From feea06fc3509550ee5b6faf866ae04a8592eecdc Mon Sep 17 00:00:00 2001
From: Erick Ahmed <engineering@erickahmed.com>
Date: Mon, 13 Jul 2026 18:43:57 +0200
Subject: [PATCH] Improve tactic for J1939 metadata parsing on proprietary
 frames

---
 decoder.py | 41 ++++++++++++++++++++++-------------------
 1 file changed, 22 insertions(+), 19 deletions(-)

diff --git a/decoder.py b/decoder.py
index f47397c..47f850d 100644
--- a/decoder.py
+++ b/decoder.py
@@ -14,17 +14,14 @@ def decode_j1939_metadata(lf: pl.LazyFrame) -> pl.LazyFrame:
     """
     id_int = pl.col("ID").str.to_integer(base=16).cast(pl.UInt32)
 
-    id_shifted_8 = id_int // 256
-    id_shifted_16 = id_int // 65536
-
     priority = ((id_int // 67108864) % 8).cast(pl.UInt8)
-    pf = (id_shifted_16 % 256).cast(pl.UInt8)
-    ps = (id_shifted_8 % 256).cast(pl.UInt8)
+    pf = ((id_int // 65536) % 256).cast(pl.UInt8)
+    ps = ((id_int // 256) % 256).cast(pl.UInt8)
     sa = (id_int % 256).cast(pl.UInt8)
 
-    da = pl.when(pf < 240).then(ps).otherwise(pl.lit(255, dtype=pl.UInt8))
+    da = pl.when(pf < 240).then(ps).otherwise(pl.lit(255, dtype=pl.UInt8)).cast(pl.UInt8)
 
-    pgn = pl.when(pf < 240).then(id_shifted_8 % 65536).otherwise(id_shifted_8 % 262144).cast(pl.UInt32)
+    pgn = pl.when(pf < 240).then(((id_int // 256) & 0x3FF00)).otherwise(((id_int // 256) & 0x3FFFF)).cast(pl.UInt32)
 
     return lf.with_columns(
         pl.struct([
@@ -42,21 +39,27 @@ def decode_j1939_frames(df: pl.DataFrame) -> pl.DataFrame:
 
     is_j1939 = id_int > 0x7FF
 
-    priority = (id_int // 67108864) % 8
-    pf = (id_int // 65536) % 256
-    ps = (id_int // 256) % 256
-    sa = id_int % 256
-    da = pl.when(pf < 240).then(ps).otherwise(255)
-    pgn = pl.when(pf < 240).then((id_int // 256) % 65536).otherwise((id_int // 256) % 262144)
+    priority = ((id_int // 67108864) % 8).cast(pl.UInt8)
+    pf = ((id_int // 65536) % 256).cast(pl.UInt8)
+    ps = ((id_int // 256) % 256).cast(pl.UInt8)
+    sa = (id_int % 256).cast(pl.UInt8)
+
+    da = pl.when(pf < 240).then(ps).otherwise(pl.lit(255, dtype=pl.UInt8)).cast(pl.UInt8)
+
+    pgn = pl.when(pf < 240).then(
+        ((id_int // 256) & 0x3FF00)
+    ).otherwise(
+        ((id_int // 256) & 0x3FFFF)
+    ).cast(pl.UInt32)
 
     j1939_meta = pl.when(is_j1939).then(
         pl.struct([
-            priority.cast(pl.UInt8).alias("Priority"),
-            pf.cast(pl.UInt8).alias("PF"),
-            ps.cast(pl.UInt8).alias("PS"),
-            sa.cast(pl.UInt8).alias("SA"),
-            da.cast(pl.UInt8).alias("DA"),
-            pgn.cast(pl.UInt32).alias("PGN")
+            priority.alias("Priority"),
+            pf.alias("PF"),
+            ps.alias("PS"),
+            sa.alias("SA"),
+            da.alias("DA"),
+            pgn.alias("PGN")
         ])
     ).otherwise(None)