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# Source file src/math/asin.go

## Documentation: math

```     1  // Copyright 2009 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
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  func Asin(x float64) float64 {
20  	if haveArchAsin {
21  		return archAsin(x)
22  	}
23  	return asin(x)
24  }
25
26  func asin(x float64) float64 {
27  	if x == 0 {
28  		return x // special case
29  	}
30  	sign := false
31  	if x < 0 {
32  		x = -x
33  		sign = true
34  	}
35  	if x > 1 {
36  		return NaN() // special case
37  	}
38
39  	temp := Sqrt(1 - x*x)
40  	if x > 0.7 {
41  		temp = Pi/2 - satan(temp/x)
42  	} else {
43  		temp = satan(x / temp)
44  	}
45
46  	if sign {
47  		temp = -temp
48  	}
49  	return temp
50  }
51
52  // Acos returns the arccosine, in radians, of x.
53  //
54  // Special case is:
55  //	Acos(x) = NaN if x < -1 or x > 1
56  func Acos(x float64) float64 {
57  	if haveArchAcos {
58  		return archAcos(x)
59  	}
60  	return acos(x)
61  }
62
63  func acos(x float64) float64 {
64  	return Pi/2 - Asin(x)
65  }
66
```

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