ceil(3)                    Library Functions Manual                    ceil(3)

NAME
       ceil, ceilf, ceill - ceiling function: smallest integral value not less
       than argument

LIBRARY
       Math library (libm, -lm)

SYNOPSIS
       #include <math.h>

       double ceil(double x);
       float ceilf(float x);
       long double ceill(long double x);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       ceilf(), ceill():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       These functions return the smallest integral value that is not less
       than x.

       For example, ceil(0.5) is 1.0, and ceil(-0.5) is 0.0.

RETURN VALUE
       These functions return the ceiling of x.

       If x is integral, +0, -0, NaN, or infinite, x itself is returned.

ERRORS
       No errors occur.  POSIX.1-2001 documents a range error for overflows,
       but see NOTES.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |ceil (), ceilf (), ceill ()                 | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       C99, POSIX.1-2001.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

NOTES
       SUSv2 and POSIX.1-2001 contain text about overflow (which might set
       errno to ERANGE, or raise an FE_OVERFLOW exception).  In practice, the
       result cannot overflow on any current machine, so this error-handling
       stuff is just nonsense.  (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 127 (respectively,
       1023), and the number of mantissa bits including the implicit bit is 24
       (respectively, 53).)

       The integral value returned by these functions may be too large to
       store in an integer type (int, 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.

SEE ALSO
       floor(3), lrint(3), nearbyint(3), rint(3), round(3), trunc(3)

Linux man-pages 6.7               2023-10-31                           ceil(3)