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.
7 // Coefficients _sin[] and _cos[] are found in pkg/math/sin.go.
9 // Sincos(x) returns Sin(x), Cos(x).
13 // Sincos(±Inf) = NaN, NaN
14 // Sincos(NaN) = NaN, NaN
15 func Sincos(x float64) (sin, cos float64) {
19 func sincos(x float64) (sin, cos float64) {
21 PI4A = 7.85398125648498535156E-1 // 0x3fe921fb40000000, Pi/4 split into three parts
22 PI4B = 3.77489470793079817668E-8 // 0x3e64442d00000000,
23 PI4C = 2.69515142907905952645E-15 // 0x3ce8469898cc5170,
24 M4PI = 1.273239544735162542821171882678754627704620361328125 // 4/pi
29 return x, 1 // return ±0.0, 1.0
30 case IsNaN(x) || IsInf(x, 0):
34 // make argument positive
35 sinSign, cosSign := false, false
41 j := int64(x * M4PI) // integer part of x/(Pi/4), as integer for tests on the phase angle
42 y := float64(j) // integer part of x/(Pi/4), as float
44 if j&1 == 1 { // map zeros to origin
48 j &= 7 // octant modulo 2Pi radians (360 degrees)
49 if j > 3 { // reflect in x axis
51 sinSign, cosSign = !sinSign, !cosSign
57 z := ((x - y*PI4A) - y*PI4B) - y*PI4C // Extended precision modular arithmetic
59 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])
60 sin = z + z*zz*((((((_sin[0]*zz)+_sin[1])*zz+_sin[2])*zz+_sin[3])*zz+_sin[4])*zz+_sin[5])