unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (Debian-5.0)
Page:
Section:
Apropos / Subsearch:
optional field

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



NAME
       matherr - SVID math library exception handling

SYNOPSIS
       #define _SVID_SOURCE
       #include <&lt;math.h>&gt;

       int matherr(struct exception *exc);

       extern _LIB_VERSION_TYPE _LIB_VERSION;

       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, 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 non-zero 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-&gt;type when calling matherr().  The "Result" column is  the  default
       return value assigned to exc-&gt;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 &lt;math.h&gt;

       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
       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  OVER-
       FLOW  HUGE n    ERANGE     exp(fin)    o/f   OVERFLOW  HUGE n    ERANGE
       exp(fin)    u/f  UNDERFLOW 0.0  n    ERANGE    exp2(fin)     o/f  OVER-
       FLOW  HUGE n    ERANGE     exp2(fin)    u/f  UNDERFLOW 0.0  n    ERANGE
       exp10(fin)  o/f     OVERFLOW  HUGE n    ERANGE  exp10(fin)   u/f UNDER-
       FLOW 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     OVER-
       FLOW  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   OVER-
       FLOW  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                              remain-
       der(x,0) DOMAIN    NAN  y    EDOM

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 non-zero
       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 non-zero 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

   Example code
       #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 3.05 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-07-21                        MATHERR(3)