LROUND(3P) POSIX Programmer's Manual LROUND(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
lround, lroundf, lroundl -- round to nearest integer value
SYNOPSIS
#include <math.h>
long lround(double x);
long lroundf(float x);
long lroundl(long double x);
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.1-2008 defers to the ISO C standard.
These functions shall round their argument to the nearest integer value, rounding halfway cases away from zero, regardless of the current
rounding direction.
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 rounded integer value.
If x is NaN, a domain error shall occur and an unspecified value is returned.
If x is +Inf, a domain error shall occur and an unspecified value is returned.
If x is -Inf, a domain error shall occur and an unspecified value is returned.
If the correct value is positive and too large to represent as a long, an unspecified value shall be returned. On systems that support the
IEC 60559 Floating-Point option, a domain shall occur; otherwise, a domain error may occur.
If the correct value is negative and too large to represent as a long, an unspecified value shall be returned. On systems that support the
IEC 60559 Floating-Point option, a domain shall occur; otherwise, a domain error may occur.
ERRORS
These functions shall fail if:
Domain Error
The x argument is NaN or +-Inf, or the correct value is not representable as an integer.
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:
Domain Error
The correct value is not representable as an integer.
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.
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
These functions differ from the lrint() functions in the default rounding direction, with the lround() functions rounding halfway cases
away from zero and needing not to raise the inexact floating-point exception for non-integer arguments that round to within the range of
the return type.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept(), fetestexcept(), llround()
The Base Definitions volume of POSIX.1-2008, Section 4.19, 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, 2013 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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 .
IEEE
/The Open Group 2013 LROUND(3P)