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// 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 sine and cosine.
Coefficients are #5077 from Hart & Cheney. (18.80D)
*/
func sinus(x float64, quad int) float64 {
const (
P0 = .1357884097877375669092680e8
P1 = -.4942908100902844161158627e7
P2 = .4401030535375266501944918e6
P3 = -.1384727249982452873054457e5
P4 = .1459688406665768722226959e3
Q0 = .8644558652922534429915149e7
Q1 = .4081792252343299749395779e6
Q2 = .9463096101538208180571257e4
Q3 = .1326534908786136358911494e3
)
if x < 0 {
x = -x
quad = quad + 2
}
x = x * (2 / Pi) /* underflow? */
var y float64
if x > 32764 {
var e float64
e, y = Modf(x)
e = e + float64(quad)
f, _ := Modf(0.25 * e)
quad = int(e - 4*f)
} else {
k := int32(x)
y = x - float64(k)
quad = (quad + int(k)) & 3
}
if quad&1 != 0 {
y = 1 - y
}
if quad > 1 {
y = -y
}
yy := y * y
temp1 := ((((P4*yy+P3)*yy+P2)*yy+P1)*yy + P0) * y
temp2 := ((((yy+Q3)*yy+Q2)*yy+Q1)*yy + Q0)
return temp1 / temp2
}
// Cos returns the cosine of x.
func Cos(x float64) float64 {
if x < 0 {
x = -x
}
return sinus(x, 1)
}
// Sin returns the sine of x.
func Sin(x float64) float64 { return sinus(x, 0) }
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