Parse arbitrary bytes input

Question

A function recives bytes as input:

function foo (bytes data)

How do I parse that into individual byte32 chunks?

function foo (bytes data) returns (bytes32[])

My goal is to understand how to handle the Token function:

receiveApproval(address from, uint256 tokens, address token, bytes data)

Answer 1

You can loop over the bytes with an increment of 32:

function foo(bytes memory data) internal pure returns (bytes32[] memory output) {
    require(data.length % 32 == 0);
    output = new bytes32[](data.length / 32);
    for (uint256 i = 32; i <= output.length * 32; i += 32) {
        assembly {mstore(add(output, i), mload(add(data, i)))}
    }
}