(0,0) DOMAIN HUGE y EDOM
+acosh(x<1) DOMAIN NAN y EDOM \" retval is 0.0/0.0
+atanh(|x|>1) DOMAIN NAN y EDOM \" retval is 0.0/0.0
+atanh(|x|==1) SING (x>0.0)? y EDOM \" retval is x/0.0
+\ \ HUGE_VAL :
+\ \ \-HUGE_VAL
+cosh(fin) o/f OVERFLOW HUGE n ERANGE
+sinh(fin) o/f OVERFLOW (x>0.0) ? n ERANGE
+\ \ HUGE : \-HUGE
+sqrt(x<0) DOMAIN 0.0 y EDOM
+hypot(fin,fin) o/f OVERFLOW HUGE n ERANGE
+exp(fin) o/f OVERFLOW HUGE n ERANGE
+exp(fin) u/f UNDERFLOW 0.0 n ERANGE
+exp2(fin) o/f OVERFLOW HUGE n ERANGE
+exp2(fin) u/f UNDERFLOW 0.0 n ERANGE
+exp10(fin) o/f OVERFLOW HUGE n ERANGE
+exp10(fin) u/f UNDERFLOW 0.0 n ERANGE
+j0(|x|>X_TLOSS) TLOSS 0.0 y ERANGE
+j1(|x|>X_TLOSS) TLOSS 0.0 y ERANGE
+jn(|x|>X_TLOSS) TLOSS 0.0 y ERANGE
+y0(x>X_TLOSS) TLOSS 0.0 y ERANGE
+y1(x>X_TLOSS) TLOSS 0.0 y ERANGE
+yn(x>X_TLOSS) TLOSS 0.0 y ERANGE
+y0(0) DOMAIN \-HUGE y EDOM
+y0(x<0) DOMAIN \-HUGE y EDOM
+y1(0) DOMAIN \-HUGE y EDOM
+y1(x<0) DOMAIN \-HUGE y EDOM
+yn(n,0) DOMAIN \-HUGE y EDOM
+yn(x<0) DOMAIN \-HUGE y EDOM
+lgamma(fin) o/f OVERFLOW HUGE n ERANGE
+lgamma(\-int) or SING HUGE y EDOM
+\ \ lgamma(0)
+tgamma(fin) o/f OVERFLOW HUGE_VAL n ERANGE
+tgamma(\-int) SING NAN y EDOM
+tgamma(0) SING copysign( y ERANGE
+\ \ HUGE_VAL,x)
+log(0) SING \-HUGE y EDOM
+log(x<0) DOMAIN \-HUGE y EDOM
+log2(0) SING \-HUGE n EDOM \" different from log()
+log2(x<0) DOMAIN \-HUGE n EDOM \" different from log()
+log10(0) SING \-HUGE y EDOM
+log10(x<0) DOMAIN \-HUGE y EDOM
+pow(0.0,0.0) DOMAIN 0.0 y EDOM
+pow(x,y) o/f OVERFLOW HUGE n ERANGE
+pow(x,y) u/f UNDERFLOW 0.0 n ERANGE
+pow(NaN,0.0) DOMAIN x n EDOM
+0**neg DOMAIN 0.0 y EDOM \" +0 and -0
+neg**non-int DOMAIN 0.0 y EDOM
+scalb() o/f OVERFLOW (x>0.0) ? n ERANGE
+\ \ HUGE_VAL :
+\ \ \-HUGE_VAL
+scalb() u/f UNDERFLOW copysign( n ERANGE
+\ \ \ \ 0.0,x)
+fmod(x,0) DOMAIN x y EDOM
+remainder(x,0) DOMAIN NAN y EDOM \" retval is 0.0/0.0
+.TE
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface Attribute Value
+T{
+.na
+.nh
+.BR matherr ()
+T} Thread safety MT-Safe
+.TE
+.SH EXAMPLES
+The example program demonstrates the use of
+.BR matherr ()
+when calling
+.BR log (3).
+The program takes up to three command-line arguments.
+The first argument is the floating-point number to be given to
+.BR log (3).
+If the optional second argument is provided, then
+.B _LIB_VERSION
+is set to
+.B _SVID_
+so that
+.BR matherr ()
+is called, and the integer supplied in the
+command-line argument is used as the return value from
+.BR matherr ().
+If the optional third command-line argument is supplied,
+then it specifies an alternative return value that
+.BR matherr ()
+should assign as the return value of the math function.
+.P
+The following example run, where
+.BR log (3)
+is given an argument of 0.0, does not use
+.BR matherr ():
+.P
+.in +4n
+.EX
+.RB "$" " ./a.out 0.0"
+errno: Numerical result out of range
+x=\-inf
+.EE
+.in
+.P
+In the following run,
+.BR matherr ()
+is called, and returns 0:
+.P
+.in +4n
+.EX
+.RB "$" " ./a.out 0.0 0"
+matherr SING exception in log() function
+ args: 0.000000, 0.000000
+ retval: \-340282346638528859811704183484516925440.000000
+log: SING error
+errno: Numerical argument out of domain
+x=\-340282346638528859811704183484516925440.000000
+.EE
+.in
+.P
+The message "log: SING error" was printed by the C library.
+.P
+In the following run,
+.BR matherr ()
+is called, and returns a nonzero value:
+.P
+.in +4n
+.EX
+.RB "$" " ./a.out 0.0 1"
+matherr SING exception in log() function
+ args: 0.000000, 0.000000
+ retval: \-340282346638528859811704183484516925440.000000
+x=\-340282346638528859811704183484516925440.000000
+.EE
+.in
+.P
+In this case, the C library did not print a message, and
+.I errno
+was not set.
+.P
+In the following run,
+.BR matherr ()
+is called, changes the return value of the math function,
+and returns a nonzero value:
+.P
+.in +4n
+.EX
+.RB "$" " ./a.out 0.0 1 12345.0"
+matherr SING exception in log() function
+ args: 0.000000, 0.000000
+ retval: \-340282346638528859811704183484516925440.000000
+x=12345.000000
+.EE
+.in
+.SS Program source
+\&
+.\" SRC BEGIN (matherr.c)
+.EX
+#define _SVID_SOURCE
+#include <errno.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+\&
+static int matherr_ret = 0; /* Value that matherr()
+ should return */
+static int change_retval = 0; /* Should matherr() change
+ function\[aq]s return value? */
+static double new_retval; /* New function return value */
+\&
+int
+matherr(struct exception *exc)
+{
+ fprintf(stderr, "matherr %s exception in %s() function\en",
+ (exc\->type == DOMAIN) ? "DOMAIN" :
+ (exc\->type == OVERFLOW) ? "OVERFLOW" :
+ (exc\->type == UNDERFLOW) ? "UNDERFLOW" :
+ (exc\->type == SING) ? "SING" :
+ (exc\->type == TLOSS) ? "TLOSS" :
+ (exc\->type == PLOSS) ? "PLOSS" : "???",
+ exc\->name);
+ fprintf(stderr, " args: %f, %f\en",
+ exc\->arg1, exc\->arg2);
+ fprintf(stderr, " retval: %f\en", exc\->retval);
+\&
+ if (change_retval)
+ exc\->retval = new_retval;
+\&
+ return matherr_ret;
+}
+\&
+int
+main(int argc, char *argv[])
+{
+ double x;
+\&
+ if (argc < 2) {
+ fprintf(stderr, "Usage: %s <argval>"
+ " [<matherr\-ret> [<new\-func\-retval>]]\en", argv[0]);
+ exit(EXIT_FAILURE);
+ }
+\&
+ if (argc > 2) {
+ _LIB_VERSION = _SVID_;
+ matherr_ret = atoi(argv[2]);
+ }
+\&
+ if (argc > 3) {
+ change_retval = 1;
+ new_retval = atof(argv[3]);
+ }
+\&
+ x = log(atof(argv[1]));
+ if (errno != 0)
+ perror("errno");
+\&
+ printf("x=%f\en", x);
+ exit(EXIT_SUCCESS);
+}
+.EE
+.\" SRC END
+.SH SEE ALSO
+.BR fenv (3),
+.BR math_error (7),
+.BR standards (7)
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