Source file src/pkg/math/sin.go

// 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) }