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Source file src/math/atan2.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
  
  // Atan2 returns the arc tangent of y/x, using
  // the signs of the two to determine the quadrant
  // of the return value.
  //
  // Special cases are (in order):
  //	Atan2(y, NaN) = NaN
  //	Atan2(NaN, x) = NaN
  //	Atan2(+0, x>=0) = +0
  //	Atan2(-0, x>=0) = -0
  //	Atan2(+0, x<=-0) = +Pi
  //	Atan2(-0, x<=-0) = -Pi
  //	Atan2(y>0, 0) = +Pi/2
  //	Atan2(y<0, 0) = -Pi/2
  //	Atan2(+Inf, +Inf) = +Pi/4
  //	Atan2(-Inf, +Inf) = -Pi/4
  //	Atan2(+Inf, -Inf) = 3Pi/4
  //	Atan2(-Inf, -Inf) = -3Pi/4
  //	Atan2(y, +Inf) = 0
  //	Atan2(y>0, -Inf) = +Pi
  //	Atan2(y<0, -Inf) = -Pi
  //	Atan2(+Inf, x) = +Pi/2
  //	Atan2(-Inf, x) = -Pi/2
  func Atan2(y, x float64) float64
  
  func atan2(y, x float64) float64 {
  	// special cases
  	switch {
  	case IsNaN(y) || IsNaN(x):
  		return NaN()
  	case y == 0:
  		if x >= 0 && !Signbit(x) {
  			return Copysign(0, y)
  		}
  		return Copysign(Pi, y)
  	case x == 0:
  		return Copysign(Pi/2, y)
  	case IsInf(x, 0):
  		if IsInf(x, 1) {
  			switch {
  			case IsInf(y, 0):
  				return Copysign(Pi/4, y)
  			default:
  				return Copysign(0, y)
  			}
  		}
  		switch {
  		case IsInf(y, 0):
  			return Copysign(3*Pi/4, y)
  		default:
  			return Copysign(Pi, y)
  		}
  	case IsInf(y, 0):
  		return Copysign(Pi/2, y)
  	}
  
  	// Call atan and determine the quadrant.
  	q := Atan(y / x)
  	if x < 0 {
  		if q <= 0 {
  			return q + Pi
  		}
  		return q - Pi
  	}
  	return q
  }
  

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