The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> fmod, fmodf, fmodl - floating-point remainder value function

#### SYNOPSIS

> ``#include <math.h>
> double fmod(double` x`, double` y`);
> float fmodf(float` x`, float` y`);
> long double fmodl(long double` x`, long double` y`);
> ``

#### DESCRIPTION

> [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 return the floating-point remainder of the division of x by y.

> An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

#### RETURN VALUE

> These functions shall return the value x- i* y, for some integer i such that, if y is non-zero, the result has the same sign as x and magnitude less than the magnitude of y.

> If the correct value would cause underflow, [MXX] and is not representable, a range error may occur, and fmod(), modf(), and fmodl() shall return [MXX] 0.0, or (if the IEC 60559 Floating-Point option is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

> [MX] If x or y is NaN, a NaN shall be returned, and none of the conditions below shall be considered.

> If y is zero, a domain error shall occur, and a NaN shall be returned.

> If x is infinite, a domain error shall occur, and a NaN shall be returned.

> If x is ±0 and y is not zero, ±0 shall be returned.

> If x is not infinite and y is ±Inf, x shall be returned.

> [MXX] If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

#### ERRORS

> These functions shall fail if:

> Domain Error
>   [MX] The x argument is infinite or y is zero.

>   If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

> These functions may fail if:

> Range Error
>   The result underflows.

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

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> 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.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> feclearexcept, fetestexcept, isnan

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

#### CHANGE HISTORY

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

#### Issue 5

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

#### Issue 6

> The behavior for when the y argument is zero is now defined.

> The fmodf() and fmodl() functions are added for alignment with the ISO/IEC 9899:1999 standard.

> 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.

#### Issue 7

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0151 [68], XSH/TC1-2008/0152 [320], and XSH/TC1-2008/0153 [68] are applied.

> POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0120 [605] is applied.

End of informative text.

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