From 227fd15b965bdf5b47724df57eeaf6935587fdd9 Mon Sep 17 00:00:00 2001
From: Ryan Goodfellow <ryan.goodfellow@oxide.computer>
Date: Tue, 21 May 2024 21:29:16 -0700
Subject: [PATCH] fix deparse for non-aligned fields > 8 bits (#49)

---
 codegen/rust/src/header.rs | 19 +++++++------------
 test/src/vlan.rs           | 10 ++++++++--
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/codegen/rust/src/header.rs b/codegen/rust/src/header.rs
index 448de5b0..b5b1b84d 100644
--- a/codegen/rust/src/header.rs
+++ b/codegen/rust/src/header.rs
@@ -85,21 +85,16 @@ impl<'a> HeaderGenerator<'a> {
                 // NOTE this barfing and then unbarfing a vec is to handle
                 // the p4 confused-endian data model.
                 let mut v = self.#name.clone().into_vec();
+                if ((#end-#offset) % 8) != 0 {
+                    if let Some(x) = v.iter_mut().last() {
+                        *x >>= ((#end - #offset) % 8);
+                    }
+                }
                 v.reverse();
                 let n = (#end-#offset);
                 let m = n%8;
-                if (n > 8) && m != 0 {
-                    let mut b = BitVec::<u8, Msb0>::from_vec(v);
-                    if b.len() > m {
-                        x[#offset..#end] |= &b[m..];
-                    } else {
-                        x[#offset..#end] |= &b;
-                    }
-                } else {
-                    let mut b = BitVec::<u8, Msb0>::from_vec(v);
-                    b.resize(#end-#offset, false);
-                    x[#offset..#end] |= &b;
-                }
+                let mut b = BitVec::<u8, Msb0>::from_vec(v);
+                x[#offset..#end] |= &b[m..];
 
             });
             checksum_statements.push(quote! {
diff --git a/test/src/vlan.rs b/test/src/vlan.rs
index b804b9fc..8e42e867 100644
--- a/test/src/vlan.rs
+++ b/test/src/vlan.rs
@@ -2,21 +2,27 @@ p4_macro::use_p4!("test/src/p4/vlan_header.p4");
 
 #[test]
 fn test_vlan_parse() -> anyhow::Result<()> {
-    let mut data = [0u8; 256];
+    let mut data = [0u8; 4];
     data[0] = 0x0;
     data[1] = 0x47;
     let mut pkt = vlan_h::new();
     pkt.set(&data).unwrap();
     let vid: u16 = pkt.vid.to_owned().load_le();
     assert_eq!(vid, 0x47);
+    let bv = pkt.to_bitvec();
+    let readback = bv.into_vec();
+    assert_eq!(data.to_vec(), readback);
 
-    let mut data = [0u8; 256];
+    let mut data = [0u8; 4];
     data[0] = 0x77;
     data[1] = 0x47;
     let mut pkt = vlan_h::new();
     pkt.set(&data).unwrap();
     let vid: u16 = pkt.vid.to_owned().load_le();
     assert_eq!(vid, 0x747);
+    let bv = pkt.to_bitvec();
+    let readback = bv.into_vec();
+    assert_eq!(data.to_vec(), readback);
 
     Ok(())
 }