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.

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.

       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 was 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).)  This was removed in POSIX.1-2008.

       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)