/usr/share/go-1.6/src/math/tan.go is in golang-1.6-src 1.6.1-0ubuntu1.
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The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 | // Copyright 2011 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 tangent.
*/
// The original C code, the long comment, and the constants
// below were from http://netlib.sandia.gov/cephes/cmath/sin.c,
// available from http://www.netlib.org/cephes/cmath.tgz.
// The go code is a simplified version of the original C.
//
// tan.c
//
// Circular tangent
//
// SYNOPSIS:
//
// double x, y, tan();
// y = tan( x );
//
// DESCRIPTION:
//
// Returns the circular tangent of the radian argument x.
//
// Range reduction is modulo pi/4. A rational function
// x + x**3 P(x**2)/Q(x**2)
// is employed in the basic interval [0, pi/4].
//
// ACCURACY:
// Relative error:
// arithmetic domain # trials peak rms
// DEC +-1.07e9 44000 4.1e-17 1.0e-17
// IEEE +-1.07e9 30000 2.9e-16 8.1e-17
//
// Partial loss of accuracy begins to occur at x = 2**30 = 1.074e9. The loss
// is not gradual, but jumps suddenly to about 1 part in 10e7. Results may
// be meaningless for x > 2**49 = 5.6e14.
// [Accuracy loss statement from sin.go comments.]
//
// Cephes Math Library Release 2.8: June, 2000
// Copyright 1984, 1987, 1989, 1992, 2000 by Stephen L. Moshier
//
// The readme file at http://netlib.sandia.gov/cephes/ says:
// Some software in this archive may be from the book _Methods and
// Programs for Mathematical Functions_ (Prentice-Hall or Simon & Schuster
// International, 1989) or from the Cephes Mathematical Library, a
// commercial product. In either event, it is copyrighted by the author.
// What you see here may be used freely but it comes with no support or
// guarantee.
//
// The two known misprints in the book are repaired here in the
// source listings for the gamma function and the incomplete beta
// integral.
//
// Stephen L. Moshier
// moshier@na-net.ornl.gov
// tan coefficients
var _tanP = [...]float64{
-1.30936939181383777646E4, // 0xc0c992d8d24f3f38
1.15351664838587416140E6, // 0x413199eca5fc9ddd
-1.79565251976484877988E7, // 0xc1711fead3299176
}
var _tanQ = [...]float64{
1.00000000000000000000E0,
1.36812963470692954678E4, //0x40cab8a5eeb36572
-1.32089234440210967447E6, //0xc13427bc582abc96
2.50083801823357915839E7, //0x4177d98fc2ead8ef
-5.38695755929454629881E7, //0xc189afe03cbe5a31
}
// Tan returns the tangent of the radian argument x.
//
// Special cases are:
// Tan(±0) = ±0
// Tan(±Inf) = NaN
// Tan(NaN) = NaN
func Tan(x float64) float64
func tan(x float64) float64 {
const (
PI4A = 7.85398125648498535156E-1 // 0x3fe921fb40000000, Pi/4 split into three parts
PI4B = 3.77489470793079817668E-8 // 0x3e64442d00000000,
PI4C = 2.69515142907905952645E-15 // 0x3ce8469898cc5170,
M4PI = 1.273239544735162542821171882678754627704620361328125 // 4/pi
)
// special cases
switch {
case x == 0 || IsNaN(x):
return x // return ±0 || NaN()
case IsInf(x, 0):
return NaN()
}
// make argument positive but save the sign
sign := false
if x < 0 {
x = -x
sign = true
}
j := int64(x * M4PI) // integer part of x/(Pi/4), as integer for tests on the phase angle
y := float64(j) // integer part of x/(Pi/4), as float
/* map zeros and singularities to origin */
if j&1 == 1 {
j += 1
y += 1
}
z := ((x - y*PI4A) - y*PI4B) - y*PI4C
zz := z * z
if zz > 1e-14 {
y = z + z*(zz*(((_tanP[0]*zz)+_tanP[1])*zz+_tanP[2])/((((zz+_tanQ[1])*zz+_tanQ[2])*zz+_tanQ[3])*zz+_tanQ[4]))
} else {
y = z
}
if j&2 == 2 {
y = -1 / y
}
if sign {
y = -y
}
return y
}
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