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
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. tanh.c Hyperbolic tangent SYNOPSIS: double x, y, tanh(); y = tanh( x ); DESCRIPTION: Returns hyperbolic tangent of argument in the range MINLOG to MAXLOG. MAXLOG = 8.8029691931113054295988e+01 = log(2**127) MINLOG = -8.872283911167299960540e+01 = log(2**-128) A rational function is used for |x| < 0.625. The form x + x**3 P(x)/Q(x) of Cody & Waite is employed. Otherwise, tanh(x) = sinh(x)/cosh(x) = 1 - 2/(exp(2x) + 1). ACCURACY: Relative error: arithmetic domain # trials peak rms IEEE -2,2 30000 2.5e-16 5.8e-17 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

var tanhP = [...]float64{
	-9.64399179425052238628e-1,
	-9.92877231001918586564e1,
	-1.61468768441708447952e3,
}
var tanhQ = [...]float64{
	1.12811678491632931402e2,
	2.23548839060100448583e3,
	4.84406305325125486048e3,
}
Tanh returns the hyperbolic tangent of x. Special cases are: Tanh(±0) = ±0 Tanh(±Inf) = ±1 Tanh(NaN) = NaN
func ( float64) float64

func ( float64) float64 {
	const  = 8.8029691931113054295988e+01 // log(2**127)
	 := Abs()
	switch {
	case  > 0.5*:
		if  < 0 {
			return -1
		}
		return 1
	case  >= 0.625:
		 := Exp(2 * )
		 = 1 - 2/(+1)
		if  < 0 {
			 = -
		}
	default:
		if  == 0 {
			return 
		}
		 :=  * 
		 =  + **((tanhP[0]*+tanhP[1])*+tanhP[2])/(((+tanhQ[0])*+tanhQ[1])*+tanhQ[2])
	}
	return