NAME¶
matherr - SVID math library exception handling
SYNOPSIS¶
#define _SVID_SOURCE /* See feature_test_macros(7) */
#include <math.h>
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
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 |
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 3.44 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/.