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>
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  25 .TH ROUND 3  2008-08-05 "" "Linux Programmer's Manual"
  26 .SH NAME
  27 round, roundf, roundl \- round to nearest integer, away from zero
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <math.h>
  31 .sp
  32 .BI "double round(double " x );
  33 .br
  34 .BI "float roundf(float " x );
  35 .br
  36 .BI "long double roundl(long double " x );
  37 .fi
  38 .sp
  39 Link with \fI\-lm\fP.
  40 .sp
  41 .in -4n
  42 Feature Test Macro Requirements for glibc (see
  43 .BR feature_test_macros (7)):
  44 .in
  45 .sp
  46 .ad l
  47 .BR round (),
  48 .BR roundf (),
  49 .BR roundl ():
  50 _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
  51 .I cc\ -std=c99
  52 .ad b
  53 .SH DESCRIPTION
  54 These functions round \fIx\fP to the nearest integer, but
  55 round halfway cases away from zero (regardless of the current rounding
  56 direction), instead of to the nearest even integer like
  57 .BR rint (3).
  58
  59 For example,
  60 .IR round(0.5)
  61 is 1.0, and
  62 .IR round(\-0.5)
  63 is \-1.0.
  64 .SH "RETURN VALUE"
  65 These functions return the rounded integer value.
  66
  67 If \fIx\fP is integral, +0, \-0, NaN,  or infinite,
  68 \fIx\fP itself is returned.
  69 .SH ERRORS
  70 No errors occur.
  71 POSIX.1-2001 documents a "range error" for overflows, but see NOTES.
  72 .SH "CONFORMING TO"
  73 C99, POSIX.1-2001.
  74 .SH NOTES
  75 POSIX.1-2001 contains text about overflow (which might set
  76 .I errno
  77 to
  78 .BR ERANGE ,
  79 or raise an
  80 .B FE_OVERFLOW
  81 exception).
  82 In practice, the result cannot overflow on any current machine,
  83 so this error-handling stuff is just nonsense.
  84 .\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
  85 (More precisely, overflow can happen only when the maximum value
  86 of the exponent is smaller than the number of mantissa bits.
  87 For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
  88 the maximum value of the exponent is 128 (respectively, 1024),
  89 and the number of mantissa bits is 24 (respectively, 53).)
  90
  91 If you want to store the rounded value in an integer type,
  92 you probably want to use one of the functions described in
  93 .BR lround (3)
  94 instead.
  95 .SH "SEE ALSO"
  96 .BR ceil (3),
  97 .BR floor (3),
  98 .BR lround (3),
  99 .BR nearbyint (3),
 100 .BR rint (3),
 101 .BR trunc (3)