From 049cab563b4afa53cdd2528bfd3d24558d1facfa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan-Otto=20Kr=C3=B6pke?= <mail@jkroepke.de>
Date: Wed, 7 Oct 2026 17:58:03 +0200
Subject: [PATCH] mi: fix NewInterval inflating durations of 60s or more
 (#2516)
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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>
---
 internal/mi/types.go      | 16 ++++-----
 internal/mi/types_test.go | 68 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+), 9 deletions(-)
 create mode 100644 internal/mi/types_test.go

diff --git a/internal/mi/types.go b/internal/mi/types.go
index c48b7ed1..1bddf1a1 100644
--- a/internal/mi/types.go
+++ b/internal/mi/types.go
@@ -98,17 +98,15 @@ type Interval struct {
 	Padding3     uint32
 }
 
+// NewInterval converts a duration into an MI_Interval. MI sums the fields,
+// so each field holds only the remainder after the next larger unit.
 func NewInterval(interval time.Duration) *Interval {
-	// Convert the duration to a number of microseconds
-	microseconds := interval.Microseconds()
-
-	// Create a new interval with the microseconds
 	return &Interval{
-		Days:         uint32(microseconds / (24 * 60 * 60 * 1000000)),
-		Hours:        uint32(microseconds / (60 * 60 * 1000000)),
-		Minutes:      uint32(microseconds / (60 * 1000000)),
-		Seconds:      uint32(microseconds / 1000000),
-		Microseconds: uint32(microseconds % 1000000),
+		Days:         uint32(interval / (24 * time.Hour)),
+		Hours:        uint32(interval / time.Hour % 24),
+		Minutes:      uint32(interval / time.Minute % 60),
+		Seconds:      uint32(interval / time.Second % 60),
+		Microseconds: uint32(interval / time.Microsecond % 1000000),
 	}
 }
 
diff --git a/internal/mi/types_test.go b/internal/mi/types_test.go
new file mode 100644
index 00000000..1d812dc8
--- /dev/null
+++ b/internal/mi/types_test.go
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package mi_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/prometheus-community/windows_exporter/internal/mi"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewInterval(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name     string
+		duration time.Duration
+		expected mi.Interval
+	}{
+		{
+			name:     "zero",
+			duration: 0,
+			expected: mi.Interval{},
+		},
+		{
+			name:     "sub-minute",
+			duration: 9*time.Second + 500*time.Millisecond,
+			expected: mi.Interval{Seconds: 9, Microseconds: 500000},
+		},
+		{
+			name:     "over a minute",
+			duration: 90 * time.Second,
+			expected: mi.Interval{Minutes: 1, Seconds: 30},
+		},
+		{
+			name:     "hours minutes seconds",
+			duration: 2*time.Hour + 3*time.Minute + 4*time.Second + 500*time.Millisecond,
+			expected: mi.Interval{Hours: 2, Minutes: 3, Seconds: 4, Microseconds: 500000},
+		},
+		{
+			name:     "over a day",
+			duration: 26 * time.Hour,
+			expected: mi.Interval{Days: 1, Hours: 2},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			require.Equal(t, tc.expected, *mi.NewInterval(tc.duration))
+		})
+	}
+}