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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
func sinus(x float64, quad int) float64 {
// Coefficients are #3370 from Hart & Cheney (18.80D).
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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