github.com/peggyl/go@v0.0.0-20151008231540-ae315999c2d5/src/math/bits.go (about)

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