man3/ceil.3

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  27 .TH CEIL 3  2017-09-15 "" "Linux Programmer's Manual"
  28 .SH NAME
  29 ceil, ceilf, ceill \- ceiling function: smallest integral value not
  30 less than argument
  31 .SH SYNOPSIS
  32 .nf
  33 .B #include <math.h>
  34 .PP
  35 .BI "double ceil(double " x );
  36 .BI "float ceilf(float " x );
  37 .BI "long double ceill(long double " x );
  38 .fi
  39 .PP
  40 Link with \fI\-lm\fP.
  41 .PP
  42 .in -4n
  43 Feature Test Macro Requirements for glibc (see
  44 .BR feature_test_macros (7)):
  45 .in
  46 .PP
  47 .ad l
  48 .BR ceilf (),
  49 .BR ceill ():
  50 .RS 4
  51 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  52     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  53     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  54 .RE
  55 .ad
  56 .SH DESCRIPTION
  57 These functions return the smallest integral value that is not less than
  58 .IR x .
  59 .PP
  60 For example,
  61 .IR ceil(0.5)
  62 is 1.0, and
  63 .IR ceil(\-0.5)
  64 is 0.0.
  65 .SH RETURN VALUE
  66 These functions return the ceiling of
  67 .IR x .
  68 .PP
  69 If
  70 .I x
  71 is integral, +0, \-0, NaN, or infinite,
  72 .I x
  73 itself is returned.
  74 .SH ERRORS
  75 No errors occur.
  76 POSIX.1-2001 documents a range error for overflows, but see NOTES.
  77 .SH ATTRIBUTES
  78 For an explanation of the terms used in this section, see
  79 .BR attributes (7).
  80 .TS
  81 allbox;
  82 lbw24 lb lb
  83 l l l.
  84 Interface       Attribute       Value
  85 T{
  86 .BR ceil (),
  87 .BR ceilf (),
  88 .BR ceill ()
  89 T}      Thread safety   MT-Safe
  90 .TE
  91 .SH CONFORMING TO
  92 C99, POSIX.1-2001, POSIX.1-2008.
  93 .PP
  94 The variant returning
  95 .I double
  96 also conforms to
  97 SVr4, 4.3BSD, C89.
  98 .SH NOTES
  99 SUSv2 and POSIX.1-2001 contain text about overflow (which might set
 100 .I errno
 101 to
 102 .BR ERANGE ,
 103 or raise an
 104 .B FE_OVERFLOW
 105 exception).
 106 In practice, the result cannot overflow on any current machine,
 107 so this error-handling stuff is just nonsense.
 108 .\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
 109 (More precisely, overflow can happen only when the maximum value
 110 of the exponent is smaller than the number of mantissa bits.
 111 For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
 112 the maximum value of the exponent is 128 (respectively, 1024),
 113 and the number of mantissa bits is 24 (respectively, 53).)
 114 .PP
 115 The integral value returned by these functions may be too large
 116 to store in an integer type
 117 .RI ( int ,
 118 .IR long ,
 119 etc.).
 120 To avoid an overflow, which will produce undefined results,
 121 an application should perform a range check on the returned value
 122 before assigning it to an integer type.
 123 .SH SEE ALSO
 124 .BR floor (3),
 125 .BR lrint (3),
 126 .BR nearbyint (3),
 127 .BR rint (3),
 128 .BR round (3),
 129 .BR trunc (3)