Fix float64 comparison test failure on archs using FMA

prometheus/histogram_test.go

@@ -355,13 +355,12 @@ 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 tolerance = 0.0001
+	if !equalFloat64s(got, want, 0.0001) {
+		t.Errorf("exponential buckets range: got %v, want %v (tolerance %f)", got, want, tolerance)
 	}
 }
 
@@ -467,3 +466,23 @@ func TestHistogramExemplar(t *testing.T) {
 		}
 	}
 }
+
+// equalFloat64 returns true if a and b are within the tolerance. We have this
+// because float comparison varies on different architectures. For example,
+// architectures which do FMA yield slightly different results.
+// https://github.com/prometheus/client_golang/pull/899#issuecomment-1244506390
+func equalFloat64(a, b, tolerance float64) bool {
+	return math.Abs(a-b) < tolerance
+}
+
+func equalFloat64s(a, b []float64, tolerance float64) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if !equalFloat64(a[i], b[i], tolerance) {
+			return false
+		}
+	}
+	return true
+}