fix: preserve sign bit during signed integer encoding (fixes #6)

templates/signed.txt

@@ -26,11 +26,23 @@ impl Element for {{ name }} {
         let bytes = self.0.to_be_bytes();
         if self.0 >= 0 {
             let first_non_zero = bytes.iter().position(|&b| b != 0).unwrap_or(bytes.len() - 1);
-            buf.put_slice(&bytes[first_non_zero..]);
+            // Preserve sign: if the leading byte has bit 7 set, keep the 0x00 before it
+            let start = if first_non_zero > 0 && bytes[first_non_zero] & 0x80 != 0 {
+                first_non_zero - 1
+            } else {
+                first_non_zero
+            };
+            buf.put_slice(&bytes[start..]);
             Ok(())
         } else {
             let first_non_ff = bytes.iter().position(|&b| b != 0xFF).unwrap_or(bytes.len() - 1);
-            buf.put_slice(&bytes[first_non_ff..]);
+            // Preserve sign: if the leading byte has bit 7 clear, keep the 0xFF before it
+            let start = if first_non_ff > 0 && bytes[first_non_ff] & 0x80 == 0 {
+                first_non_ff - 1
+            } else {
+                first_non_ff
+            };
+            buf.put_slice(&bytes[start..]);
             Ok(())
         }
     }

tests/ebml.rs

@@ -43,6 +43,25 @@ fn write_ebml() {
     assert_eq!(ebml, ebml_read);
 }
 
+#[test]
+fn test_signed_integer_preserve_sign_bit() {
+    // Encode
+    let dp = DiscardPadding(14833333_i64);
+    let mut buf = Vec::new();
+    dp.encode_body(&mut buf).unwrap();
+    // Decode
+    let mut b: &[u8] = &buf[..];
+    let decoded = DiscardPadding::decode_body(&mut b).unwrap();
+    assert_eq!(dp, decoded);
+    // Also test negative for regressions
+    let dp_neg = DiscardPadding(-14833333_i64);
+    let mut buf_neg = Vec::new();
+    dp_neg.encode_body(&mut buf_neg).unwrap();
+    let mut b_neg: &[u8] = &buf_neg[..];
+    let decoded_neg = DiscardPadding::decode_body(&mut b_neg).unwrap();
+    assert_eq!(dp_neg, decoded_neg);
+}
+
 #[cfg(feature = "tokio")]
 mod tokio_tests {
     use mkv_element::io::tokio_impl::*;