chore: add `downtimeProduct` configuration parameter (#138)

* add `downtimeProduct` configuration parameter

* formatting

contracts/Configuration.sol

@@ -24,4 +24,8 @@ struct ProofConfig {
   uint256 timeout; // mark proofs as missing before the timeout (in seconds)
   uint8 downtime; // ignore this much recent blocks for proof requirements
   string zkeyHash; // hash of the zkey file which is linked to the verifier
+  // Ensures the pointer does not remain in downtime for many consecutive
+  // periods. For each period increase, move the pointer `pointerProduct`
+  // blocks. Should be a prime number to ensure there are no cycles.
+  uint8 downtimeProduct;
 }

contracts/FuzzMarketplace.sol

@@ -10,7 +10,7 @@ contract FuzzMarketplace is Marketplace {
     Marketplace(
       MarketplaceConfig(
         CollateralConfig(10, 5, 3, 10),
-        ProofConfig(10, 5, 64, "")
+        ProofConfig(10, 5, 64, "", 67)
       ),
       new TestToken(),
       new TestVerifier()

contracts/Proofs.sol

@@ -69,10 +69,8 @@ abstract contract Proofs is Periods {
    */
   function _getPointer(SlotId id, Period period) internal view returns (uint8) {
     uint256 blockNumber = block.number % 256;
-    // To ensure the pointer does not remain in downtime for many consecutive
-    // periods, for each period increase, move the pointer 67 blocks. We've
-    // chosen a prime number to ensure that we don't get cycles.
-    uint256 periodNumber = (Period.unwrap(period) * 67) % 256;
+    uint256 periodNumber = (Period.unwrap(period) * _config.downtimeProduct) %
+      256;
     uint256 idOffset = uint256(SlotId.unwrap(id)) % 256;
     uint256 pointer = (blockNumber + periodNumber + idOffset) % 256;
     return uint8(pointer);

deploy/marketplace.js

@@ -14,6 +14,7 @@ const CONFIGURATION = {
     // `downtime` needs to be larger than `period` when running hardhat
     // in automine mode, because it can produce a block every second
     downtime: 64,
+    downtimeProduct: 67
   },
 }
 

test/Proofs.test.js

@@ -22,6 +22,7 @@ describe("Proofs", function () {
   const timeout = 5
   const downtime = 64
   const probability = 4 // require a proof roughly once every 4 periods
+  const downtimeProduct = 67
   const { periodOf, periodEnd } = periodic(period)
 
   let proofs
@@ -33,7 +34,7 @@ describe("Proofs", function () {
     await deployments.fixture(["Verifier"])
     const verifier = await deployments.get("Groth16Verifier")
     proofs = await Proofs.deploy(
-      { period, timeout, downtime, zkeyHash: "" },
+      { period, timeout, downtime, zkeyHash: "", downtimeProduct },
       verifier.address
     )
   })

test/examples.js

@@ -14,6 +14,7 @@ const exampleConfiguration = () => ({
     timeout: 5,
     downtime: 64,
     zkeyHash: "",
+    downtimeProduct: 67,
   },
 })