NAME | SYNOPSIS | DESCRIPTION | ATTRIBUTES | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       matherr - SVID math library exception handling

SYNOPSIS         top

       #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         top

       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
       feature 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 version, 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
       matherr() 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
       matherr() returns zero.  If the "Msg?" columns contains "y", then the
       system 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         top

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

       ┌──────────┬───────────────┬─────────┐
       │Interface Attribute     Value   │
       ├──────────┼───────────────┼─────────┤
       │matherr() │ Thread safety │ MT-Safe │
       └──────────┴───────────────┴─────────┘

EXAMPLE         top

       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         top

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

COLOPHON         top

       This page is part of release 4.07 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)