man-pages/man3/ceil.3

.\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>.
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.TH CEIL 3  2008-08-05 "" "Linux Programmer's Manual"
.SH NAME
ceil, ceilf, ceill \- ceiling function: smallest integral value not
less than argument
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "double ceil(double " x );
.br
.BI "float ceilf(float " x );
.br
.BI "long double ceill(long double " x );
.fi
.sp
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR ceilf (),
.BR ceill ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.ad b
.SH DESCRIPTION
These functions return the smallest integral value that is not less than
.IR x .

For example,
.IR ceil(0.5)
is 1.0, and
.IR ceil(\-0.5)
is 0.0.
.SH "RETURN VALUE"
These functions return the ceiling of
.IR x .

If \fIx\fP is integral, +0, \-0, NaN, or infinite,
\fIx\fP itself is returned.
.SH ERRORS
No errors occur.
POSIX.1-2001 documents a "range error" for overflows, but see NOTES.
.SH "CONFORMING TO"
C99, POSIX.1-2001.
The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH NOTES
SUSv2 and POSIX.1-2001 contain text about overflow (which might set
.I errno
to
.BR ERANGE ,
or raise an
.B FE_OVERFLOW
exception).
In practice, the result cannot overflow on any current machine,
so this error-handling stuff is just nonsense.
.\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
(More precisely, overflow can happen only when the maximum value
of the exponent is smaller than the number of mantissa bits.
For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
the maximum value of the exponent is 128 (respectively, 1024),
and the number of mantissa bits is 24 (respectively, 53).)

The integral value returned by these functions may be too large
to store in an integer type
.RI ( int ,
.IR long ,
etc.).
To avoid an overflow, which will produce undefined results,
an application should perform a range check on the returned value
before assigning it to an integer type.
.SH "SEE ALSO"
.BR floor (3),
.BR lrint (3),
.BR nearbyint (3),
.BR rint (3),
.BR round (3),
.BR trunc (3)