Update comments, bitwise comparison of float buckets

Signed-off-by: Linas Medziunas <linas.medziunas@gmail.com>

model/histogram/float_histogram.go

@@ -307,7 +307,8 @@ func (h *FloatHistogram) Sub(other *FloatHistogram) *FloatHistogram {
 // Exact match is when there are no new buckets (even empty) and no missing buckets,
 // and all the bucket values match. Spans can have different empty length spans in between,
 // but they must represent the same bucket layout to match.
-// Non-metadata float fields (Sum, Count, ZeroCount) are compared as binary (using math.Float64bits).
+// Sum, Count, and ZeroCount are compared based on their bit patterns because this method
+// is about data equality rather than mathematical equality.
 func (h *FloatHistogram) Equals(h2 *FloatHistogram) bool {
 	if h2 == nil {
 		return false
@@ -327,10 +328,10 @@ func (h *FloatHistogram) Equals(h2 *FloatHistogram) bool {
 		return false
 	}
 
-	if !bucketsMatch(h.PositiveBuckets, h2.PositiveBuckets) {
+	if !floatBucketsMatch(h.PositiveBuckets, h2.PositiveBuckets) {
 		return false
 	}
-	if !bucketsMatch(h.NegativeBuckets, h2.NegativeBuckets) {
+	if !floatBucketsMatch(h.NegativeBuckets, h2.NegativeBuckets) {
 		return false
 	}
 
@@ -1105,3 +1106,15 @@ func addBuckets(
 
 	return spansA, bucketsA
 }
+
+func floatBucketsMatch(b1, b2 []float64) bool {
+	if len(b1) != len(b2) {
+		return false
+	}
+	for i, b := range b1 {
+		if math.Float64bits(b) != math.Float64bits(b2[i]) {
+			return false
+		}
+	}
+	return true
+}

model/histogram/float_histogram_test.go

@@ -2296,11 +2296,13 @@ func TestFloatBucketIteratorTargetSchema(t *testing.T) {
 // cannot be covered by TestHistogramEquals.
 func TestFloatHistogramEquals(t *testing.T) {
 	h1 := FloatHistogram{
-		Schema:        3,
-		Count:         2.2,
-		Sum:           9.7,
-		ZeroThreshold: 0.1,
-		ZeroCount:     1.1,
+		Schema:          3,
+		Count:           2.2,
+		Sum:             9.7,
+		ZeroThreshold:   0.1,
+		ZeroCount:       1.1,
+		PositiveBuckets: []float64{3},
+		NegativeBuckets: []float64{4},
 	}
 
 	equals := func(h1, h2 FloatHistogram) {
@@ -2326,4 +2328,16 @@ func TestFloatHistogramEquals(t *testing.T) {
 	hZeroCountNaN.ZeroCount = math.NaN()
 	notEquals(h1, *hZeroCountNaN)
 	equals(*hZeroCountNaN, *hZeroCountNaN)
+
+	// Positive bucket value is NaN.
+	hPosBucketNaN := h1.Copy()
+	hPosBucketNaN.PositiveBuckets[0] = math.NaN()
+	notEquals(h1, *hPosBucketNaN)
+	equals(*hPosBucketNaN, *hPosBucketNaN)
+
+	// Negative bucket value is NaN.
+	hNegBucketNaN := h1.Copy()
+	hNegBucketNaN.NegativeBuckets[0] = math.NaN()
+	notEquals(h1, *hNegBucketNaN)
+	equals(*hNegBucketNaN, *hNegBucketNaN)
 }

model/histogram/generic.go

@@ -333,18 +333,6 @@ func compactBuckets[IBC InternalBucketCount](buckets []IBC, spans []Span, maxEmp
 	return buckets, spans
 }
 
-func bucketsMatch[IBC InternalBucketCount](b1, b2 []IBC) bool {
-	if len(b1) != len(b2) {
-		return false
-	}
-	for i, b := range b1 {
-		if b != b2[i] {
-			return false
-		}
-	}
-	return true
-}
-
 func getBound(idx, schema int32) float64 {
 	// Here a bit of context about the behavior for the last bucket counting
 	// regular numbers (called simply "last bucket" below) and the bucket

model/histogram/histogram.go

@@ -17,6 +17,8 @@ import (
 	"fmt"
 	"math"
 	"strings"
+
+	"golang.org/x/exp/slices"
 )
 
 // CounterResetHint contains the known information about a counter reset,
@@ -172,7 +174,8 @@ func (h *Histogram) CumulativeBucketIterator() BucketIterator[uint64] {
 // Exact match is when there are no new buckets (even empty) and no missing buckets,
 // and all the bucket values match. Spans can have different empty length spans in between,
 // but they must represent the same bucket layout to match.
-// Non-metadata float field (Sum) is compared as binary (using math.Float64bits).
+// Sum is compared based on its bit pattern because this method
+// is about data equality rather than mathematical equality.
 func (h *Histogram) Equals(h2 *Histogram) bool {
 	if h2 == nil {
 		return false
@@ -191,10 +194,10 @@ func (h *Histogram) Equals(h2 *Histogram) bool {
 		return false
 	}
 
-	if !bucketsMatch(h.PositiveBuckets, h2.PositiveBuckets) {
+	if !slices.Equal(h.PositiveBuckets, h2.PositiveBuckets) {
 		return false
 	}
-	if !bucketsMatch(h.NegativeBuckets, h2.NegativeBuckets) {
+	if !slices.Equal(h.NegativeBuckets, h2.NegativeBuckets) {
 		return false
 	}