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32.\" from: @(#)ieee.3 6.4 (Berkeley) 5/6/91
33.\" $FreeBSD: src/lib/msun/man/ilogb.3,v 1.3 2005/11/17 13:00:00 ru Exp $
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35.Dd November 6, 2005
36.Dt ILOGB 3
37.Os
38.Sh NAME
39.Nm ilogb ,
40.Nm ilogbf ,
41.Nm ilogbl ,
42.Nm logb ,
43.Nm logbf
44.Nd extract exponent
45.Sh LIBRARY
46.Lb libm
47.Sh SYNOPSIS
48.In math.h
49.Ft int
50.Fn ilogb "double x"
51.Ft int
52.Fn ilogbf "float x"
53.Ft int
54.Fn ilogbl "long double x"
55.Ft double
56.Fn logb "double x"
57.Ft float
58.Fn logbf "float x"
59.Sh DESCRIPTION
60.Fn ilogb ,
61.Fn ilogbf
62and
63.Fn ilogbl
64return
65.Fa x Ns 's exponent
66in integer format.
67.Fn ilogb \*(Pm\*(If
68returns
69.Dv INT_MAX ,
70.Fn ilogb \*(Pm\*(Na
71returns
72.Dv FP_ILOGBNAN ,
73and
74.Fn ilogb 0
75returns
76.Dv FP_ILOGB0 .
77.Pp
78.Fn logb x
79and
80.Fn logbf x
81return
82.Fa x Ns 's exponent
83in floating\-point format with the same precision as
84.Fa x .
85.Fn logb \*(Pm\*(If
86returns +\*(If, and
87.Fn logb 0
88returns -\*(If with a division by zero exception.
89.Sh SEE ALSO
90.Xr frexp 3 ,
91.Xr ieee 3 ,
92.Xr math 3 ,
93.Xr scalbn 3
94.Sh STANDARDS
95The
96.Fn ilogb ,
97.Fn ilogbf ,
98.Fn ilogbl ,
99.Fn logb
100and
101.Fn logbf
102routines conform to
103.St -isoC-99 .
104.Fn logb
105and
106.Fn logbf
107implement the logb function recommended by
108.St -ieee754 .
109.Sh HISTORY
110The
111.Fn logb
112function appeared in
113.Bx 4.3 .
114The
115.Fn ilogb
116function appeared in
117.Fx 1.1.5 .
118The
119.Fn ilogbf
120and
121.Fn logbf
122functions appeared in
123.Fx 2.0 .
124The
125.Fn ilogbl
126function appeared in
127.Fx 5.4 .