blob: 96b3d96956cba34478f2b361b63b69b74d6d3473 (
plain)
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
|
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
export log, log10
/*
log returns the natural logarithm of its floating
point argument.
The coefficients are #2705 from Hart & Cheney. (19.38D)
It calls frexp.
*/
const
(
log2 = .693147180559945309e0;
ln10o1 = .4342944819032518276511;
sqrto2 = .707106781186547524e0;
p0 = -.240139179559210510e2;
p1 = .309572928215376501e2;
p2 = -.963769093377840513e1;
p3 = .421087371217979714e0;
q0 = -.120069589779605255e2;
q1 = .194809660700889731e2;
q2 = -.891110902798312337e1;
)
func
log(arg double) double
{
var x, z, zsq, temp double;
var exp int;
if arg <= 0 {
return sys.NaN();
}
x,exp = sys.frexp(arg);
for x < 0.5 {
x = x*2;
exp = exp-1;
}
if x < sqrto2 {
x = x*2;
exp = exp-1;
}
z = (x-1) / (x+1);
zsq = z*z;
temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0;
temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0);
temp = temp*z + double(exp)*log2;
return temp;
}
func
log10(arg double) double
{
if arg <= 0 {
return sys.NaN();
}
return log(arg) * ln10o1;
}
|
