Source file src/pkg/math/sincos.go
1 // Copyright 2010 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 package math
6
7 // Coefficients _sin[] and _cos[] are found in pkg/math/sin.go.
8
9 // Sincos(x) returns Sin(x), Cos(x).
10 //
11 // Special cases are:
12 // Sincos(±0) = ±0, 1
13 // Sincos(±Inf) = NaN, NaN
14 // Sincos(NaN) = NaN, NaN
15 func Sincos(x float64) (sin, cos float64)
16
17 func sincos(x float64) (sin, cos float64) {
18 const (
19 PI4A = 7.85398125648498535156E-1 // 0x3fe921fb40000000, Pi/4 split into three parts
20 PI4B = 3.77489470793079817668E-8 // 0x3e64442d00000000,
21 PI4C = 2.69515142907905952645E-15 // 0x3ce8469898cc5170,
22 M4PI = 1.273239544735162542821171882678754627704620361328125 // 4/pi
23 )
24 // special cases
25 switch {
26 case x == 0:
27 return x, 1 // return ±0.0, 1.0
28 case IsNaN(x) || IsInf(x, 0):
29 return NaN(), NaN()
30 }
31
32 // make argument positive
33 sinSign, cosSign := false, false
34 if x < 0 {
35 x = -x
36 sinSign = true
37 }
38
39 j := int64(x * M4PI) // integer part of x/(Pi/4), as integer for tests on the phase angle
40 y := float64(j) // integer part of x/(Pi/4), as float
41
42 if j&1 == 1 { // map zeros to origin
43 j += 1
44 y += 1
45 }
46 j &= 7 // octant modulo 2Pi radians (360 degrees)
47 if j > 3 { // reflect in x axis
48 j -= 4
49 sinSign, cosSign = !sinSign, !cosSign
50 }
51 if j > 1 {
52 cosSign = !cosSign
53 }
54
55 z := ((x - y*PI4A) - y*PI4B) - y*PI4C // Extended precision modular arithmetic
56 zz := z * z
57 cos = 1.0 - 0.5*zz + zz*zz*((((((_cos[0]*zz)+_cos[1])*zz+_cos[2])*zz+_cos[3])*zz+_cos[4])*zz+_cos[5])
58 sin = z + z*zz*((((((_sin[0]*zz)+_sin[1])*zz+_sin[2])*zz+_sin[3])*zz+_sin[4])*zz+_sin[5])
59 if j == 1 || j == 2 {
60 sin, cos = cos, sin
61 }
62 if cosSign {
63 cos = -cos
64 }
65 if sinSign {
66 sin = -sin
67 }
68 return
69 }