1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
|
'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\" Linux libc source code
.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\" 386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-07-27 by Walter Harms
.\" (walter.harms@informatik.uni-oldenburg.de)
.\"
.TH fmod 3 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
fmod, fmodf, fmodl \- floating-point remainder function
.SH LIBRARY
Math library
.RI ( libm ", " \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.P
.BI "double fmod(double " x ", double " y );
.BI "float fmodf(float " x ", float " y );
.BI "long double fmodl(long double " x ", long double " y );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR fmodf (),
.BR fmodl ():
.nf
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
These functions compute the floating-point remainder of dividing
.I x
by
.IR y .
The return value is
.I x
\-
.I n
*
.IR y ,
where
.I n
is the quotient of
.I x
/
.IR y ,
rounded toward zero to an integer.
.P
To obtain the modulus, more specifically, the Least Positive Residue,
you will need to adjust the result from fmod like so:
.P
.in +4n
.nf
z = fmod(x, y);
if (z < 0)
z += y;
.fi
.in
.P
An alternate way to express this is with
.IR "fmod(fmod(x, y) + y, y)" ,
but the second
.BR fmod ()
usually costs way more than the one branch.
.SH RETURN VALUE
On success, these
functions return the value \fIx\fP\ \-\ \fIn\fP*\fIy\fP,
for some integer
.IR n ,
such that the returned value has the same sign as
.I x
and a magnitude less than the magnitude of
.IR y .
.P
If
.I x
or
.I y
is a NaN, a NaN is returned.
.P
If
.I x
is an infinity,
a domain error occurs, and
a NaN is returned.
.P
If
.I y
is zero,
a domain error occurs, and
a NaN is returned.
.P
If
.I x
is +0 (\-0), and
.I y
is not zero, +0 (\-0) is returned.
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.P
The following errors can occur:
.TP
Domain error: \fIx\fP is an infinity
.I errno
is set to
.B EDOM
(but see BUGS).
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.TP
Domain error: \fIy\fP is zero
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.\" POSIX.1 documents an optional underflow error, but AFAICT it doesn't
.\" (can't?) occur -- mtk, Jul 2008
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR fmod (),
.BR fmodf (),
.BR fmodl ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
C99, POSIX.1-2001.
.P
The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH BUGS
Before glibc 2.10, the glibc implementation did not set
.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6784
.I errno
to
.B EDOM
when a domain error occurred for an infinite
.IR x .
.SH EXAMPLES
The call
.I fmod(372, 360)
returns 348.
.P
The call
.I fmod(-372, 360)
returns -12.
.P
The call
.I fmod(-372, -360)
also returns -12.
.SH SEE ALSO
.BR remainder (3)
|
