bits.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  const (
     8  	uvnan    = 0x7FF8000000000001
     9  	uvinf    = 0x7FF0000000000000
    10  	uvneginf = 0xFFF0000000000000
    11  	uvone    = 0x3FF0000000000000
    12  	mask     = 0x7FF
    13  	shift    = 64 - 11 - 1
    14  	bias     = 1023
    15  	signMask = 1 << 63
    16  	fracMask = 1<<shift - 1
    17  )
    18  
    19  // Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
    20  func Inf(sign int) float64 {
    21  	var v uint64
    22  	if sign >= 0 {
    23  		v = uvinf
    24  	} else {
    25  		v = uvneginf
    26  	}
    27  	return Float64frombits(v)
    28  }
    29  
    30  // NaN returns an IEEE 754 “not-a-number” value.
    31  func NaN() float64 { return Float64frombits(uvnan) }
    32  
    33  // IsNaN reports whether f is an IEEE 754 “not-a-number” value.
    34  func IsNaN(f float64) (is bool) {
    35  	// IEEE 754 says that only NaNs satisfy f != f.
    36  	// To avoid the floating-point hardware, could use:
    37  	//	x := Float64bits(f);
    38  	//	return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
    39  	return f != f
    40  }
    41  
    42  // IsInf reports whether f is an infinity, according to sign.
    43  // If sign > 0, IsInf reports whether f is positive infinity.
    44  // If sign < 0, IsInf reports whether f is negative infinity.
    45  // If sign == 0, IsInf reports whether f is either infinity.
    46  func IsInf(f float64, sign int) bool {
    47  	// Test for infinity by comparing against maximum float.
    48  	// To avoid the floating-point hardware, could use:
    49  	//	x := Float64bits(f);
    50  	//	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
    51  	if sign == 0 {
    52  		f = Abs(f)
    53  	} else if sign < 0 {
    54  		f = -f
    55  	}
    56  	return f > MaxFloat64
    57  }
    58  
    59  // normalize returns a normal number y and exponent exp
    60  // satisfying x == y × 2**exp. It assumes x is finite and non-zero.
    61  func normalize(x float64) (y float64, exp int) {
    62  	const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
    63  	if Abs(x) < SmallestNormal {
    64  		return x * (1 << 52), -52
    65  	}
    66  	return x, 0
    67  }
    68
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