man3/round.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 ROUND 3 2021-03-22 GNU "Linux Programmer's Manual"
   8 .SH NAME
   9 round, roundf, roundl \- round to nearest integer, away from zero
  10 .SH LIBRARY
  11 Math library
  12 .RI ( libm ", " \-lm )
  13 .SH SYNOPSIS
  14 .nf
  15 .B #include <math.h>
  16 .PP
  17 .BI "double round(double " x );
  18 .BI "float roundf(float " x );
  19 .BI "long double roundl(long double " x );
  20 .fi
  21 .PP
  22 .RS -4
  23 Feature Test Macro Requirements for glibc (see
  24 .BR feature_test_macros (7)):
  25 .RE
  26 .PP
  27 .BR round (),
  28 .BR roundf (),
  29 .BR roundl ():
  30 .nf
  31     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  32 .fi
  33 .SH DESCRIPTION
  34 These functions round
  35 .I x
  36 to the nearest integer, but
  37 round halfway cases away from zero (regardless of the current rounding
  38 direction, see
  39 .BR fenv (3)),
  40 instead of to the nearest even integer like
  41 .BR rint (3).
  42 .PP
  43 For example,
  44 .I round(0.5)
  45 is 1.0, and
  46 .I round(\-0.5)
  47 is \-1.0.
  48 .SH RETURN VALUE
  49 These functions return the rounded integer value.
  50 .PP
  51 If
  52 .I x
  53 is integral, +0, \-0, NaN, or infinite,
  54 .I x
  55 itself is returned.
  56 .SH ERRORS
  57 No errors occur.
  58 POSIX.1-2001 documents a range error for overflows, but see NOTES.
  59 .SH VERSIONS
  60 These functions first appeared in glibc in version 2.1.
  61 .SH ATTRIBUTES
  62 For an explanation of the terms used in this section, see
  63 .BR attributes (7).
  64 .ad l
  65 .nh
  66 .TS
  67 allbox;
  68 lbx lb lb
  69 l l l.
  70 Interface       Attribute       Value
  71 T{
  72 .BR round (),
  73 .BR roundf (),
  74 .BR roundl ()
  75 T}      Thread safety   MT-Safe
  76 .TE
  77 .hy
  78 .ad
  79 .sp 1
  80 .SH CONFORMING TO
  81 C99, POSIX.1-2001, POSIX.1-2008.
  82 .SH NOTES
  83 POSIX.1-2001 contains 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 If you want to store the rounded value in an integer type,
 100 you probably want to use one of the functions described in
 101 .BR lround (3)
 102 instead.
 103 .SH SEE ALSO
 104 .BR ceil (3),
 105 .BR floor (3),
 106 .BR lround (3),
 107 .BR nearbyint (3),
 108 .BR rint (3),
 109 .BR trunc (3)