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

#### NAME

> fdim, fdimf, fdiml - compute positive difference between two floating-point numbers

#### SYNOPSIS

> ``#include <math.h>
> double fdim(double` x`, double` y`);
> float fdimf(float` x`, float` y`);
> long double fdiml(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 determine the positive difference between their arguments. If x is greater than y, x- y is returned. If x is less than or equal to y, +0 is returned.

> 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

> Upon successful completion, these functions shall return the positive difference value.

> If x- y is positive and overflows, a range error shall occur and fdim(), fdimf(), and fdiml() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

> If the correct value would cause underflow, a range error may occur, and fdim(), fdimf(), and fdiml() shall return [MXX] the correct value, 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.

#### ERRORS

> The fdim() function shall fail if:

> Range Error
>   The result overflows.

>   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 overflow floating-point exception shall be raised.

> The fdim() function 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, fmax, fmin

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

#### CHANGE HISTORY

> First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

#### Issue 7

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0119 [68,428] and XSH/TC1-2008/0120 [68,428] are applied.

End of informative text.

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