Fix float64 comparison test failure on archs using FMA

prometheus/histogram_test.go

@@ -28,6 +28,8 @@ import (
 	"github.com/golang/protobuf/proto"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
+	"github.com/prometheus/client_golang/prometheus/internal"
+
 	dto "github.com/prometheus/client_model/go"
 )
 
@@ -355,13 +357,12 @@ func TestBuckets(t *testing.T) {
 
 	got = ExponentialBucketsRange(1, 100, 10)
 	want = []float64{
-		1.0, 1.6681005372000588, 2.782559402207125,
-		4.641588833612779, 7.742636826811273, 12.915496650148842,
-		21.544346900318846, 35.93813663804629, 59.94842503189414,
-		100.00000000000007,
+		1.0, 1.6681, 2.7825, 4.6415, 7.7426, 12.9154, 21.5443,
+		35.9381, 59.9484, 100.0000,
 	}
-	if !reflect.DeepEqual(got, want) {
-		t.Errorf("exponential buckets range: got %v, want %v", got, want)
+	const epsilon = 0.0001
+	if !internal.AlmostEqualFloat64s(got, want, epsilon) {
+		t.Errorf("exponential buckets range: got %v, want %v (epsilon %f)", got, want, epsilon)
 	}
 }
 

prometheus/internal/difflib.go

@@ -22,6 +22,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"math"
 	"strings"
 )
 
@@ -46,6 +47,97 @@ func calculateRatio(matches, length int) float64 {
 	return 1.0
 }
 
+var (
+	// minNormalFloat64 is the smallest positive normal value of type float64.
+	minNormalFloat64 = math.Float64frombits(0x0010000000000000)
+
+	// minNormalFloat32 is the smallest positive normal value of type float32.
+	minNormalFloat32 = math.Float32frombits(0x00800000)
+)
+
+// AlmostEqualFloat64 returns true if a and b are equal within a relative error
+// of epsilon. See http://floating-point-gui.de/errors/comparison/ for the
+// details of the applied method.
+//
+// This function is copy/paste to avoid a dependency.
+// https://github.com/beorn7/floats
+func AlmostEqualFloat64(a, b, epsilon float64) bool {
+	if a == b {
+		return true
+	}
+	absA := math.Abs(a)
+	absB := math.Abs(b)
+	diff := math.Abs(a - b)
+	if a == 0 || b == 0 || absA+absB < minNormalFloat64 {
+		return diff < epsilon*minNormalFloat64
+	}
+	return diff/math.Min(absA+absB, math.MaxFloat64) < epsilon
+}
+
+// AlmostEqualFloat64s is the slice form of AlmostEqualFloat64.
+func AlmostEqualFloat64s(a, b []float64, epsilon float64) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if !AlmostEqualFloat64(a[i], b[i], epsilon) {
+			return false
+		}
+	}
+	return true
+}
+
+// AlmostEqualFloat32 returns true if a and b are equal within a relative error
+// of epsilon. See http://floating-point-gui.de/errors/comparison/ for the
+// details of the applied method.
+//
+// This function is copy/paste to avoid a dependency.
+// https://github.com/beorn7/floats
+func AlmostEqualFloat32(a, b, epsilon float32) bool {
+	if a == b {
+		return true
+	}
+	absA := AbsFloat32(a)
+	absB := AbsFloat32(b)
+	diff := AbsFloat32(a - b)
+	if a == 0 || b == 0 || absA+absB < minNormalFloat32 {
+		return diff < epsilon*minNormalFloat32
+	}
+	return diff/MinFloat32(absA+absB, math.MaxFloat32) < epsilon
+}
+
+// AlmostEqualFloat32s is the slice form of AlmostEqualFloat32.
+func AlmostEqualFloat32s(a, b []float32, epsilon float32) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if !AlmostEqualFloat32(a[i], b[i], epsilon) {
+			return false
+		}
+	}
+	return true
+}
+
+// AbsFloat32 works like math.Abs, but for float32.
+func AbsFloat32(x float32) float32 {
+	switch {
+	case x < 0:
+		return -x
+	case x == 0:
+		return 0 // return correctly abs(-0)
+	}
+	return x
+}
+
+// MinFloat32 works like math.Min, but for float32.
+func MinFloat32(x, y float32) float32 {
+	if x < y {
+		return x
+	}
+	return y
+}
+
 type Match struct {
 	A    int
 	B    int