man3/remainder.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
   4 .\"
   5 .\" Permission is granted to make and distribute verbatim copies of this
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  13 .\"
  14 .\" Since the Linux kernel and libraries are constantly changing, this
  15 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  16 .\" responsibility for errors or omissions, or for damages resulting from
  17 .\" the use of the information contained herein.  The author(s) may not
  18 .\" have taken the same level of care in the production of this manual,
  19 .\" which is licensed free of charge, as they might when working
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  22 .\" Formatted or processed versions of this manual, if unaccompanied by
  23 .\" the source, must acknowledge the copyright and authors of this work.
  24 .\"
  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\"
  30 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  31 .\" Modified 2002-08-10 Walter Harms
  32 .\"     (walter.harms@informatik.uni-oldenburg.de)
  33 .\" Modified 2003-11-18, 2004-10-05 aeb
  34 .\"
  35 .TH REMAINDER 3 2009-02-04 "" "Linux Programmer's Manual"
  36 .SH NAME
  37 drem, dremf, dreml, remainder, remainderf, remainderl \- \
  38 floating-point remainder function
  39 .SH SYNOPSIS
  40 .nf
  41 .B #include <math.h>
  42 .sp
  43 /* The C99 versions */
  44 .BI "double remainder(double " x ", double " y );
  45 .BI "float remainderf(float " x ", float " y );
  46 .BI "long double remainderl(long double " x ", long double " y );
  47 .sp
  48 /* Obsolete synonyms */
  49 .BI "double drem(double " x ", double " y );
  50 .BI "float dremf(float " x ", float " y );
  51 .BI "long double dreml(long double " x ", long double " y );
  52 .sp
  53 .fi
  54 Link with \fI\-lm\fP.
  55 .sp
  56 .in -4n
  57 Feature Test Macro Requirements for glibc (see
  58 .BR feature_test_macros (7)):
  59 .in
  60 .sp
  61 .ad l
  62 .BR remainder ():
  63 _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE; or
  64 .I cc\ -std=c99
  65 .br
  66 .BR remainderf (),
  67 .BR remainderl ():
  68 _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
  69 .I cc\ -std=c99
  70 .br
  71 .BR drem (),
  72 .BR dremf (),
  73 .BR dreml ():
  74 _SVID_SOURCE || _BSD_SOURCE
  75 .ad b
  76 .SH DESCRIPTION
  77 The
  78 .BR remainder ()
  79 function computes the remainder of dividing
  80 .I x
  81 by
  82 .IR y .
  83 The return value is
  84 \fIx\fP\-\fIn\fP*\fIy\fP,
  85 where
  86 .I n
  87 is the value
  88 .IR "x\ /\ y" ,
  89 rounded to the nearest integer.
  90 If the absolute value of
  91 \fIx\fP\-\fIn\fP*\fIy\fP
  92 is 0.5,
  93 .I n
  94 is chosen to be even.
  95
  96 These functions are unaffected by the current rounding mode (see
  97 .BR fenv (3)).
  98 .LP
  99 The
 100 .BR drem ()
 101 function does precisely the same thing.
 102 .SH "RETURN VALUE"
 103 On success, these
 104 functions return the floating-point remainder,
 105 \fIx\fP\-\fIn\fP*\fIy\fP.
 106 If the return value is 0, it has the sign of
 107 .IR x .
 108
 109 If
 110 .I x
 111 or
 112 .I y
 113 is a NaN, a NaN is returned.
 114
 115 If
 116 .I x
 117 is an infinity,
 118 and
 119 .I y
 120 is not a NaN,
 121 a domain error occurs, and
 122 a NaN is returned.
 123
 124 If
 125 .I y
 126 is zero,
 127 .\" FIXME . Instead, glibc gives a domain error even if x is a NaN
 128 and
 129 .I x
 130 is not a NaN,
 131 .\" Interestingly, remquo(3) does not have the same problem.
 132 a domain error occurs, and
 133 a NaN is returned.
 134 .SH ERRORS
 135 See
 136 .BR math_error (7)
 137 for information on how to determine whether an error has occurred
 138 when calling these functions.
 139 .PP
 140 The following errors can occur:
 141 .TP
 142 Domain error: \fIx\fP is an infinity and \fIy\fP is not a NaN
 143 .\" .I errno
 144 .\" is set to
 145 .\" .BR EDOM .
 146 An invalid floating-point exception
 147 .RB ( FE_INVALID )
 148 is raised.
 149 .IP
 150 These functions do not set
 151 .IR errno
 152 for this case.
 153 .\" FIXME . Is it intentional that these functions do not set errno?
 154 .\" They do set errno for the y == 0 case, below.
 155 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6783
 156 .TP
 157 Domain error: \fIy\fP is zero\" [XXX see bug above] and \fIx\fP is not a NaN
 158 .I errno
 159 is set to
 160 .BR EDOM .
 161 An invalid floating-point exception
 162 .RB ( FE_INVALID )
 163 is raised.
 164 .SH "CONFORMING TO"
 165 .\" IEC 60559.
 166 The functions
 167 .BR remainder (),
 168 .BR remainderf (),
 169 and
 170 .BR remainderl ()
 171 are specified in C99 and POSIX.1-2001.
 172
 173 The function
 174 .BR drem ()
 175 is from 4.3BSD.
 176 The
 177 .I float
 178 and
 179 .I "long double"
 180 variants
 181 .BR dremf ()
 182 and
 183 .BR dreml ()
 184 exist on some systems, such as Tru64 and glibc2.
 185 Avoid the use of these functions in favor of
 186 .BR remainder ()
 187 etc.
 188 .SH BUGS
 189 The call
 190
 191     remainder(nan(""), 0);
 192
 193 returns a NaN, as expected, but wrongly causes a domain error;
 194 it should yield a silent NaN.
 195 .\" FIXME . this bug occurs as at glibc 2.8.
 196 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6779
 197 .SH EXAMPLE
 198 The call "remainder(29.0, 3.0)" returns \-1.
 199 .SH "SEE ALSO"
 200 .BR div (3),
 201 .BR fmod (3),
 202 .BR remquo (3)