IEEE Std 1003.1-2008

Copyright © 2001-2008 The IEEE and The Open Group

erfc, erfcf, erfcl - complementary error functions

#include <math.h>

double erfc(doublex);

float erfcf(floatx);

long double erfcl(long doublex);

^{[CX]}The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.These functions shall compute the complementary error function 1.0 -

erf(x).An application wishing to check for error situations should set

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the value of the complementary error function.

If the correct value would cause underflow and is not representable, a range error may occur and

^{[MX]}either 0.0 (if representable), or an implementation-defined value shall be returned.

^{[MX]}Ifxis NaN, a NaN shall be returned.If

xis ±0, +1 shall be returned.If

xis -Inf, +2 shall be returned.If

xis +Inf, +0 shall be returned.If the correct value would cause underflow and is representable, a range error may occur and the correct value shall be returned.

These functions may fail if:

- Range Error
- The result underflows.
If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall be set to [ERANGE]. If the integer expression (math_errhandling& MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

None.

The

erfc() function is provided because of the extreme loss of relative accuracy iferf(x) is called for largexand the result subtracted from 1.0.Note for IEEE Std 754-1985

double, 26.55 <ximplieserfc(x) has underflowed.On error, the expressions (

math_errhandling& MATH_ERRNO) and (math_errhandling& MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

None.

None.

erf,feclearexcept,fetestexcept,isnanXBD

Treatment of Error Conditions for Mathematical Functions,<math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

The

erfc() function is no longer marked as an extension.These functions are split out from the

erf() reference page.The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

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