From 7319ad6a0ba2f8a6450d777530f9aa6248699515 Mon Sep 17 00:00:00 2001
From: Linas Medziunas <linas.medziunas@gmail.com>
Date: Fri, 8 Dec 2023 10:59:00 +0200
Subject: [PATCH] promql: simplify Native Histogram arithmetics

Signed-off-by: Linas Medziunas <linas.medziunas@gmail.com>
---
 promql/engine.go    | 33 +++++----------------------------
 promql/functions.go | 19 +++----------------
 2 files changed, 8 insertions(+), 44 deletions(-)

diff --git a/promql/engine.go b/promql/engine.go
index 4fa2a513b..4e0900686 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -2478,22 +2478,12 @@ func vectorElemBinop(op parser.ItemType, lhs, rhs float64, hlhs, hrhs *histogram
 	switch op {
 	case parser.ADD:
 		if hlhs != nil && hrhs != nil {
-			// The histogram being added must have the larger schema
-			// code (i.e. the higher resolution).
-			if hrhs.Schema >= hlhs.Schema {
-				return 0, hlhs.Copy().Add(hrhs).Compact(0), true
-			}
-			return 0, hrhs.Copy().Add(hlhs).Compact(0), true
+			return 0, hlhs.Copy().Add(hrhs).Compact(0), true
 		}
 		return lhs + rhs, nil, true
 	case parser.SUB:
 		if hlhs != nil && hrhs != nil {
-			// The histogram being subtracted must have the larger schema
-			// code (i.e. the higher resolution).
-			if hrhs.Schema >= hlhs.Schema {
-				return 0, hlhs.Copy().Sub(hrhs).Compact(0), true
-			}
-			return 0, hrhs.Copy().Mul(-1).Add(hlhs).Compact(0), true
+			return 0, hlhs.Copy().Sub(hrhs).Compact(0), true
 		}
 		return lhs - rhs, nil, true
 	case parser.MUL:
@@ -2678,13 +2668,7 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, grouping []string, par
 			if s.H != nil {
 				group.hasHistogram = true
 				if group.histogramValue != nil {
-					// The histogram being added must have
-					// an equal or larger schema.
-					if s.H.Schema >= group.histogramValue.Schema {
-						group.histogramValue.Add(s.H)
-					} else {
-						group.histogramValue = s.H.Copy().Add(group.histogramValue)
-					}
+					group.histogramValue.Add(s.H)
 				}
 				// Otherwise the aggregation contained floats
 				// previously and will be invalid anyway. No
@@ -2701,15 +2685,8 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, grouping []string, par
 				if group.histogramMean != nil {
 					left := s.H.Copy().Div(float64(group.groupCount))
 					right := group.histogramMean.Copy().Div(float64(group.groupCount))
-					// The histogram being added/subtracted must have
-					// an equal or larger schema.
-					if s.H.Schema >= group.histogramMean.Schema {
-						toAdd := right.Mul(-1).Add(left)
-						group.histogramMean.Add(toAdd)
-					} else {
-						toAdd := left.Sub(right)
-						group.histogramMean = toAdd.Add(group.histogramMean)
-					}
+					toAdd := left.Sub(right)
+					group.histogramMean.Add(toAdd)
 				}
 				// Otherwise the aggregation contained floats
 				// previously and will be invalid anyway. No
diff --git a/promql/functions.go b/promql/functions.go
index 06f6f8c71..64066edbb 100644
--- a/promql/functions.go
+++ b/promql/functions.go
@@ -532,15 +532,8 @@ func funcAvgOverTime(vals []parser.Value, args parser.Expressions, enh *EvalNode
 				count++
 				left := h.H.Copy().Div(float64(count))
 				right := mean.Copy().Div(float64(count))
-				// The histogram being added/subtracted must have
-				// an equal or larger schema.
-				if h.H.Schema >= mean.Schema {
-					toAdd := right.Mul(-1).Add(left)
-					mean.Add(toAdd)
-				} else {
-					toAdd := left.Sub(right)
-					mean = toAdd.Add(mean)
-				}
+				toAdd := left.Sub(right)
+				mean.Add(toAdd)
 			}
 			return mean
 		}), nil
@@ -661,13 +654,7 @@ func funcSumOverTime(vals []parser.Value, args parser.Expressions, enh *EvalNode
 		return aggrHistOverTime(vals, enh, func(s Series) *histogram.FloatHistogram {
 			sum := s.Histograms[0].H.Copy()
 			for _, h := range s.Histograms[1:] {
-				// The histogram being added must have
-				// an equal or larger schema.
-				if h.H.Schema >= sum.Schema {
-					sum.Add(h.H)
-				} else {
-					sum = h.H.Copy().Add(sum)
-				}
+				sum.Add(h.H)
 			}
 			return sum
 		}), nil