GetDrandByEpoch

Author: wjmelements

README.md

@@ -71,7 +71,7 @@ Additional FVM support can be found in the [filecoin-solidity library](https://g
 | ✅ | CallActorByAddress | `0xfe00000000000000000000000000000000000003` |
 | ❌ | GetActorType | `0xfe00000000000000000000000000000000000004` |
 | ✅ | CallActorById | `0xfe00000000000000000000000000000000000005` |
-| ❌ | GetDrandByEpoch | `0xfe00000000000000000000000000000000000006` |
+| ✅ | GetDrandByEpoch | `0xfe00000000000000000000000000000000000006` |
 
 ### Methods
 

src/Demo.sol

@@ -2,6 +2,7 @@
 pragma solidity ^0.8.30;
 
 import {FVMPay} from "./FVMPay.sol";
+import {FVMRandom} from "./FVMRandom.sol";
 
 contract Demo {
     // baseline solidity methods using CALL opcode
@@ -34,4 +35,19 @@ contract Demo {
     function burn() external payable {
         require(msg.value.burn());
     }
+
+    // randomness
+    using FVMRandom for uint256;
+
+    function prev() external view returns (uint256 randomness) {
+        randomness = (block.number - 1).drand();
+    }
+
+    function curr() external view returns (uint256 randomness) {
+        randomness = block.number.drand();
+    }
+
+    function next() external view returns (uint256 randomness) {
+        randomness = (block.number + 1).drand();
+    }
 }

src/FVMRandom.sol

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+pragma solidity ^0.8.30;
+
+import {GET_DRAND_BY_EPOCH} from "./FVMPrecompiles.sol";
+
+library FVMRandom {
+    // the precompile will assert and consume all gas if epoch > block.number
+    function drand(uint256 epoch) internal view returns (uint256 randomness) {
+        assembly ("memory-safe") {
+            let fmp := mload(0x40)
+            mstore(fmp, epoch)
+            pop(staticcall(gas(), GET_DRAND_BY_EPOCH, fmp, 32, fmp, 32))
+            randomness := mload(fmp)
+        }
+    }
+}

tools/gas-profile.sh

@@ -3,23 +3,36 @@
 RPC_URL=https://api.calibration.node.glif.io/rpc/v1
 
 # Demo.sol
-ADDRESS=0x91A9f1b2Aa333936A15B1F9D399C3c3b8647De6e
+ADDRESS=0x1Ff1ceFcf1739d1b6aD4B2Cd27FB970A3214d174
 
 estimateGas() {
-    curl -H "Content-Type: application/json" -X POST --data "{\"id\": 1, \"method\": \"eth_estimateGas\", \"params\": [{\"to\": \"$ADDRESS\", \"data\": \"$1\", \"value\": \"0x1\"}, \"latest\"]}" $RPC_URL
+    curl -H "Content-Type: application/json" -X POST --data "{\"id\": 1, \"method\": \"eth_estimateGas\", \"params\": [{\"to\": \"$ADDRESS\", \"data\": \"$1\", \"value\": \"$2\"}, \"latest\"]}" $RPC_URL
+}
+
+call() {
+    curl -H "Content-Type: application/json" -X POST --data "{\"id\": 1, \"method\": \"eth_call\", \"params\": [{\"to\": \"$ADDRESS\", \"data\": \"$1\", \"value\": \"$2\"}, \"latest\"]}" $RPC_URL
 }
 
 echo "send(address)"
-estimateGas 0x3e58c58c0000000000000000000000004a6f6b9ff1fc974096f9063a45fd12bd5b928ad1
+estimateGas 0x3e58c58c0000000000000000000000004a6f6b9ff1fc974096f9063a45fd12bd5b928ad1 0x1
 
 echo "transfer(address)"
-estimateGas 0x1a6952300000000000000000000000004a6f6b9ff1fc974096f9063a45fd12bd5b928ad1
+estimateGas 0x1a6952300000000000000000000000004a6f6b9ff1fc974096f9063a45fd12bd5b928ad1 0x1
 
 echo "pay(address)"
-estimateGas 0x0c11dedd0000000000000000000000004a6f6b9ff1fc974096f9063a45fd12bd5b928ad1
+estimateGas 0x0c11dedd0000000000000000000000004a6f6b9ff1fc974096f9063a45fd12bd5b928ad1 0x1
 
 echo "pay(uint64)"
-estimateGas 0x68f165f0000000000000000000000000000000000000000000000000000000000002a9a2
+estimateGas 0x68f165f0000000000000000000000000000000000000000000000000000000000002a9a2 0x1
 
 echo "burn()"
-estimateGas 0x44df8e70
+estimateGas 0x44df8e70 0x1
+
+echo "prev()"
+estimateGas 0x479c9254 0x0
+
+echo "curr()"
+estimateGas 0x8103aa45 0x0
+
+echo "next() (reverts)"
+estimateGas 0x4c8fe526 0x0