...
Run Format

Source file src/math/asinh.go

  // Copyright 2010 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 are from FreeBSD's /usr/src/lib/msun/src/s_asinh.c
  // and came with this notice. The go code is a simplified
  // version of the original C.
  //
  // ====================================================
  // Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  //
  // Developed at SunPro, a Sun Microsystems, Inc. business.
  // Permission to use, copy, modify, and distribute this
  // software is freely granted, provided that this notice
  // is preserved.
  // ====================================================
  //
  //
  // asinh(x)
  // Method :
  //	Based on
  //	        asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
  //	we have
  //	asinh(x) := x  if  1+x*x=1,
  //	         := sign(x)*(log(x)+ln2)) for large |x|, else
  //	         := sign(x)*log(2|x|+1/(|x|+sqrt(x*x+1))) if|x|>2, else
  //	         := sign(x)*log1p(|x| + x**2/(1 + sqrt(1+x**2)))
  //
  
  // Asinh returns the inverse hyperbolic sine of x.
  //
  // Special cases are:
  //	Asinh(±0) = ±0
  //	Asinh(±Inf) = ±Inf
  //	Asinh(NaN) = NaN
  func Asinh(x float64) float64 {
  	const (
  		Ln2      = 6.93147180559945286227e-01 // 0x3FE62E42FEFA39EF
  		NearZero = 1.0 / (1 << 28)            // 2**-28
  		Large    = 1 << 28                    // 2**28
  	)
  	// special cases
  	if IsNaN(x) || IsInf(x, 0) {
  		return x
  	}
  	sign := false
  	if x < 0 {
  		x = -x
  		sign = true
  	}
  	var temp float64
  	switch {
  	case x > Large:
  		temp = Log(x) + Ln2 // |x| > 2**28
  	case x > 2:
  		temp = Log(2*x + 1/(Sqrt(x*x+1)+x)) // 2**28 > |x| > 2.0
  	case x < NearZero:
  		temp = x // |x| < 2**-28
  	default:
  		temp = Log1p(x + x*x/(1+Sqrt(1+x*x))) // 2.0 > |x| > 2**-28
  	}
  	if sign {
  		temp = -temp
  	}
  	return temp
  }
  

View as plain text