bytes32 to uint conversion is incorrect

Question

I instantiate the following contract with _number as 10. When I check the value of number, I get 72370055773322622139731865630429942408293740416025352524660990004945706024960. Is this a problem with my contract, or is this a web3 bug?

contract Thing{
  uint public number;
  function Thing(bytes32 _number){
    number = uint(_number);
  }
}

Answer 1

72370055773322622139731865630429942408293740416025352524660990004945706024960 is 0xa000000000000000000000000000000000000000000000000000000000000000L - or 10 in hex, left shifted. Without seeing your web3 code, it's difficult to say why it was parsed this way, but it seems likely web3 treated your input as a single byte byte string, and left-aligned it into the bytes32 argument.

Answer 2

Summary

There are some oddities when using bytes32 as function parameters.

From Solidity Features - Byte Arrays:

PT Basic support for variable-length byte arrays. This includes

• bytes type for storage variables
• msg.data is of bytes type and contains the calldata
• functions taking arbitrary parameters (call, sha3, ...) can be called with bytes arguments.
• copying between msg.data and bytes storage variables

What is not possible yet:

• function parameters of bytes type
• local variables of bytes type
• index or slice access

---

Details

I use the following source code based on your source code:

contract ByteToInt {
    uint public number;
    bytes32 public thebytes32;

    function ByteToInt(bytes32 _number) {
        thebytes32 = _number;
        number = uint(_number);
    }
}

And flattened it to:

var byteToIntSource='contract ByteToInt { uint public number; bytes32 public thebytes32;  function ByteToInt(bytes32 _number) { thebytes32 = _number; number = uint(_number); }}'

Ran it in geth --dev console:

> var byteToIntSource='contract ByteToInt { uint public number; bytes32 public thebytes32;  function ByteToInt(bytes32 _number) { thebytes32 = _number; number = uint(_number); }}'
undefined

Compiled it:

> var byteToIntCompiled = web3.eth.compile.solidity(byteToIntSource);
undefined

Inserted it into the blockchain:

> var byteToIntContract = web3.eth.contract(byteToIntCompiled.ByteToInt.info.abiDefinition);
var byteToInt = byteToIntContract.new(10, {from:web3.eth.accounts[0], data: byteToIntCompiled.ByteToInt.code, gas: 1000000}, 
  function(e, contract) {
    if (!e) {
      if (!contract.address) {
        console.log("Contract transaction send: TransactionHash: " + 
          contract.transactionHash + " waiting to be mined...");
      } else {
        console.log("Contract mined! Address: " + contract.address);
        console.log(contract);
      }
    }
  }
)
...
Contract mined! Address: 0x49617e1728c53a3e31ccf21faf6ba344af90f04c

And checked the values:

> byteToInt.thebytes32()
"0xa000000000000000000000000000000000000000000000000000000000000000"

> byteToInt.number()
7.237005577332262213973186563042994240829374041602535252466099000494570602496e+76

I executed the following statements in Java:

BigInteger num = new BigInteger("a000000000000000000000000000000000000000000000000000000000000000", 16);
System.out.println(num.toString(10));

And the results are:

72370055773322622139731865630429942408293740416025352524660990004945706024960

So 10 is being encoded as the first byte in your bytes32 variable, and the uint(...) cast is converting the whole bytes32 data into a uint.

Checking how web3 converts the decimal values into the parameters, I tried sending in 0xabc into the constructor by using the decimal equivalent of 2748:

var byteToInt = byteToIntContract.new(2748, {from:web3.eth.accounts[0], data: byteToIntCompiled.ByteToInt.code, gas: 1000000}, 
  function(e, contract) {
    if (!e) {
      if (!contract.address) {
        console.log("Contract transaction send: TransactionHash: " + 
          contract.transactionHash + " waiting to be mined...");
      } else {
        console.log("Contract mined! Address: " + contract.address);
        console.log(contract);
      }
    }
  }
)
...
Contract mined! Address: 0xb086848ed791c87a6659ed17fb6fd85e37aae97b
...
> byteToInt.thebytes32()
"0xabc0000000000000000000000000000000000000000000000000000000000000"
> byteToInt.number()
7.7684731744176002203118424512664641303902811977827214350690781458433906311168e+76

Try out the following:

var byteToInt = byteToIntContract.new(0x0000000000000000000000000000000000000000000000000000000000000abc, {from:web3.eth.accounts[0], data: byteToIntCompiled.ByteToInt.code, gas: 1000000}, 
  function(e, contract) {
    if (!e) {
      if (!contract.address) {
        console.log("Contract transaction send: TransactionHash: " + 
          contract.transactionHash + " waiting to be mined...");
      } else {
        console.log("Contract mined! Address: " + contract.address);
        console.log(contract);
      }
    }
  }
)
...
> byteToInt.thebytes32()
"0xabc0000000000000000000000000000000000000000000000000000000000000"