From bd08808566b5fbeae9b89f0ae00157afee01e617 Mon Sep 17 00:00:00 2001
From: therealyingtong <yingtong@z.cash>
Date: Sun, 20 Jun 2021 20:54:33 +0800
Subject: [PATCH] SinsemillaChip::configure(): Merge "Initial y_q" gate with
 main gate

This allows the MockProver to see the fixed_y_q query as semantically
connected to q_sinsemilla1.

Co-authored-by: Jack Grigg <jack@electriccoin.co>
---
 src/circuit/gadget/sinsemilla/chip.rs          | 17 ++++++-----------
 .../gadget/sinsemilla/chip/hash_to_point.rs    | 18 +++++++++++++++---
 2 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/src/circuit/gadget/sinsemilla/chip.rs b/src/circuit/gadget/sinsemilla/chip.rs
index 2612bfe4..2549a384 100644
--- a/src/circuit/gadget/sinsemilla/chip.rs
+++ b/src/circuit/gadget/sinsemilla/chip.rs
@@ -150,17 +150,6 @@ impl SinsemillaChip {
             (lambda_1 + lambda_2) * (x_a - x_r(meta, rotation))
         };
 
-        // Check that the initial x_A, x_P, lambda_1, lambda_2 are consistent with y_Q.
-        meta.create_gate("Initial y_Q", |meta| {
-            let fixed_y_q = meta.query_fixed(config.fixed_y_q, Rotation::cur());
-
-            // Y_A = (lambda_1 + lambda_2) * (x_a - x_r)
-            let Y_A = Y_A(meta, Rotation::cur());
-
-            // fixed_y_q * (2 * fixed_y_q - Y_{A,0}) = 0
-            vec![fixed_y_q.clone() * (two.clone() * fixed_y_q - Y_A)]
-        });
-
         meta.create_gate("Sinsemilla gate", |meta| {
             let q_s1 = meta.query_selector(config.q_sinsemilla1);
             let q_s2 = meta.query_fixed(config.q_sinsemilla2, Rotation::cur());
@@ -168,6 +157,7 @@ impl SinsemillaChip {
                 let one = Expression::Constant(pallas::Base::one());
                 q_s2.clone() * (q_s2 - one)
             };
+            let fixed_y_q = meta.query_fixed(config.fixed_y_q, Rotation::cur());
 
             let lambda_1_next = meta.query_advice(config.lambda_1, Rotation::next());
             let lambda_2_cur = meta.query_advice(config.lambda_2, Rotation::cur());
@@ -183,6 +173,10 @@ impl SinsemillaChip {
             // Y_A = (lambda_1 + lambda_2) * (x_a - x_r)
             let Y_A_next = Y_A(meta, Rotation::next());
 
+            // Check that the initial x_A, x_P, lambda_1, lambda_2 are consistent with y_Q.
+            // fixed_y_q * (2 * fixed_y_q - Y_{A,0}) = 0
+            let init_y_q_check = fixed_y_q.clone() * (two.clone() * fixed_y_q - Y_A_cur.clone());
+
             // lambda2^2 - (x_a_next + x_r + x_a_cur) = 0
             let secant_line =
                 lambda_2_cur.clone().square() - (x_a_next.clone() + x_r + x_a_cur.clone());
@@ -207,6 +201,7 @@ impl SinsemillaChip {
             };
 
             vec![
+                ("Initial y_q", init_y_q_check),
                 ("Secant line", q_s1.clone() * secant_line),
                 ("Sinsemilla gate", q_s1 * expr),
             ]
diff --git a/src/circuit/gadget/sinsemilla/chip/hash_to_point.rs b/src/circuit/gadget/sinsemilla/chip/hash_to_point.rs
index 7bc24031..c72e503e 100644
--- a/src/circuit/gadget/sinsemilla/chip/hash_to_point.rs
+++ b/src/circuit/gadget/sinsemilla/chip/hash_to_point.rs
@@ -57,8 +57,20 @@ impl SinsemillaChip {
             )?;
 
             // Constrain the initial x_a, lambda_1, lambda_2, x_p using the fixed y_q
-            // initializer.
-            region.assign_fixed(|| "fixed y_q", config.fixed_y_q, offset, || Ok(y_q))?;
+            // initializer. Assign `fixed_y_q` to be zero on every other row.
+            {
+                region.assign_fixed(|| "fixed y_q", config.fixed_y_q, offset, || Ok(y_q))?;
+
+                let total_num_words = message.iter().map(|piece| piece.num_words()).sum();
+                for row in 1..total_num_words {
+                    region.assign_fixed(
+                        || "fixed y_q",
+                        config.fixed_y_q,
+                        offset + row,
+                        || Ok(pallas::Base::zero()),
+                    )?;
+                }
+            }
 
             let y_a = Some(y_q);
 
@@ -68,7 +80,7 @@ impl SinsemillaChip {
         let mut zs_sum: Vec<Vec<CellValue<pallas::Base>>> = Vec::new();
 
         // Hash each piece in the message.
-        for (idx, piece) in message[0..message.len()].iter().enumerate() {
+        for (idx, piece) in message.iter().enumerate() {
             let final_piece = idx == message.len() - 1;
 
             // The value of the accumulator after this piece is processed.