github.com/prattmic/llgo-embedded@v0.0.0-20150820070356-41cfecea0e1e/third_party/gofrontend/libgo/go/math/sincos.go (about)

     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 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  	return sincos(x)
    17  }
    18  
    19  func sincos(x float64) (sin, cos float64) {
    20  	const (
    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
    25  	)
    26  	// special cases
    27  	switch {
    28  	case x == 0:
    29  		return x, 1 // return ±0.0, 1.0
    30  	case IsNaN(x) || IsInf(x, 0):
    31  		return NaN(), NaN()
    32  	}
    33  
    34  	// make argument positive
    35  	sinSign, cosSign := false, false
    36  	if x < 0 {
    37  		x = -x
    38  		sinSign = true
    39  	}
    40  
    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
    43  
    44  	if j&1 == 1 { // map zeros to origin
    45  		j += 1
    46  		y += 1
    47  	}
    48  	j &= 7     // octant modulo 2Pi radians (360 degrees)
    49  	if j > 3 { // reflect in x axis
    50  		j -= 4
    51  		sinSign, cosSign = !sinSign, !cosSign
    52  	}
    53  	if j > 1 {
    54  		cosSign = !cosSign
    55  	}
    56  
    57  	z := ((x - y*PI4A) - y*PI4B) - y*PI4C // Extended precision modular arithmetic
    58  	zz := z * z
    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])
    61  	if j == 1 || j == 2 {
    62  		sin, cos = cos, sin
    63  	}
    64  	if cosSign {
    65  		cos = -cos
    66  	}
    67  	if sinSign {
    68  		sin = -sin
    69  	}
    70  	return
    71  }