# Source file src/math/ldexp.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  // Ldexp is the inverse of [Frexp].
8  // It returns frac × 2**exp.
9  //
10  // Special cases are:
11  //
12  //	Ldexp(±0, exp) = ±0
13  //	Ldexp(±Inf, exp) = ±Inf
14  //	Ldexp(NaN, exp) = NaN
15  func Ldexp(frac float64, exp int) float64 {
16  	if haveArchLdexp {
17  		return archLdexp(frac, exp)
18  	}
19  	return ldexp(frac, exp)
20  }
21
22  func ldexp(frac float64, exp int) float64 {
23  	// special cases
24  	switch {
25  	case frac == 0:
26  		return frac // correctly return -0
27  	case IsInf(frac, 0) || IsNaN(frac):
28  		return frac
29  	}
30  	frac, e := normalize(frac)
31  	exp += e
32  	x := Float64bits(frac)
33  	exp += int(x>>shift)&mask - bias
34  	if exp < -1075 {
35  		return Copysign(0, frac) // underflow
36  	}
37  	if exp > 1023 { // overflow
38  		if frac < 0 {
39  			return Inf(-1)
40  		}
41  		return Inf(1)
42  	}
43  	var m float64 = 1
44  	if exp < -1022 { // denormal
45  		exp += 53
46  		m = 1.0 / (1 << 53) // 2**-53
47  	}
48  	x &^= mask << shift
49  	x |= uint64(exp+bias) << shift
50  	return m * Float64frombits(x)
51  }
52
```

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