github.com/miolini/go@v0.0.0-20160405192216-fca68c8cb408/src/runtime/complex.go (about)

     1  // Copyright 2010 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  func isposinf(f float64) bool { return f > maxFloat64 }
     8  func isneginf(f float64) bool { return f < -maxFloat64 }
     9  func isnan(f float64) bool    { return f != f }
    10  
    11  func nan() float64 {
    12  	var f float64 = 0
    13  	return f / f
    14  }
    15  
    16  func posinf() float64 {
    17  	var f float64 = maxFloat64
    18  	return f * f
    19  }
    20  
    21  func neginf() float64 {
    22  	var f float64 = maxFloat64
    23  	return -f * f
    24  }
    25  
    26  func complex128div(n complex128, d complex128) complex128 {
    27  	// Special cases as in C99.
    28  	ninf := isposinf(real(n)) || isneginf(real(n)) ||
    29  		isposinf(imag(n)) || isneginf(imag(n))
    30  	dinf := isposinf(real(d)) || isneginf(real(d)) ||
    31  		isposinf(imag(d)) || isneginf(imag(d))
    32  
    33  	nnan := !ninf && (isnan(real(n)) || isnan(imag(n)))
    34  	dnan := !dinf && (isnan(real(d)) || isnan(imag(d)))
    35  
    36  	switch {
    37  	case nnan || dnan:
    38  		return complex(nan(), nan())
    39  	case ninf && !dinf:
    40  		return complex(posinf(), posinf())
    41  	case !ninf && dinf:
    42  		return complex(0, 0)
    43  	case real(d) == 0 && imag(d) == 0:
    44  		if real(n) == 0 && imag(n) == 0 {
    45  			return complex(nan(), nan())
    46  		} else {
    47  			return complex(posinf(), posinf())
    48  		}
    49  	default:
    50  		// Standard complex arithmetic, factored to avoid unnecessary overflow.
    51  		a := real(d)
    52  		if a < 0 {
    53  			a = -a
    54  		}
    55  		b := imag(d)
    56  		if b < 0 {
    57  			b = -b
    58  		}
    59  		if a <= b {
    60  			ratio := real(d) / imag(d)
    61  			denom := real(d)*ratio + imag(d)
    62  			return complex((real(n)*ratio+imag(n))/denom,
    63  				(imag(n)*ratio-real(n))/denom)
    64  		} else {
    65  			ratio := imag(d) / real(d)
    66  			denom := imag(d)*ratio + real(d)
    67  			return complex((imag(n)*ratio+real(n))/denom,
    68  				(imag(n)-real(n)*ratio)/denom)
    69  		}
    70  	}
    71  }