reduce external calls, looks cleaner

contracts/Challenge.sol

@@ -12,6 +12,7 @@ interface IMIPSMemory {
   function ReadMemory(bytes32 stateHash, uint32 addr) external view returns (uint32);
   function ReadBytes32(bytes32 stateHash, uint32 addr) external view returns (bytes32);
   function WriteMemory(bytes32 stateHash, uint32 addr, uint32 val) external pure returns (bytes32);
+  function WriteBytes32(bytes32 stateHash, uint32 addr, bytes32 val) external pure returns (bytes32);
 }
 
 contract Challenge {
@@ -50,14 +51,6 @@ contract Challenge {
 
   // memory helpers
 
-  function writeBytes32(bytes32 stateHash, uint32 addr, bytes32 val) internal view returns (bytes32) {
-    for (uint32 i = 0; i < 32; i += 4) {
-      uint256 tv = uint256(val>>(224-(i*8)));
-
-      stateHash = mem.WriteMemory(stateHash, addr+i, uint32(tv));
-    }
-    return stateHash;
-  }
 
   // create challenge
   uint256 public lastChallengeId = 0;
@@ -100,12 +93,12 @@ contract Challenge {
     // the first instruction executed in MIPS should be an access of startState
     // parentblockhash, txhash, coinbase, unclehash, gaslimit, time
     bytes32 startState = GlobalStartState;
-    startState = writeBytes32(startState, 0x30000000, parentHash);
-    startState = writeBytes32(startState, 0x30000020, Lib_RLPReader.readBytes32(blockNp1[4]));
-    startState = writeBytes32(startState, 0x30000040, bytes32(uint256(Lib_RLPReader.readAddress(blockNp1[2]))));
-    startState = writeBytes32(startState, 0x30000060, Lib_RLPReader.readBytes32(blockNp1[1]));
-    startState = writeBytes32(startState, 0x30000080, bytes32(Lib_RLPReader.readUint256(blockNp1[9])));
-    startState = writeBytes32(startState, 0x300000a0, bytes32(Lib_RLPReader.readUint256(blockNp1[11])));
+    startState = mem.WriteBytes32(startState, 0x30000000, parentHash);
+    startState = mem.WriteBytes32(startState, 0x30000020, Lib_RLPReader.readBytes32(blockNp1[4]));
+    startState = mem.WriteBytes32(startState, 0x30000040, bytes32(uint256(Lib_RLPReader.readAddress(blockNp1[2]))));
+    startState = mem.WriteBytes32(startState, 0x30000060, Lib_RLPReader.readBytes32(blockNp1[1]));
+    startState = mem.WriteBytes32(startState, 0x30000080, bytes32(Lib_RLPReader.readUint256(blockNp1[9])));
+    startState = mem.WriteBytes32(startState, 0x300000a0, bytes32(Lib_RLPReader.readUint256(blockNp1[11])));
 
     // confirm the finalSystemHash asserts the state you claim (in $t0-$t7) and the machine is stopped
     // you must load these proofs into MIPS before calling this

contracts/MIPSMemory.sol

@@ -65,6 +65,14 @@ contract MIPSMemory {
     return newstateHash;
   }
 
+  function WriteBytes32(bytes32 stateHash, uint32 addr, bytes32 val) public pure returns (bytes32) {
+    for (uint32 i = 0; i < 32; i += 4) {
+      uint256 tv = uint256(val>>(224-(i*8)));
+      stateHash = WriteMemory(stateHash, addr+i, uint32(tv));
+    }
+    return stateHash;
+  }
+
   // needed for preimage oracle
   function ReadBytes32(bytes32 stateHash, uint32 addr) public view returns (bytes32) {
     uint256 ret = 0;