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types/geo: fix floating point bug causing NaN returns in SphericalAngleTo (#18777)

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Subtle floating point imprecision can propagate and lead to
trigonometric functions receiving inputs outside their
domain, thus returning NaN. Clamp the input to the valid domain
to prevent this.

Also adds a fuzz test for SphericalAngleTo.

Updates tailscale/corp#37518

Signed-off-by: Amal Bansode <amal@tailscale.com>
This commit is contained in:
Amal Bansode
2026-03-02 17:33:57 -08:00
committed by GitHub
parent 5a2168da9e
commit 8fd02bb626
2 changed files with 92 additions and 58 deletions
Download Patch File Download Diff File Expand all files Collapse all files
types/geo/point.go
+3
View File
@@ -125,6 +125,9 @@ func (p Point) SphericalAngleTo(q Point) (Radians, error) {
sLat, sLng := float64(qLat.Radians()), float64(qLng.Radians())
cosA := math.Sin(rLat)*math.Sin(sLat) +
math.Cos(rLat)*math.Cos(sLat)*math.Cos(rLng-sLng)
// Subtle floating point imprecision can lead to cosA being outside
// the domain of arccosine [-1, 1]. Clamp the input to avoid NaN return.
cosA = min(max(-1.0, cosA), 1.0)
return Radians(math.Acos(cosA)), nil
}
types/geo/point_test.go
+89 -58
View File
@@ -448,65 +448,79 @@ func TestPointMarshalUint64(t *testing.T) {
})
}
const earthRadius = 6371.000 // volumetric mean radius (km)
const kmToRad = 1 / earthRadius
// Test corpus for exercising PointSphericalAngleTo.
var corpusPointSphericalAngleTo = []struct {
name string
x geo.Point
y geo.Point
want geo.Radians
wantErr string
}{
{
name: "same-point-null-island",
x: geo.MakePoint(0, 0),
y: geo.MakePoint(0, 0),
want: 0.0 * geo.Radian,
},
{
name: "same-point-north-pole",
x: geo.MakePoint(+90, 0),
y: geo.MakePoint(+90, +90),
want: 0.0 * geo.Radian,
},
{
name: "same-point-south-pole",
x: geo.MakePoint(-90, 0),
y: geo.MakePoint(-90, -90),
want: 0.0 * geo.Radian,
},
{
name: "north-pole-to-south-pole",
x: geo.MakePoint(+90, 0),
y: geo.MakePoint(-90, -90),
want: math.Pi * geo.Radian,
},
{
name: "toronto-to-montreal",
x: geo.MakePoint(+43.6532, -79.3832),
y: geo.MakePoint(+45.5019, -73.5674),
want: 504.26 * kmToRad * geo.Radian,
},
{
name: "sydney-to-san-francisco",
x: geo.MakePoint(-33.8727, +151.2057),
y: geo.MakePoint(+37.7749, -122.4194),
want: 11948.18 * kmToRad * geo.Radian,
},
{
name: "new-york-to-paris",
x: geo.MakePoint(+40.7128, -74.0060),
y: geo.MakePoint(+48.8575, +2.3514),
want: 5837.15 * kmToRad * geo.Radian,
},
{
name: "seattle-to-tokyo",
x: geo.MakePoint(+47.6061, -122.3328),
y: geo.MakePoint(+35.6764, +139.6500),
want: 7700.00 * kmToRad * geo.Radian,
},
{
// Subtle floating point imprecision can propagate and lead to
// trigonometric functions receiving inputs outside their
// domain, thus returning NaN.
// Test one such case.
name: "floating-point-precision-test",
x: geo.MakePoint(-6.0, 0.0),
y: geo.MakePoint(-6.0, 0.0),
want: 0.0 * geo.Radian,
},
}
func TestPointSphericalAngleTo(t *testing.T) {
const earthRadius = 6371.000 // volumetric mean radius (km)
const kmToRad = 1 / earthRadius
for _, tt := range []struct {
name string
x geo.Point
y geo.Point
want geo.Radians
wantErr string
}{
{
name: "same-point-null-island",
x: geo.MakePoint(0, 0),
y: geo.MakePoint(0, 0),
want: 0.0 * geo.Radian,
},
{
name: "same-point-north-pole",
x: geo.MakePoint(+90, 0),
y: geo.MakePoint(+90, +90),
want: 0.0 * geo.Radian,
},
{
name: "same-point-south-pole",
x: geo.MakePoint(-90, 0),
y: geo.MakePoint(-90, -90),
want: 0.0 * geo.Radian,
},
{
name: "north-pole-to-south-pole",
x: geo.MakePoint(+90, 0),
y: geo.MakePoint(-90, -90),
want: math.Pi * geo.Radian,
},
{
name: "toronto-to-montreal",
x: geo.MakePoint(+43.6532, -79.3832),
y: geo.MakePoint(+45.5019, -73.5674),
want: 504.26 * kmToRad * geo.Radian,
},
{
name: "sydney-to-san-francisco",
x: geo.MakePoint(-33.8727, +151.2057),
y: geo.MakePoint(+37.7749, -122.4194),
want: 11948.18 * kmToRad * geo.Radian,
},
{
name: "new-york-to-paris",
x: geo.MakePoint(+40.7128, -74.0060),
y: geo.MakePoint(+48.8575, +2.3514),
want: 5837.15 * kmToRad * geo.Radian,
},
{
name: "seattle-to-tokyo",
x: geo.MakePoint(+47.6061, -122.3328),
y: geo.MakePoint(+35.6764, +139.6500),
want: 7700.00 * kmToRad * geo.Radian,
},
} {
for _, tt := range corpusPointSphericalAngleTo {
t.Run(tt.name, func(t *testing.T) {
got, err := tt.x.SphericalAngleTo(tt.y)
if tt.wantErr == "" && err != nil {
@@ -536,6 +550,23 @@ func TestPointSphericalAngleTo(t *testing.T) {
}
}
func FuzzPointSphericalAngleTo(f *testing.F) {
for _, tt := range corpusPointSphericalAngleTo {
xLat, xLng, _ := tt.x.LatLngFloat64()
yLat, yLng, _ := tt.y.LatLngFloat64()
f.Add(xLat, xLng, yLat, yLng)
}
f.Fuzz(func(t *testing.T, xLat float64, xLng float64, yLat float64, yLng float64) {
x := geo.MakePoint(geo.Degrees(xLat), geo.Degrees(xLng))
y := geo.MakePoint(geo.Degrees(yLat), geo.Degrees(yLng))
got, _ := x.SphericalAngleTo(y)
if math.IsNaN(float64(got)) {
t.Errorf("got NaN result with xLat=%.15f xLng=%.15f yLat=%.15f yLng=%.15f", xLat, xLng, yLat, yLng)
}
})
}
func approx[T ~float64](x, y T) bool {
return math.Abs(float64(x)-float64(y)) <= 1e-5
}