FDIM(3) Library Functions Manual FDIM(3)

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

#include <math.h>

double fdim(double x, double y);
float fdimf(float x, float y);
long double fdiml(long double x, long double y);

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 IEEE Std 1003.1-2001 (“POSIX.1”) 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 (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

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 (), (), and () shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

If x - y is positive and underflows, a range error may occur, and either ( x - y) (if representable), or 0.0 (if supported), or an implementation-defined value shall be returned.

If x or y is NaN, a NaN shall be returned.

The fdim () function shall fail if:

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:

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.

None.

On implementations supporting IEEE Std 754-1985, x - y cannot underflow, and hence the 0.0 return value is shaded as an extension for implementations supporting the XSI extension rather than an MX extension.

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.

feclearexcept(3), fetestexcept(3), fmax(3), fmin(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), xbd_chap04(7), <math.h>

First released in Issue 6. Derived from the ISO/IEC 9899:1999 (“ISO C99”) standard.

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January 1, 2004 posix.fail