matherr (3)
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Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
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NAME
matherr - SVID math library exception handlingSYNOPSIS
#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 |
| -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 |
| 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 |
| 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 |
| For an explanation of the terms used in this section, see | ||||
| allbox; | ||||
| lb lb lb | ||||
| l l l. | ||||
| 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 functionaqs 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); }