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  15 .\" manual page may be incorrect or out-of-date.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  2008-07-29 "" "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.
  97 .LP
  98 The
  99 .BR drem ()
 100 function does precisely the same thing.
 101 .SH "RETURN VALUE"
 102 On success, these
 103 functions return the floating-point remainder,
 104 \fIx\fP\-\fIn\fP*\fIy\fP.
 105 If the return value is 0, it has the sign of
 106 .IR x .
 107
 108 If
 109 .I x
 110 or
 111 .I y
 112 is a NaN, a NaN is returned.
 113
 114 If
 115 .I x
 116 is an infinity,
 117 and
 118 .I y
 119 is not a NaN,
 120 a "domain error" occurs, and
 121 a NaN is returned.
 122
 123 If
 124 .I y
 125 is zero,
 126 .\" FIXME . Instead, glibc gives a domain error even if x is a NaN
 127 and
 128 .I x
 129 is not a NaN,
 130 .\" Interestingly, remquo(3) does not have the same problem.
 131 a "domain error" occurs, and
 132 a NaN is returned.
 133 .SH ERRORS
 134 See
 135 .BR math_error (7)
 136 for information on how to determine whether an error has occurred
 137 when calling these functions.
 138 .PP
 139 The following errors can occur:
 140 .TP
 141 Domain error: \fIx\fP is an infinity and \fIy\fP is not a NaN
 142 .\" .I errno
 143 .\" is set to
 144 .\" .BR EDOM .
 145 An invalid floating-point exception
 146 .RB ( FE_INVALID )
 147 is raised.
 148 .IP
 149 These functions do not set
 150 .IR errno
 151 for this case.
 152 .\" FIXME . Is it intentional that these functions do not set errno?
 153 .\" They do set errno for the y == 0 case, below.
 154 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6783
 155 .TP
 156 Domain error: \fIy\fP is zero\" [XXX see bug above] and \fIx\fP is not a NaN
 157 .I errno
 158 is set to
 159 .BR EDOM .
 160 An invalid floating-point exception
 161 .RB ( FE_INVALID )
 162 is raised.
 163 .SH "CONFORMING TO"
 164 .\" IEC 60559.
 165 The functions
 166 .BR remainder (),
 167 .BR remainderf (),
 168 and
 169 .BR remainderl ()
 170 are specified in C99 and POSIX.1-2001.
 171
 172 The function
 173 .BR drem ()
 174 is from 4.3BSD.
 175 The
 176 .I float
 177 and
 178 .I "long double"
 179 variants
 180 .BR dremf ()
 181 and
 182 .BR dreml ()
 183 exist on some systems, such as Tru64 and glibc2.
 184 Avoid the use of these functions in favor of
 185 .BR remainder ()
 186 etc.
 187 .SH EXAMPLE
 188 The call "remainder(29.0, 3.0)" returns \-1.
 189 .SH BUGS
 190 The call
 191
 192     remainder(nan(""), 0);
 193
 194 returns a NaN, as expected, but wrongly causes a domain error;
 195 it should yield a silent NaN.
 196 .\" FIXME . this bug occurs as at glibc 2.8.
 197 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6779
 198 .SH "SEE ALSO"
 199 .BR fmod (3),
 200 .BR remquo (3)