NAME
matherr - SVID math library exception handling SYNOPSIS
#define SVIDSOURCE /* See featuretestmacros(7) */
#include
int matherr(struct exception *exc); extern LIBVERSIONTYPE LIBVERSION; 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 matherror(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 SVIDSOURCE fea‐ ture test macro (before including any header files), and assign the value SVID to the external variable LIBVERSION. 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 XTLOSS is a constant defined in
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 HUGEVAL : -HUGEVAL 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|>XTLOSS) TLOSS 0.0 y ERANGE j1(|x|>XTLOSS) TLOSS 0.0 y ERANGE jn(|x|>XTLOSS) TLOSS 0.0 y ERANGE y0(x>XTLOSS) TLOSS 0.0 y ERANGE y1(x>XTLOSS) TLOSS 0.0 y ERANGE yn(x>XTLOSS) 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 HUGEVAL n ERANGE
tgamma(-int) SING NAN y EDOM tgamma(0) SING copysign( y ERANGE HUGEVAL,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 HUGEVAL :
-HUGEVAL 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 LIBVERSION 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 SVIDSOURCE
#include
#include
#include
#include
static int matherrret = 0; /* Value that matherr() should return */ static int changeretval = 0; /* Should matherr() change function's return value? */ static double newretval; /* 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 (changeretval)
exc->retval = newretval; return matherrret; } int main(int argc, char *argv[]) { double x; if (argc < 2) {
fprintf(stderr, "Usage: %s
" " [
[ ]]\n", argv[0]); exit(EXITFAILURE); } if (argc > 2) { LIBVERSION = SVID; matherrret = atoi(argv[2]); } if (argc > 3) { changeretval = 1; newretval = atof(argv[3]); } x = log(atof(argv[1])); if (errno != 0) perror("errno"); printf("x=%f\n", x); exit(EXITSUCCESS); } SEE ALSO fenv(3), matherror(7), standards(7) COLOPHON
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Linux 2010-09-10 MATHERR(3)