man3/ceil.3

   1 .\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>.
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .TH CEIL 3  2021-03-22 GNU "Linux Programmer's Manual"
   8 .SH NAME
   9 ceil, ceilf, ceill \- ceiling function: smallest integral value not
  10 less than argument
  11 .SH LIBRARY
  12 Math library
  13 .RI ( libm ", " \-lm )
  14 .SH SYNOPSIS
  15 .nf
  16 .B #include <math.h>
  17 .PP
  18 .BI "double ceil(double " x );
  19 .BI "float ceilf(float " x );
  20 .BI "long double ceill(long double " x );
  21 .fi
  22 .PP
  23 .RS -4
  24 Feature Test Macro Requirements for glibc (see
  25 .BR feature_test_macros (7)):
  26 .RE
  27 .PP
  28 .BR ceilf (),
  29 .BR ceill ():
  30 .nf
  31     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  32         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  33         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  34 .fi
  35 .SH DESCRIPTION
  36 These functions return the smallest integral value that is not less than
  37 .IR x .
  38 .PP
  39 For example,
  40 .I ceil(0.5)
  41 is 1.0, and
  42 .I ceil(\-0.5)
  43 is 0.0.
  44 .SH RETURN VALUE
  45 These functions return the ceiling of
  46 .IR x .
  47 .PP
  48 If
  49 .I x
  50 is integral, +0, \-0, NaN, or infinite,
  51 .I x
  52 itself is returned.
  53 .SH ERRORS
  54 No errors occur.
  55 POSIX.1-2001 documents a range error for overflows, but see NOTES.
  56 .SH ATTRIBUTES
  57 For an explanation of the terms used in this section, see
  58 .BR attributes (7).
  59 .ad l
  60 .nh
  61 .TS
  62 allbox;
  63 lbx lb lb
  64 l l l.
  65 Interface       Attribute       Value
  66 T{
  67 .BR ceil (),
  68 .BR ceilf (),
  69 .BR ceill ()
  70 T}      Thread safety   MT-Safe
  71 .TE
  72 .hy
  73 .ad
  74 .sp 1
  75 .SH CONFORMING TO
  76 C99, POSIX.1-2001, POSIX.1-2008.
  77 .PP
  78 The variant returning
  79 .I double
  80 also conforms to
  81 SVr4, 4.3BSD, C89.
  82 .SH NOTES
  83 SUSv2 and POSIX.1-2001 contain text about overflow (which might set
  84 .I errno
  85 to
  86 .BR ERANGE ,
  87 or raise an
  88 .B FE_OVERFLOW
  89 exception).
  90 In practice, the result cannot overflow on any current machine,
  91 so this error-handling stuff is just nonsense.
  92 .\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
  93 (More precisely, overflow can happen only when the maximum value
  94 of the exponent is smaller than the number of mantissa bits.
  95 For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
  96 the maximum value of the exponent is 128 (respectively, 1024),
  97 and the number of mantissa bits is 24 (respectively, 53).)
  98 .PP
  99 The integral value returned by these functions may be too large
 100 to store in an integer type
 101 .RI ( int ,
 102 .IR long ,
 103 etc.).
 104 To avoid an overflow, which will produce undefined results,
 105 an application should perform a range check on the returned value
 106 before assigning it to an integer type.
 107 .SH SEE ALSO
 108 .BR floor (3),
 109 .BR lrint (3),
 110 .BR nearbyint (3),
 111 .BR rint (3),
 112 .BR round (3),
 113 .BR trunc (3)