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table of contents

FDIM(3P) | POSIX Programmer's Manual | FDIM(3P) |

# 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(doublex, doubley); float fdimf(floatx, floaty); long double fdiml(long doublex, long doubley);

# 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.

# SEE ALSO¶

* feclearexcept()*,

*,*

*fetestexcept*()*,*

*fmax*()

*fmin*()*Section 4.20*, *Treatment of Error Conditions for
Mathematical Functions*, **<math.h>**

# COPYRIGHT¶

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

2017 | IEEE/The Open Group |