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Source file src/math/bits.go

Documentation: math

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package math
  
  const (
  	uvnan    = 0x7FF8000000000001
  	uvinf    = 0x7FF0000000000000
  	uvneginf = 0xFFF0000000000000
  	mask     = 0x7FF
  	shift    = 64 - 11 - 1
  	bias     = 1023
  )
  
  // Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
  func Inf(sign int) float64 {
  	var v uint64
  	if sign >= 0 {
  		v = uvinf
  	} else {
  		v = uvneginf
  	}
  	return Float64frombits(v)
  }
  
  // NaN returns an IEEE 754 ``not-a-number'' value.
  func NaN() float64 { return Float64frombits(uvnan) }
  
  // IsNaN reports whether f is an IEEE 754 ``not-a-number'' value.
  func IsNaN(f float64) (is bool) {
  	// IEEE 754 says that only NaNs satisfy f != f.
  	// To avoid the floating-point hardware, could use:
  	//	x := Float64bits(f);
  	//	return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
  	return f != f
  }
  
  // IsInf reports whether f is an infinity, according to sign.
  // If sign > 0, IsInf reports whether f is positive infinity.
  // If sign < 0, IsInf reports whether f is negative infinity.
  // If sign == 0, IsInf reports whether f is either infinity.
  func IsInf(f float64, sign int) bool {
  	// Test for infinity by comparing against maximum float.
  	// To avoid the floating-point hardware, could use:
  	//	x := Float64bits(f);
  	//	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
  	return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
  }
  
  // normalize returns a normal number y and exponent exp
  // satisfying x == y × 2**exp. It assumes x is finite and non-zero.
  func normalize(x float64) (y float64, exp int) {
  	const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
  	if Abs(x) < SmallestNormal {
  		return x * (1 << 52), -52
  	}
  	return x, 0
  }
  

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