Add common ammounts commitment lookup table

Author: SyntheticBird45

constants/Cargo.toml

@@ -13,10 +13,11 @@ default = []
 block   = []
 build   = []
 rpc     = []
+crypto  = []
 
 [dependencies]
 
 [dev-dependencies]
 
 [lints]
-workspace = true
+workspace = true

constants/src/crypto.rs

@@ -8,5 +8,7 @@ mod macros;
 pub mod block;
 #[cfg(feature = "build")]
 pub mod build;
+#[cfg(feature = "crypto")]
+pub mod crypto;
 #[cfg(feature = "rpc")]
 pub mod rpc;

constants/src/lib.rs

@@ -18,6 +18,7 @@ redb-memory = ["cuprate-database/redb-memory"]
 service     = ["dep:thread_local", "dep:rayon", "cuprate-helper/thread"]
 
 [dependencies]
+cuprate-constants        = { path = "../../constants", features = ["crypto"]}
 cuprate-database         = { path = "../database" }
 cuprate-database-service = { path = "../service" }
 cuprate-helper           = { path = "../../helper", features = ["fs", "map"] }
@@ -37,7 +38,6 @@ thread_local = { workspace = true, optional = true }
 rayon        = { workspace = true, optional = true }
 
 [dev-dependencies]
-cuprate-constants  = { path = "../../constants" }
 cuprate-helper     = { path = "../../helper", features = ["thread", "cast"] }
 cuprate-test-utils = { path = "../../test-utils" }
 

storage/blockchain/Cargo.toml

@@ -1,9 +1,12 @@
 //! Output functions.
 
 //---------------------------------------------------------------------------------------------------- Import
-use curve25519_dalek::{constants::ED25519_BASEPOINT_POINT, edwards::CompressedEdwardsY, Scalar};
+use curve25519_dalek::{
+    constants::ED25519_BASEPOINT_POINT, edwards::CompressedEdwardsY, EdwardsPoint, Scalar,
+};
 use monero_serai::{generators::H, transaction::Timelock};
 
+use cuprate_constants::crypto::ZERO_COMMITMENT_LOOKUP_TABLE as ZC_LT;
 use cuprate_database::{
     RuntimeError, {DatabaseRo, DatabaseRw},
 };
@@ -155,9 +158,31 @@ pub fn output_to_output_on_chain(
     amount: Amount,
     table_tx_unlock_time: &impl DatabaseRo<TxUnlockTime>,
 ) -> Result<OutputOnChain, RuntimeError> {
-    // FIXME: implement lookup table for common values:
-    // <https://github.com/monero-project/monero/blob/c8214782fb2a769c57382a999eaf099691c836e7/src/ringct/rctOps.cpp#L322>
-    let commitment = ED25519_BASEPOINT_POINT + *H * Scalar::from(amount);
+    // Binary search in lookup table (O(log2(n)+2) instead of O(n+2))
+    let commitment: EdwardsPoint = {
+        let (mut start, mut end, mut c): (usize, usize, Option<EdwardsPoint>) =
+            (0, (ZC_LT.len() - 1) / 2, None);
+        while start <= end {
+            let mid = (start + end) / 2;
+            let lookup = ZC_LT[mid].0;
+            match amount {
+                a if a == lookup => {
+                    c = CompressedEdwardsY::from_slice(&ZC_LT[mid].1)
+                        .expect("The lookup table cannot contain invalid curve point data")
+                        .decompress();
+                }
+                a if a < lookup => {
+                    end = mid - 1;
+                }
+                _ => {
+                    start = mid + 1;
+                }
+            }
+        }
+
+        // Compute the zero commitment if not found.
+        c.unwrap_or_else(|| ED25519_BASEPOINT_POINT + *H * Scalar::from(amount))
+    };
 
     let time_lock = if output
         .output_flags

storage/blockchain/src/ops/output.rs

@@ -2,9 +2,12 @@
 
 //---------------------------------------------------------------------------------------------------- Import
 use bytemuck::TransparentWrapper;
-use curve25519_dalek::{constants::ED25519_BASEPOINT_POINT, Scalar};
+use curve25519_dalek::{
+    constants::ED25519_BASEPOINT_POINT, edwards::CompressedEdwardsY, EdwardsPoint, Scalar,
+};
 use monero_serai::transaction::{Input, Timelock, Transaction};
 
+use cuprate_constants::crypto::ZERO_COMMITMENT_LOOKUP_TABLE as ZC_LT;
 use cuprate_database::{DatabaseRo, DatabaseRw, RuntimeError, StorableVec};
 
 use crate::{
@@ -136,18 +139,49 @@ pub fn add_tx(
             .enumerate()
             .map(|(i, output)| {
                 // Create commitment.
-                // <https://github.com/Cuprate/cuprate/pull/102#discussion_r1559489302>
-                // FIXME: implement lookup table for common values:
-                // <https://github.com/monero-project/monero/blob/c8214782fb2a769c57382a999eaf099691c836e7/src/ringct/rctOps.cpp#L322>
-                let commitment = if miner_tx {
-                    ED25519_BASEPOINT_POINT
-                        + *monero_serai::generators::H * Scalar::from(output.amount.unwrap_or(0))
-                } else {
-                    proofs
-                        .as_ref()
-                        .expect("A V2 transaction with no RCT proofs is a miner tx")
-                        .base
-                        .commitments[i]
+
+                // Binary search in lookup table (O(log2(n)+2) instead of O(n+2))
+                let commitment: EdwardsPoint = {
+                    let (mut start, mut end, mut c, amount): (
+                        usize,
+                        usize,
+                        Option<EdwardsPoint>,
+                        u64,
+                    ) = (0, (ZC_LT.len() - 1) / 2, None, output.amount.unwrap_or(0));
+                    while start <= end {
+                        let mid = (start + end) / 2;
+                        let lookup = ZC_LT[mid].0;
+                        match amount {
+                            a if a == lookup => {
+                                c = CompressedEdwardsY::from_slice(&ZC_LT[mid].1)
+                                    .expect(
+                                        "The lookup table cannot contain invalid curve point data",
+                                    )
+                                    .decompress();
+                            }
+                            a if a < lookup => {
+                                end = mid - 1;
+                            }
+                            _ => {
+                                start = mid + 1;
+                            }
+                        }
+                    }
+
+                    // Compute commitment if not found.
+                    c.unwrap_or_else(|| {
+                        if miner_tx {
+                            ED25519_BASEPOINT_POINT
+                                + *monero_serai::generators::H
+                                    * Scalar::from(output.amount.unwrap_or(0))
+                        } else {
+                            proofs
+                                .as_ref()
+                                .expect("A V2 transaction with no RCT proofs is a miner tx")
+                                .base
+                                .commitments[i]
+                        }
+                    })
                 };
 
                 // Add the RCT output.