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>
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  26 .\"
  27 .\" References consulted:
  28 .\"     Linux libc source code
  29 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  30 .\"     386BSD man pages
  31 .\"
  32 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  33 .\" Modified 2002-08-10 Walter Harms
  34 .\"     (walter.harms@informatik.uni-oldenburg.de)
  35 .\" Modified 2003-11-18, 2004-10-05 aeb
  36 .\"
  37 .TH REMAINDER 3 2015-04-19 "" "Linux Programmer's Manual"
  38 .SH NAME
  39 drem, dremf, dreml, remainder, remainderf, remainderl \- \
  40 floating-point remainder function
  41 .SH SYNOPSIS
  42 .nf
  43 .B #include <math.h>
  44 .sp
  45 /* The C99 versions */
  46 .BI "double remainder(double " x ", double " y );
  47 .BI "float remainderf(float " x ", float " y );
  48 .BI "long double remainderl(long double " x ", long double " y );
  49 .sp
  50 /* Obsolete synonyms */
  51 .BI "double drem(double " x ", double " y );
  52 .BI "float dremf(float " x ", float " y );
  53 .BI "long double dreml(long double " x ", long double " y );
  54 .sp
  55 .fi
  56 Link with \fI\-lm\fP.
  57 .sp
  58 .in -4n
  59 Feature Test Macro Requirements for glibc (see
  60 .BR feature_test_macros (7)):
  61 .in
  62 .sp
  63 .ad l
  64 .BR remainder ():
  65 .RS 4
  66 _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  67 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED ||
  68 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  69 .br
  70 or
  71 .I cc\ -std=c99
  72 .RE
  73 .br
  74 .BR remainderf (),
  75 .BR remainderl ():
  76 .RS 4
  77 _BSD_SOURCE || _SVID_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  78 .br
  79 or
  80 .I cc\ -std=c99
  81 .RE
  82 .br
  83 .BR drem (),
  84 .BR dremf (),
  85 .BR dreml ():
  86 .RS 4
  87 _SVID_SOURCE || _BSD_SOURCE
  88 .RE
  89 .ad b
  90 .SH DESCRIPTION
  91 These
  92 functions compute the remainder of dividing
  93 .I x
  94 by
  95 .IR y .
  96 The return value is
  97 \fIx\fP\-\fIn\fP*\fIy\fP,
  98 where
  99 .I n
 100 is the value
 101 .IR "x\ /\ y" ,
 102 rounded to the nearest integer.
 103 If the absolute value of
 104 \fIx\fP\-\fIn\fP*\fIy\fP
 105 is 0.5,
 106 .I n
 107 is chosen to be even.
 108
 109 These functions are unaffected by the current rounding mode (see
 110 .BR fenv (3)).
 111 .LP
 112 The
 113 .BR drem ()
 114 function does precisely the same thing.
 115 .SH RETURN VALUE
 116 On success, these
 117 functions return the floating-point remainder,
 118 \fIx\fP\-\fIn\fP*\fIy\fP.
 119 If the return value is 0, it has the sign of
 120 .IR x .
 121
 122 If
 123 .I x
 124 or
 125 .I y
 126 is a NaN, a NaN is returned.
 127
 128 If
 129 .I x
 130 is an infinity,
 131 and
 132 .I y
 133 is not a NaN,
 134 a domain error occurs, and
 135 a NaN is returned.
 136
 137 If
 138 .I y
 139 is zero,
 140 .\" FIXME . Instead, glibc gives a domain error even if x is a NaN
 141 and
 142 .I x
 143 is not a NaN,
 144 .\" Interestingly, remquo(3) does not have the same problem.
 145 a domain error occurs, and
 146 a NaN is returned.
 147 .SH ERRORS
 148 See
 149 .BR math_error (7)
 150 for information on how to determine whether an error has occurred
 151 when calling these functions.
 152 .PP
 153 The following errors can occur:
 154 .TP
 155 Domain error: \fIx\fP is an infinity and \fIy\fP is not a NaN
 156 .\" .I errno
 157 .\" is set to
 158 .\" .BR EDOM .
 159 An invalid floating-point exception
 160 .RB ( FE_INVALID )
 161 is raised.
 162 .IP
 163 These functions do not set
 164 .IR errno
 165 for this case.
 166 .\" FIXME . Is it intentional that these functions do not set errno?
 167 .\" They do set errno for the y == 0 case, below.
 168 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6783
 169 .TP
 170 Domain error: \fIy\fP is zero\" [XXX see bug above] and \fIx\fP is not a NaN
 171 .I errno
 172 is set to
 173 .BR EDOM .
 174 An invalid floating-point exception
 175 .RB ( FE_INVALID )
 176 is raised.
 177 .SH ATTRIBUTES
 178 For an explanation of the terms used in this section, see
 179 .BR attributes (7).
 180 .TS
 181 allbox;
 182 lbw26 lb lb
 183 l l l.
 184 Interface       Attribute       Value
 185 T{
 186 .BR drem (),
 187 .BR dremf (),
 188 .BR dreml (),
 189 .br
 190 .BR remainder (),
 191 .BR remainderf (),
 192 .br
 193 .BR remainderl ()
 194 T}      Thread safety   MT-Safe
 195 .TE
 196 .SH CONFORMING TO
 197 .\" IEC 60559.
 198 The functions
 199 .BR remainder (),
 200 .BR remainderf (),
 201 and
 202 .BR remainderl ()
 203 are specified in C99, POSIX.1-2001, and POSIX.1-2008.
 204
 205 The function
 206 .BR drem ()
 207 is from 4.3BSD.
 208 The
 209 .I float
 210 and
 211 .I "long double"
 212 variants
 213 .BR dremf ()
 214 and
 215 .BR dreml ()
 216 exist on some systems, such as Tru64 and glibc2.
 217 Avoid the use of these functions in favor of
 218 .BR remainder ()
 219 etc.
 220 .SH BUGS
 221 The call
 222
 223     remainder(nan(""), 0);
 224
 225 returns a NaN, as expected, but wrongly causes a domain error;
 226 it should yield a silent NaN.
 227 .\" FIXME . this bug occurs as at glibc 2.8.
 228 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6779
 229 .SH EXAMPLE
 230 The call "remainder(29.0, 3.0)" returns \-1.
 231 .SH SEE ALSO
 232 .BR div (3),
 233 .BR fmod (3),
 234 .BR remquo (3)