66 lines
1.3 KiB
Go
66 lines
1.3 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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/*
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Floating-point sine and cosine.
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Coefficients are #5077 from Hart & Cheney. (18.80D)
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*/
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func sinus(x float64, quad int) float64 {
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const (
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P0 = .1357884097877375669092680e8
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P1 = -.4942908100902844161158627e7
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P2 = .4401030535375266501944918e6
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P3 = -.1384727249982452873054457e5
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P4 = .1459688406665768722226959e3
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Q0 = .8644558652922534429915149e7
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Q1 = .4081792252343299749395779e6
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Q2 = .9463096101538208180571257e4
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Q3 = .1326534908786136358911494e3
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)
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if x < 0 {
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x = -x
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quad = quad + 2
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}
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x = x * (2 / Pi) /* underflow? */
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var y float64
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if x > 32764 {
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var e float64
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e, y = Modf(x)
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e = e + float64(quad)
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f, _ := Modf(0.25 * e)
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quad = int(e - 4*f)
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} else {
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k := int32(x)
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y = x - float64(k)
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quad = (quad + int(k)) & 3
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}
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if quad&1 != 0 {
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y = 1 - y
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}
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if quad > 1 {
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y = -y
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}
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yy := y * y
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temp1 := ((((P4*yy+P3)*yy+P2)*yy+P1)*yy + P0) * y
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temp2 := ((((yy+Q3)*yy+Q2)*yy+Q1)*yy + Q0)
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return temp1 / temp2
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}
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// Cos returns the cosine of x.
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func Cos(x float64) float64 {
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if x < 0 {
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x = -x
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}
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return sinus(x, 1)
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}
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// Sin returns the sine of x.
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func Sin(x float64) float64 { return sinus(x, 0) }
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