matherr - SVID math library exception handling

#include<math.h>intmatherr(structexception*exc);extern_LIB_VERSION_TYPE_LIB_VERSION;Feature Test Macro Requirements for glibc (see(7)):feature_test_macrossignificand(),significandf(),significandl(): /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _SVID_SOURCE Link with-lm.

The System V Interface Definition (SVID) specifies that various math functions should invoke a function calledmatherr() if a math exception is detected. This function is called before the math function returns; aftermatherr() returns, the system then returns to the math function, which in turn returns to the caller. Thematherr() mechanism is supported by glibc, but is now obsolete: new applications should use the techniques described in(7) andmath_errorfenv(3). This page documents the glibcmatherr() mechanism as an aid for maintaining and porting older applications. To employmatherr(), the programmer must define the_SVID_SOURCEfeature test macro (before includinganyheader files), and assign the value_SVID_to the external variable_LIB_VERSION. The system provides a default version ofmatherr(). This version does nothing, and returns zero (see below for the significance of this). The defaultmatherr() 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 anexceptionstructure, 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 */ } Thetypefield has one of the following values:DOMAINA domain error occurred (the function argument was outside the range for which the function is defined). The return value depends on the function;errnois set toEDOM.SINGA pole error occurred (the function result is an infinity). The return value in most cases isHUGE(the largest single precision floating-point number), appropriately signed. In most cases,errnois set toEDOM.OVERFLOWAn overflow occurred. In most cases, the valueHUGEis returned, anderrnois set toERANGE.UNDERFLOWAn underflow occurred. 0.0 is returned, anderrnois set toERANGE.TLOSSTotal loss of significance. 0.0 is returned, anderrnois set toERANGE.PLOSSPartial loss of significance. This value is unused on glibc (and many other systems). Thearg1andarg2fields are the arguments supplied to the function (arg2is undefined for functions that take only one argument). Theretvalfield specifies the return value that the math function will return to its caller. The programmer-definedmatherr() can modify this field to change the return value of the math function. If thematherr() function returns zero, then the system setserrnoas described above, and may print an error message on standard error (see below). If thematherr() function returns a nonzero value, then the system does not seterrno, and doesn't print an error message.Mathfunctionsthatemploymatherr()The table below lists the functions and circumstances in whichmatherr() is called. The "Type" column indicates the value assigned toexc->typewhen callingmatherr(). The "Result" column is the default return value assigned toexc->retval. The "Msg?" and "errno" columns describe the default behavior ifmatherr() 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>FunctionTypeResultMsg?errnoacos(|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 ERANGEy0(0) DOMAIN -HUGE y EDOM y0(x<0) DOMAIN -HUGE y EDOMy1(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 EDOMlgamma(0) tgamma(fin) o/f OVERFLOW HUGE_VAL n ERANGE tgamma(-int) SING NAN y EDOMtgamma(0) SING copysign( y ERANGE HUGE_VAL,x)log(0) SING -HUGE y EDOM log(x<0) DOMAIN -HUGE y EDOMlog2(0) SING -HUGE n EDOM log2(x<0) DOMAIN -HUGE n EDOMlog10(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

For an explanation of the terms used in this section, seeattributes(7).InterfaceAttributeValuematherr() Thread safety MT-Safe

The example program demonstrates the use ofmatherr() when callinglog(3). The program takes up to three command-line arguments. The first argument is the floating-point number to be given tolog(3). If the optional second argument is provided, then_LIB_VERSIONis set to_SVID_so thatmatherr() is called, and the integer supplied in the command-line argument is used as the return value frommatherr(). If the optional third command-line argument is supplied, then it specifies an alternative return value thatmatherr() should assign as the return value of the math function. The following example run, wherelog(3) is given an argument of 0.0, does not usematherr(): $./a.out0.0errno: Numerical result out of range x=-inf In the following run,matherr() is called, and returns 0: $./a.out0.00matherr 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.out0.01matherr 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, anderrnowas not set. In the following run,matherr() is called, changes the return value of the math function, and returns a nonzero value: $./a.out0.0112345.0matherr SING exception in log() function args: 0.000000, 0.000000 retval: -340282346638528859811704183484516925440.000000 x=12345.000000Programsource#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); }

fenv(3),(7),math_errorstandards(7)

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