Fix bundle::Action to hold cmx instead of cm

src/bundle.rs

@@ -4,7 +4,7 @@ use nonempty::NonEmpty;
 
 use crate::{
     circuit::Proof,
-    note::{EncryptedNote, NoteCommitment, Nullifier},
+    note::{EncryptedNote, ExtractedNoteCommitment, Nullifier},
     primitives::redpallas::{self, Binding, SpendAuth},
     tree::Anchor,
     value::{ValueCommitment, ValueSum},
@@ -25,7 +25,7 @@ pub struct Action<T> {
     /// The randomized verification key for the note being spent.
     rk: redpallas::VerificationKey<SpendAuth>,
     /// A commitment to the new note being created.
-    cm_new: NoteCommitment,
+    cm_new: ExtractedNoteCommitment,
     /// The encrypted output note.
     encrypted_note: EncryptedNote,
     /// A commitment to the net value created or consumed by this action.

src/note.rs

@@ -9,7 +9,7 @@ use crate::{
 };
 
 mod commitment;
-pub use self::commitment::NoteCommitment;
+pub use self::commitment::{ExtractedNoteCommitment, NoteCommitment};
 
 mod nullifier;
 pub use self::nullifier::Nullifier;

src/note/commitment.rs

@@ -8,7 +8,7 @@ use subtle::CtOption;
 use crate::{
     constants::L_ORCHARD_BASE,
     primitives::sinsemilla,
-    spec::{prf_expand, to_scalar},
+    spec::{extract_p, prf_expand, to_scalar},
     value::NoteValue,
 };
 
@@ -54,3 +54,13 @@ impl NoteCommitment {
             .map(NoteCommitment)
     }
 }
+
+/// The x-coordinate of the commitment to a note.
+#[derive(Debug)]
+pub struct ExtractedNoteCommitment(pub(super) pallas::Base);
+
+impl From<NoteCommitment> for ExtractedNoteCommitment {
+    fn from(cm: NoteCommitment) -> Self {
+        ExtractedNoteCommitment(extract_p(&cm.0))
+    }
+}