libgo/go/math/asin.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 arcsine and arccosine.
   9
  10         They are implemented by computing the arctangent
  11         after appropriate range reduction.
  12 */
  13
  14 // Asin returns the arcsine, in radians, of x.
  15 //
  16 // Special cases are:
  17 //      Asin(±0) = ±0
  18 //      Asin(x) = NaN if x < -1 or x > 1
  19
  20 //extern asin
  21 func libc_asin(float64) float64
  22
  23 func Asin(x float64) float64 {
  24         return libc_asin(x)
  25 }
  26
  27 func asin(x float64) float64 {
  28         if x == 0 {
  29                 return x // special case
  30         }
  31         sign := false
  32         if x < 0 {
  33                 x = -x
  34                 sign = true
  35         }
  36         if x > 1 {
  37                 return NaN() // special case
  38         }
  39
  40         temp := Sqrt(1 - x*x)
  41         if x > 0.7 {
  42                 temp = Pi/2 - satan(temp/x)
  43         } else {
  44                 temp = satan(x / temp)
  45         }
  46
  47         if sign {
  48                 temp = -temp
  49         }
  50         return temp
  51 }
  52
  53 // Acos returns the arccosine, in radians, of x.
  54 //
  55 // Special case is:
  56 //      Acos(x) = NaN if x < -1 or x > 1
  57
  58 //extern acos
  59 func libc_acos(float64) float64
  60
  61 func Acos(x float64) float64 {
  62         return libc_acos(x)
  63 }
  64
  65 func acos(x float64) float64 {
  66         return Pi/2 - Asin(x)
  67 }