float.go

     1  // Copyright 2017 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 runtime
     6  
     7  import "unsafe"
     8  
     9  var inf = float64frombits(0x7FF0000000000000)
    10  
    11  // isNaN reports whether f is an IEEE 754 “not-a-number” value.
    12  func isNaN(f float64) (is bool) {
    13  	// IEEE 754 says that only NaNs satisfy f != f.
    14  	return f != f
    15  }
    16  
    17  // isFinite reports whether f is neither NaN nor an infinity.
    18  func isFinite(f float64) bool {
    19  	return !isNaN(f - f)
    20  }
    21  
    22  // isInf reports whether f is an infinity.
    23  func isInf(f float64) bool {
    24  	return !isNaN(f) && !isFinite(f)
    25  }
    26  
    27  // abs returns the absolute value of x.
    28  //
    29  // Special cases are:
    30  //
    31  //	abs(±Inf) = +Inf
    32  //	abs(NaN) = NaN
    33  func abs(x float64) float64 {
    34  	const sign = 1 << 63
    35  	return float64frombits(float64bits(x) &^ sign)
    36  }
    37  
    38  // copysign returns a value with the magnitude
    39  // of x and the sign of y.
    40  func copysign(x, y float64) float64 {
    41  	const sign = 1 << 63
    42  	return float64frombits(float64bits(x)&^sign | float64bits(y)&sign)
    43  }
    44  
    45  // float64bits returns the IEEE 754 binary representation of f.
    46  func float64bits(f float64) uint64 {
    47  	return *(*uint64)(unsafe.Pointer(&f))
    48  }
    49  
    50  // float64frombits returns the floating point number corresponding
    51  // the IEEE 754 binary representation b.
    52  func float64frombits(b uint64) float64 {
    53  	return *(*float64)(unsafe.Pointer(&b))
    54  }
    55
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