blob: 43990fe40fe5b214894b5e2e2b108cff5a64a0c8 (
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
|
// 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
/*
* floating-point arctangent
*
* atan returns the value of the arctangent of its
* argument in the range [-pi/2,pi/2].
* there are no error returns.
* coefficients are #5077 from Hart & Cheney. (19.56D)
*/
const
(
p4 = .161536412982230228262e2;
p3 = .26842548195503973794141e3;
p2 = .11530293515404850115428136e4;
p1 = .178040631643319697105464587e4;
p0 = .89678597403663861959987488e3;
q4 = .5895697050844462222791e2;
q3 = .536265374031215315104235e3;
q2 = .16667838148816337184521798e4;
q1 = .207933497444540981287275926e4;
q0 = .89678597403663861962481162e3;
pio2 = .15707963267948966192313216e1;
pio4 = .7853981633974483096156608e0;
sq2p1 = .2414213562373095048802e1; // sqrt(2)+1
sq2m1 = .414213562373095048802e0; // sqrt(2)-1
)
/*
* xatan evaluates a series valid in the
* range [-0.414...,+0.414...]. (tan(pi/8))
*/
func Xatan(arg float64) float64 {
argsq := arg*arg;
value := ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);
value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);
return value*arg;
}
/*
* satan reduces its argument (known to be positive)
* to the range [0,0.414...] and calls xatan.
*/
func Satan(arg float64) float64 {
if arg < sq2m1 {
return Xatan(arg);
}
if arg > sq2p1 {
return pio2 - Xatan(1/arg);
}
return pio4 + Xatan((arg-1)/(arg+1));
}
/*
* atan makes its argument positive and
* calls the inner routine satan.
*/
export func Atan(arg float64) float64 {
if arg > 0 {
return Satan(arg);
}
return -Satan(-arg);
}
|
