Read more than 32 bytes from memory (Assembly)

Question

Assume I am passing a variable bytes (memory) to a function. This variable corresponds to A concatenated with B where A is of size 32 and B is 96 bytes, how can I return A (bytes32) and B (bytes).

function readData(bytes memory data) public returns (bytes32, bytes memory){
    bytes32 A;
    bytes memory B;
    assembly{
        A:= mload(add(data,0x20))
        calldatacopy(B,0x45,0xA0) // not sure about this
    }
    return (A,B);
}

Edit

knowing the length of B make things easy but the things is that B size can change, therefore hardcoding a sequence of mload (one per word of data) won't do. this could be solved with an assembly loop but I wonder if there is a more efficient way to do it.

Answer 1

function readData (bytes memory data)
public pure returns (bytes32 a, bytes memory b) {
  require (data.length == 0x80);
  assembly {
    a := mload (add (data, 0x20)) // A
    b := mload (0x40) // Free memory pointer
    mstore (0x40, add (b, 0x80)) // Advance free memory pointer
    mstore (b, 0x60) // B length
    mstore (add (b, 0x20), mload (add (data, 0x40))) // First word of B
    mstore (add (b, 0x40), mload (add (data, 0x60))) // Second word of B
    mstore (add (b, 0x60), mload (add (data, 0x80))) // Third word of B
  }
}