# fdim

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## 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



           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.1‐2017 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 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.
    
           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.
    


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