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hash_to_point(): Introduce final_piece boolean flag 

This toggles the assignment of q_s2 on the last row of each piece.
We assign q_s2 = 2 on the last row of the final piece, and q_s2 = 0
on the last row of other pieces.

This allows us to process the final_piece in the main loop together
with the other pieces.

Co-authored-by: Jack Grigg <jack@electriccoin.co>
This commit is contained in:
therealyingtong 2021-06-20 10:55:26 +08:00
parent 031bb0bc87
commit 9ce29d9d4d
1 changed files with 24 additions and 28 deletions
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52
src/circuit/gadget/sinsemilla/chip/hash_to_point.rs
View File

@ -60,10 +60,12 @@ impl SinsemillaChip {
let mut zs_sum: Vec<Vec<CellValue<pallas::Base>>> = Vec::new();
// Hash each piece in the message except the final piece.
for piece in message[0..(message.len() - 1)].iter() {
// Hash each piece in the message.
for (idx, piece) in message[0..message.len()].iter().enumerate() {
let final_piece = idx == message.len() - 1;
// The value of the accumulator after this piece is processed.
let (x, y, zs) = self.hash_piece(region, offset, piece, x_a, y_a)?;
let (x, y, zs) = self.hash_piece(region, offset, piece, x_a, y_a, final_piece)?;
// Since each message word takes one row to process, we increase
// the offset by `piece.num_words` on each iteration.
@ -75,29 +77,9 @@ impl SinsemillaChip {
zs_sum.push(zs);
}
// Hash the final message piece.
// Assign the final y_a.
let y_a = {
let piece = &message[message.len() - 1];
// The value of the accumulator after this piece is processed.
let (x, y, zs) = self.hash_piece(region, offset, piece, x_a, y_a)?;
// Since each message word takes one row to process, we increase
// the offset by `piece.num_words` on each iteration.
offset += piece.num_words();
// Update the accumulator to the latest value.
x_a = x;
y_a = y;
zs_sum.push(zs);
// Assign and constrain the final `y_a`.
region.assign_fixed(
|| "qs_2 = 2 on final row",
config.q_sinsemilla2,
offset - 1,
|| Ok(pallas::Base::from_u64(2)),
)?;
// Assign the final y_a.
let y_a_cell = region.assign_advice(
|| "y_a",
config.lambda_1,
@ -181,6 +163,7 @@ impl SinsemillaChip {
>>::MessagePiece,
x_a: X<pallas::Base>,
y_a: Y<pallas::Base>,
final_piece: bool,
) -> Result<
(
X<pallas::Base>,
@ -208,12 +191,25 @@ impl SinsemillaChip {
)?;
}
// Set `q_sinsemilla2` fixed column to 0 on the last row.
// Set `q_sinsemilla2` fixed column to 0 on the last row if this is
// not the final piece, or to 2 on the last row of the final piece.
region.assign_fixed(
|| "q_s2 = 1",
|| {
if final_piece {
"q_s2 for final piece"
} else {
"q_s2 between pieces"
}
},
config.q_sinsemilla2,
offset + piece.num_words() - 1,
|| Ok(pallas::Base::zero()),
|| {
Ok(if final_piece {
pallas::Base::from_u64(2)
} else {
pallas::Base::zero()
})
},
)?;
}