From 57c9db1bc36dbb6432817983c4d3af2aa6090b17 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Mon, 1 Mar 2021 16:46:59 +0200
Subject: [PATCH] properly handle Histogram.Update(1e-9)

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1096
---
 histogram.go      | 2 +-
 histogram_test.go | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/histogram.go b/histogram.go
index ebdd00d..e1a168c 100644
--- a/histogram.go
+++ b/histogram.go
@@ -94,7 +94,7 @@ func (h *Histogram) Update(v float64) {
 		h.upper++
 	} else {
 		idx := uint(bucketIdx)
-		if bucketIdx == float64(idx) {
+		if bucketIdx == float64(idx) && idx > 0 {
 			// Edge case for 10^n values, which must go to the lower bucket
 			// according to Prometheus logic for `le`-based histograms.
 			idx--
diff --git a/histogram_test.go b/histogram_test.go
index 7da4045..dea989b 100644
--- a/histogram_test.go
+++ b/histogram_test.go
@@ -97,6 +97,8 @@ prefix_count 120
 	h.Update(math.Inf(-1))
 	h.Update(math.NaN())
 	h.Update(-123)
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1096
+	h.Update(math.Float64frombits(0x3e112e0be826d695))
 
 	// Make sure the histogram becomes visible in the output of WritePrometheus,
 	// since now it contains values.