touch ups

contracts/MIPS.sol

@@ -128,7 +128,9 @@ contract MIPS {
       return stateHash;
     }
     newStateHash = stepPC(stateHash, pc, pc+4);
-    emit Stepped(newStateHash);
+    if (address(m) != address(0)) {
+      emit Stepped(newStateHash);
+    }
   }
 
   // will revert if any required input state is missing
@@ -180,22 +182,6 @@ contract MIPS {
       storeAddr = rtReg;
     }
 
-
-    // memory fetch (all I-type)
-    // we do the load for stores also
-    uint32 mem;
-    if (opcode >= 0x20) {
-      // M[R[rs]+SignExtImm]
-      uint32 SignExtImm = SE(insn&0xFFFF, 16);
-      rs += SignExtImm;
-      uint32 addr = rs & 0xFFFFFFFC;
-      mem = ReadMemory(stateHash, addr);
-      if (opcode >= 0x28 && opcode != 0x30) {
-        // store
-        storeAddr = addr;
-      }
-    }
-
     if ((opcode >= 4 && opcode < 8) || opcode == 1) {
       bool shouldBranch = false;
 
@@ -221,6 +207,21 @@ contract MIPS {
 
     }
 
+    // memory fetch (all I-type)
+    // we do the load for stores also
+    uint32 mem;
+    if (opcode >= 0x20) {
+      // M[R[rs]+SignExtImm]
+      uint32 SignExtImm = SE(insn&0xFFFF, 16);
+      rs += SignExtImm;
+      uint32 addr = rs & 0xFFFFFFFC;
+      mem = ReadMemory(stateHash, addr);
+      if (opcode >= 0x28 && opcode != 0x30) {
+        // store
+        storeAddr = addr;
+      }
+    }
+
     // ALU
     uint32 val = execute(insn, rs, rt, mem);
 

contracts/MIPSMemory.sol

@@ -61,7 +61,7 @@ contract MIPSMemory {
     return ret;
   }
 
-  function fb(bytes memory dat) internal view returns (uint32) {
+  function fb(bytes memory dat) internal pure returns (uint32) {
     require(dat.length == 4, "wrong length value");
     uint32 ret = uint32(uint8(dat[0])) << 24 |
                  uint32(uint8(dat[1])) << 16 |

contracts/lib/Lib_MerkleTrie.sol

@@ -89,7 +89,7 @@ library Lib_MerkleTrie {
         return _getUpdatedTrieRoot(newPath, _key, trie);
     }
 
-    function getRawNode(bytes memory encoded) private view returns (TrieNode memory) {
+    function getRawNode(bytes memory encoded) private pure returns (TrieNode memory) {
         return TrieNode({
             encoded: encoded,
             decoded: Lib_RLPReader.readList(encoded)
@@ -97,7 +97,9 @@ library Lib_MerkleTrie {
     }
 
     function getTrieNode(mapping(bytes32 => bytes) storage trie, bytes32 nodeId) private view returns (TrieNode memory) {
-        return getRawNode(trie[nodeId]);
+        bytes memory encoded = trie[nodeId];
+        require(keccak256(encoded) == nodeId, "bad hash in trie lookup");
+        return getRawNode(encoded);
     }
 
     /**