bits.mx raw

   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  	return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
  52  }
  53  
  54  // normalize returns a normal number y and exponent exp
  55  // satisfying x == y × 2**exp. It assumes x is finite and non-zero.
  56  func normalize(x float64) (y float64, exp int) {
  57  	const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
  58  	if Abs(x) < SmallestNormal {
  59  		return x * (1 << 52), -52
  60  	}
  61  	return x, 0
  62  }
  63