math: atan2 special cases (negative zero)
Added Signbit(), revised Copysign()
R=rsc
CC=golang-dev
https://golang.org/cl/822045
diff --git a/src/pkg/math/atan2.go b/src/pkg/math/atan2.go
index a738fbc..49d4bdd 100644
--- a/src/pkg/math/atan2.go
+++ b/src/pkg/math/atan2.go
@@ -11,8 +11,10 @@
// Special cases are (in order):
// Atan2(y, NaN) = NaN
// Atan2(NaN, x) = NaN
-// Atan2(0, x>=0) = 0
-// Atan2(0, x<0) = Pi
+// 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
@@ -32,41 +34,29 @@
case y != y || x != x: // IsNaN(y) || IsNaN(x):
return NaN()
case y == 0:
- if x >= 0 {
- return 0
+ if x >= 0 && !Signbit(x) {
+ return Copysign(0, y)
}
- return Pi
+ return Copysign(Pi, y)
case x == 0:
- if y > 0 {
- return Pi / 2
- }
- return -Pi / 2
+ return Copysign(Pi/2, y)
case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0):
if x > MaxFloat64 { // IsInf(x, 1) {
switch {
- case y > MaxFloat64: // IsInf(y, 1):
- return Pi / 4
- case y < -MaxFloat64: // IsInf(y, -1):
- return -Pi / 4
+ case y < -MaxFloat64 || y > MaxFloat64: // IsInf(y, -1) || IsInf(y, 1):
+ return Copysign(Pi/4, y)
default:
- return 0
+ return Copysign(0, y)
}
}
switch {
- case y > MaxFloat64: //IsInf(y, 1):
- return 3 * Pi / 4
- case y < -MaxFloat64: //IsInf(y, -1):
- return -3 * Pi / 4
- case y > 0:
- return Pi
+ case y < -MaxFloat64 || y > MaxFloat64: // IsInf(y, -1) || IsInf(y, 1):
+ return Copysign(3*Pi/4, y)
default:
- return -Pi
+ return Copysign(Pi, y)
}
case y < -MaxFloat64 || y > MaxFloat64: //IsInf(y, 0):
- if y > MaxFloat64 { // IsInf(y, 1) {
- return Pi / 2
- }
- return -Pi / 2
+ return Copysign(Pi/2, y)
}
// Call atan and determine the quadrant.
