From ba1d0aba9aef2f88bfdb05758d4636ec44a3a9b6 Mon Sep 17 00:00:00 2001
From: roundspring2003 <hwilly40159@gmail.com>
Date: Wed, 25 Mar 2026 19:11:22 +0800
Subject: [PATCH] fix: align constrained INTEGER length encoding with decoder

---
 aper_test.go | 40 ++++++++++++++++++++++++++++++++++++++++
 marshal.go   |  2 +-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/aper_test.go b/aper_test.go
index 3b48be2..f6d8a05 100644
--- a/aper_test.go
+++ b/aper_test.go
@@ -581,6 +581,46 @@ func TestStructInteger(t *testing.T) {
 	}
 }
 
+type intMarshalRegressionLargeRange4096To131071 struct {
+	Value int64 `aper:"valueLB:4096,valueUB:131071"`
+}
+
+type intMarshalRegressionLargeRange0To100000 struct {
+	Value int64 `aper:"valueLB:0,valueUB:100000"`
+}
+
+func TestMarshalIntegerLengthRegression(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    interface{}
+		expected []byte
+	}{
+		{
+			name:     "range_4096_131071_value_5000",
+			input:    intMarshalRegressionLargeRange4096To131071{Value: 5000},
+			expected: []byte{0x40, 0x03, 0x88},
+		},
+		{
+			name:     "range_0_100000_value_65535",
+			input:    intMarshalRegressionLargeRange0To100000{Value: 65535},
+			expected: []byte{0x40, 0xFF, 0xFF},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			encoded, err := Marshal(tc.input)
+			assert.NoError(t, err)
+			assert.Equal(t, tc.expected, encoded)
+
+			out := reflect.New(reflect.TypeOf(tc.input))
+			err = Unmarshal(encoded, out.Interface())
+			assert.NoError(t, err)
+			assert.Equal(t, tc.input, out.Elem().Interface())
+		})
+	}
+}
+
 // TEST ENUMERATED
 
 // value is unconstraint
diff --git a/marshal.go b/marshal.go
index 898d01a..e9c1d34 100644
--- a/marshal.go
+++ b/marshal.go
@@ -453,7 +453,7 @@ func (pd *perRawBitData) appendInteger(value int64, extensive bool, lowerBoundPt
 		unsignedValueRange := uint64(valueRange - 1)
 		for byteLen = 1; byteLen <= 127; byteLen++ {
 			unsignedValueRange >>= 8
-			if unsignedValueRange <= 1 {
+			if unsignedValueRange == 0 {
 				break
 			}
 		}