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32.\" from: @(#)exp.3 6.12 (Berkeley) 7/31/91
33.\" $Id: log.3,v 1.5 2004/12/20 21:35:45 scp Exp $
34.\"
35.Dd December 11, 2006
36.Dt LOG 3
37.Os BSD 4
38.Sh NAME
39.Nm log ,
40.Nm log2 ,
41.Nm log10 ,
42.Nm log1p ,
43.Nd logarithm functions
44.Sh SYNOPSIS
45.Fd #include <math.h>
46.Ft double
47.Fn log "double x"
48.Ft long double
49.Fn logl "long double x"
50.Ft float
51.Fn logf "float x"
52.Ft double
53.Fn log2 "double x"
54.Ft long double
55.Fn log2l "long double x"
56.Ft float
57.Fn log2f "float x"
58.Ft double
59.Fn log10 "double x"
60.Ft long double
61.Fn log10l "long double x"
62.Ft float
63.Fn log10f "float x"
64.Ft double
65.Fn log1p "double x"
66.Ft long double
67.Fn log1pl "long double x"
68.Ft float
69.Fn log1pf "float x"
70.Sh DESCRIPTION
71The
72.Fn log
73function computes the value of the natural logarithm of argument
74.Fa x.
75.Pp
76The
77.Fn log2
78function computes the value of the logarithm of argument
79.Fa x
80to base 2.
81.Pp
82The
83.Fn log10
84function computes the value of the logarithm of argument
85.Fa x
86to base 10.
87.Pp
88The
89.Fn log1p
90function computes
91the value of log(1+x) accurately even for very small values of
92.Fa x .
93.Sh SPECIAL VALUES
94.Fn log "�0"
95,
96.Fn log2 "�0"
97, and
98.Fn log10 "�0"
99return -infinity and raise the "divide-by-zero" floating-point exception.
100.Pp
101.Fn log "1"
102,
103.Fn log2 "1"
104, and
105.Fn log10 "1"
106return +0.
107.Pp
108.Fn log "x"
109,
110.Fn log2 "x"
111, and
112.Fn log10 "x"
113return a NaN and raise the "invalid" floating-point exception for x < 0.
114.Pp
115.Fn log "+infinity"
116,
117.Fn log2 "+infinity"
118, and
119.Fn log10 "+infinity"
120return +infinity.
121.Pp
122.Fn log1p "�0"
123returns �0.
124.Pp
125.Fn log1p "-1"
126returns -infinity and raises the "divide-by-zero" floating-point exception.
127.Pp
128.Fn log1p "x"
129returns a NaN and raises the "invalid" floating-point exception for x < -1.
130.Pp
131.Fn log1p "+infinity"
132returns +infinity.
133.Sh SEE ALSO
134.Xr math 3 ,
135.Xr exp 3 ,
136.Xr exp2 3 ,
137.Xr expm1 3 ,
138.Xr pow 3
139.Sh STANDARDS
140The
141.Fn log
142,
143.Fn log2
144,
145.Fn log10
146, and
147.Fn log1p
148functions conform to ISO/IEC 9899:1999(E).