Better NaN handling for fastMin and fastMax

geom/util.go

@@ -2,6 +2,7 @@ package geom
 
 import (
 	"fmt"
+	"math"
 	"sort"
 )
 
@@ -69,15 +70,15 @@ func sequenceToXYs(seq Sequence) []XY {
 
 // fastMin is a faster but not functionally identical version of math.Min.
 func fastMin(a, b float64) float64 {
-	if a < b {
+	if math.IsNaN(a) || a < b {
 		return a
 	}
 	return b
 }
 
 // fastMax is a faster but not functionally identical version of math.Max.
 func fastMax(a, b float64) float64 {
-	if a > b {
+	if math.IsNaN(a) || a > b {
 		return a
 	}
 	return b

geom/util_internal_test.go

@@ -0,0 +1,71 @@
+package geom
+
+import (
+	"math"
+	"strconv"
+	"testing"
+)
+
+func TestFastMinFastMax(t *testing.T) {
+	var (
+		nan = math.NaN()
+		inf = math.Inf(1)
+		eq  = func(a, b float64) bool {
+			return (math.IsNaN(a) && math.IsNaN(b)) || a == b
+		}
+	)
+	for i, tc := range []struct {
+		a, b     float64
+		min, max float64
+	}{
+		{0, 0, 0, 0},
+		{1, 2, 1, 2},
+		{2, 1, 1, 2},
+		{0, nan, nan, nan},
+		{nan, 0, nan, nan},
+		{nan, nan, nan, nan},
+		{0, inf, 0, inf},
+		{inf, 0, 0, inf},
+		{inf, inf, inf, inf},
+		{0, -inf, -inf, 0},
+		{-inf, 0, -inf, 0},
+		{-inf, -inf, -inf, -inf},
+	} {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			gotMin := fastMin(tc.a, tc.b)
+			gotMax := fastMax(tc.a, tc.b)
+			if !eq(gotMin, tc.min) {
+				t.Errorf("fastMin(%v, %v) = %v, want %v", tc.a, tc.b, gotMin, tc.min)
+			}
+			if !eq(gotMax, tc.max) {
+				t.Errorf("fastMax(%v, %v) = %v, want %v", tc.a, tc.b, gotMax, tc.max)
+			}
+		})
+	}
+}
+
+var global float64
+
+func BenchmarkFastMin(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		global = fastMin(global, 2)
+	}
+}
+
+func BenchmarkFastMax(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		global = fastMax(global, 2)
+	}
+}
+
+func BenchmarkMathMin(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		global = math.Min(global, 2)
+	}
+}
+
+func BenchmarkMathMax(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		global = math.Max(global, 2)
+	}
+}