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CEIL(3) Linux Programmer's Manual CEIL(3)

NAME

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

SYNOPSIS

     #include <math.h>

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

     Link with -lm.

 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 versions <= 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).

     allbox;  lbw24  lb  lb  l  l  l.   Interface Attribute Value T{ ceil(),
     ceilf(), ceill() T}   Thread safety  MT-Safe

CONFORMING TO

     C99, POSIX.1-2001, POSIX.1-2008.

     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  man-
     tissa 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 (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.