Source file src/pkg/math/sin.go

     1	// Copyright 2009 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	/*
     8		Floating-point sine and cosine.
     9	
    10		Coefficients are #5077 from Hart & Cheney. (18.80D)
    11	*/
    12	
    13	func sinus(x float64, quad int) float64 {
    14		const (
    15			P0 = .1357884097877375669092680e8
    16			P1 = -.4942908100902844161158627e7
    17			P2 = .4401030535375266501944918e6
    18			P3 = -.1384727249982452873054457e5
    19			P4 = .1459688406665768722226959e3
    20			Q0 = .8644558652922534429915149e7
    21			Q1 = .4081792252343299749395779e6
    22			Q2 = .9463096101538208180571257e4
    23			Q3 = .1326534908786136358911494e3
    24		)
    25		if x < 0 {
    26			x = -x
    27			quad = quad + 2
    28		}
    29		x = x * (2 / Pi) /* underflow? */
    30		var y float64
    31		if x > 32764 {
    32			var e float64
    33			e, y = Modf(x)
    34			e = e + float64(quad)
    35			f, _ := Modf(0.25 * e)
    36			quad = int(e - 4*f)
    37		} else {
    38			k := int32(x)
    39			y = x - float64(k)
    40			quad = (quad + int(k)) & 3
    41		}
    42	
    43		if quad&1 != 0 {
    44			y = 1 - y
    45		}
    46		if quad > 1 {
    47			y = -y
    48		}
    49	
    50		yy := y * y
    51		temp1 := ((((P4*yy+P3)*yy+P2)*yy+P1)*yy + P0) * y
    52		temp2 := ((((yy+Q3)*yy+Q2)*yy+Q1)*yy + Q0)
    53		return temp1 / temp2
    54	}
    55	
    56	// Cos returns the cosine of x.
    57	func Cos(x float64) float64 {
    58		if x < 0 {
    59			x = -x
    60		}
    61		return sinus(x, 1)
    62	}
    63	
    64	// Sin returns the sine of x.
    65	func Sin(x float64) float64 { return sinus(x, 0) }
The Go Programming Language

Source file src/pkg/math/sin.go
