MATHERR(3)		   Linux Programmer's Manual		    MATHERR(3)



NAME
       matherr - SVID math library exception handling

SYNOPSIS
       #include <math.h>

       int matherr(struct exception *exc);

       extern _LIB_VERSION_TYPE _LIB_VERSION;

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       significand(), significandf(), significandl():
	   /* Since glibc 2.19: */ _DEFAULT_SOURCE
	       || /* Glibc versions <= 2.19: */ _SVID_SOURCE

       Link with -lm.

DESCRIPTION
       The  System  V  Interface Definition (SVID) specifies that various math
       functions should invoke a function called matherr() if a math exception
       is detected.  This function is called before the math function returns;
       after matherr() returns, the system then returns to the math  function,
       which in turn returns to the caller.

       The matherr() mechanism is supported by glibc, but is now obsolete: new
       applications should use the techniques described in  math_error(7)  and
       fenv(3).	  This	page documents the glibc matherr() mechanism as an aid
       for maintaining and porting older applications.

       To employ matherr(), the programmer must define the  _SVID_SOURCE  fea-
       ture  test  macro  (before  including any header files), and assign the
       value _SVID_ to the external variable _LIB_VERSION.

       The system provides a default version of matherr().  This version  does
       nothing,	 and  returns  zero  (see below for the significance of this).
       The default matherr() can be overridden by  a  programmer-defined  ver-
       sion,  which will be invoked when an exception occurs.  The function is
       invoked with one argument, a pointer to an exception structure, defined
       as follows:

	   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 */
	   }

       The type field has one of the following values:

       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; errno is set to EDOM.

       SING	   A pole error occurred (the function result is an infinity).
		   The return value in most cases is HUGE (the largest	single
		   precision floating-point number), appropriately signed.  In
		   most cases, errno is set to EDOM.

       OVERFLOW	   An overflow occurred.  In most cases,  the  value  HUGE  is
		   returned, and errno is set to ERANGE.

       UNDERFLOW   An  underflow  occurred.  0.0 is returned, and errno is set
		   to ERANGE.

       TLOSS	   Total loss of significance.	0.0 is returned, and errno  is
		   set to ERANGE.

       PLOSS	   Partial  loss  of  significance.   This  value is unused on
		   glibc (and many other systems).

       The arg1 and arg2 fields are the arguments  supplied  to	 the  function
       (arg2 is undefined for functions that take only one argument).

       The retval field specifies the return value that the math function will
       return to its caller.  The programmer-defined matherr() can modify this
       field to change the return value of the math function.

       If  the	matherr() function returns zero, then the system sets errno as
       described above, and may print an error message on standard error  (see
       below).

       If the matherr() function returns a nonzero value, then the system does
       not set errno, and doesn't print an error message.

   Math functions that employ matherr()
       The table below lists the functions and circumstances  in  which	 math-
       err()  is  called.   The	 "Type" column indicates the value assigned to
       exc->type when calling matherr().  The "Result" column is  the  default
       return value assigned to exc->retval.

       The  "Msg?"  and "errno" columns describe the default behavior if math-
       err() returns zero.  If the "Msg?" columns contains "y", then the  sys-
       tem prints an error message on standard error.

       The table uses the following notations and abbreviations:

	      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 <math.h>

       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
       atanh(|x|>1)	    DOMAIN	NAN		y     EDOM
       atanh(|x|==1)	    SING	(x>0.0)?	y     EDOM
					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
       log2(x<0)	    DOMAIN	-HUGE		n     EDOM
       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
       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

ATTRIBUTES
       For   an	  explanation	of   the  terms	 used  in  this	 section,  see
       attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute	  | Value   |
       +----------+---------------+---------+
       |matherr() | Thread safety | MT-Safe |
       +----------+---------------+---------+
EXAMPLE
       The example program demonstrates the  use  of  matherr()	 when  calling
       log(3).	 The  program  takes  up to three command-line arguments.  The
       first argument is the floating-point number to be given to log(3).   If
       the  optional  second argument is provided, then _LIB_VERSION is set to
       _SVID_ so that matherr() is called, and the  integer  supplied  in  the
       command-line  argument  is used as the return value from matherr().  If
       the optional third command-line argument is supplied, then it specifies
       an  alternative return value that matherr() should assign as the return
       value of the math function.

       The following example run, where log(3) is given an  argument  of  0.0,
       does not use matherr():

	   $ ./a.out 0.0
	   errno: Numerical result out of range
	   x=-inf

       In the following run, matherr() is called, and returns 0:

	   $ ./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

       The message "log: SING error" was printed by the C library.

       In the following run, matherr() is called, and returns a nonzero value:

	   $ ./a.out 0.0 1
	   matherr SING exception in log() function
		   args:   0.000000, 0.000000
		   retval: -340282346638528859811704183484516925440.000000
	   x=-340282346638528859811704183484516925440.000000

       In  this case, the C library did not print a message, and errno was not
       set.

       In the following run, matherr() is called, changes the return value  of
       the math function, and returns a nonzero value:

	   $ ./a.out 0.0 1 12345.0
	   matherr SING exception in log() function
		   args:   0.000000, 0.000000
		   retval: -340282346638528859811704183484516925440.000000
	   x=12345.000000

   Program source

       #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's return value? */
       static double new_retval;       /* New function return value */

       int
       matherr(struct exception *exc)
       {
	   fprintf(stderr, "matherr %s exception in %s() function\n",
		  (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\n",
		   exc->arg1, exc->arg2);
	   fprintf(stderr, "	    retval: %f\n", 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>]]\n", 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\n", x);
	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       fenv(3), math_error(7), standards(7)

COLOPHON
       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-03-15			    MATHERR(3)