library RLPReader {
  uint8 constant STRING_SHORT_START = 0x80;
  uint8 constant STRING_LONG_START = 0xb8;
  uint8 constant LIST_SHORT_START = 0xc0;
  uint8 constant LIST_LONG_START = 0xf8;
  uint8 constant WORD_SIZE = 32;

  struct RLPItem {
    uint256 len;
    uint256 memPtr;
  }

  struct Iterator {
    RLPItem item; // Item that's being iterated over.
    uint256 nextPtr; // Position of the next item in the list.
  }

  /*
   * @dev Returns the next element in the iteration. Reverts if it has not next element.
   * @param self The iterator.
   * @return The next element in the iteration.
   */
  function next(Iterator memory self) internal pure returns (RLPItem memory) {
    require(hasNext(self));

    uint256 ptr = self.nextPtr;
    uint256 itemLength = _itemLength(ptr);
    self.nextPtr = ptr + itemLength;

    return RLPItem(itemLength, ptr);
  }

  /*
   * @dev Returns true if the iteration has more elements.
   * @param self The iterator.
   * @return true if the iteration has more elements.
   */
  function hasNext(Iterator memory self) internal pure returns (bool) {
    RLPItem memory item = self.item;
    return self.nextPtr < item.memPtr + item.len;
  }

  /*
   * @param item RLP encoded bytes
   */
  function toRlpItem(bytes memory item) internal pure returns (RLPItem memory) {
    uint256 memPtr;
    assembly {
      memPtr := add(item, 0x20)
    }

    return RLPItem(item.length, memPtr);
  }

  /*
   * @dev Create an iterator. Reverts if item is not a list.
   * @param self The RLP item.
   * @return An 'Iterator' over the item.
   */
  function iterator(RLPItem memory self) internal pure returns (Iterator memory) {
    require(isList(self));

    uint256 ptr = self.memPtr + _payloadOffset(self.memPtr);
    return Iterator(self, ptr);
  }

  /*
   * @param item RLP encoded bytes
   */
  function rlpLen(RLPItem memory item) internal pure returns (uint256) {
    return item.len;
  }

  /*
   * @param item RLP encoded bytes
   */
  function payloadLen(RLPItem memory item) internal pure returns (uint256) {
    return item.len - _payloadOffset(item.memPtr);
  }

  /*
   * @param item RLP encoded list in bytes
   */
  function toList(RLPItem memory item) internal pure returns (RLPItem[] memory) {
    require(isList(item));

    uint256 items = numItems(item);
    RLPItem[] memory result = new RLPItem[](items);

    uint256 memPtr = item.memPtr + _payloadOffset(item.memPtr);
    uint256 dataLen;
    for (uint256 i = 0; i < items; i++) {
      dataLen = _itemLength(memPtr);
      result[i] = RLPItem(dataLen, memPtr);
      memPtr = memPtr + dataLen;
    }

    return result;
  }

  // @return indicator whether encoded payload is a list. negate this function call for isData.
  function isList(RLPItem memory item) internal pure returns (bool) {
    if (item.len == 0) return false;

    uint8 byte0;
    uint256 memPtr = item.memPtr;
    assembly {
      byte0 := byte(0, mload(memPtr))
    }

    if (byte0 < LIST_SHORT_START) return false;
    return true;
  }

  /*
   * @dev A cheaper version of keccak256(toRlpBytes(item)) that avoids copying memory.
   * @return keccak256 hash of RLP encoded bytes.
   */
  function rlpBytesKeccak256(RLPItem memory item) internal pure returns (bytes32) {
    uint256 ptr = item.memPtr;
    uint256 len = item.len;
    bytes32 result;
    assembly {
      result := keccak256(ptr, len)
    }
    return result;
  }

  function payloadLocation(RLPItem memory item) internal pure returns (uint256, uint256) {
    uint256 offset = _payloadOffset(item.memPtr);
    uint256 memPtr = item.memPtr + offset;
    uint256 len = item.len - offset; // data length
    return (memPtr, len);
  }

  /*
   * @dev A cheaper version of keccak256(toBytes(item)) that avoids copying memory.
   * @return keccak256 hash of the item payload.
   */
  function payloadKeccak256(RLPItem memory item) internal pure returns (bytes32) {
    (uint256 memPtr, uint256 len) = payloadLocation(item);
    bytes32 result;
    assembly {
      result := keccak256(memPtr, len)
    }
    return result;
  }

  /** RLPItem conversions into data types **/

  // @returns raw rlp encoding in bytes
  function toRlpBytes(RLPItem memory item) internal pure returns (bytes memory) {
    bytes memory result = new bytes(item.len);
    if (result.length == 0) return result;

    uint256 ptr;
    assembly {
      ptr := add(0x20, result)
    }

    copy(item.memPtr, ptr, item.len);
    return result;
  }

  // any non-zero byte is considered true
  function toBoolean(RLPItem memory item) internal pure returns (bool) {
    require(item.len == 1);
    uint256 result;
    uint256 memPtr = item.memPtr;
    assembly {
      result := byte(0, mload(memPtr))
    }

    return result == 0 ? false : true;
  }

  function toAddress(RLPItem memory item) internal pure returns (address) {
    // 1 byte for the length prefix
    require(item.len == 21);

    return address(uint160(toUint(item)));
  }

  function toUint(RLPItem memory item) internal pure returns (uint256) {
    require(item.len > 0 && item.len <= 33);

    uint256 offset = _payloadOffset(item.memPtr);
    uint256 len = item.len - offset;

    uint256 result;
    uint256 memPtr = item.memPtr + offset;
    assembly {
      result := mload(memPtr)

      // shfit to the correct location if neccesary
      if lt(len, 32) {
        result := div(result, exp(256, sub(32, len)))
      }
    }

    return result;
  }

  // enforces 32 byte length
  function toUintStrict(RLPItem memory item) internal pure returns (uint256) {
    // one byte prefix
    require(item.len == 33);

    uint256 result;
    uint256 memPtr = item.memPtr + 1;
    assembly {
      result := mload(memPtr)
    }

    return result;
  }

  function toBytes(RLPItem memory item) internal pure returns (bytes memory) {
    require(item.len > 0);

    uint256 offset = _payloadOffset(item.memPtr);
    uint256 len = item.len - offset; // data length
    bytes memory result = new bytes(len);

    uint256 destPtr;
    assembly {
      destPtr := add(0x20, result)
    }

    copy(item.memPtr + offset, destPtr, len);
    return result;
  }

  /*
   * Private Helpers
   */

  // @return number of payload items inside an encoded list.
  function numItems(RLPItem memory item) private pure returns (uint256) {
    if (item.len == 0) return 0;

    uint256 count = 0;
    uint256 currPtr = item.memPtr + _payloadOffset(item.memPtr);
    uint256 endPtr = item.memPtr + item.len;
    while (currPtr < endPtr) {
      currPtr = currPtr + _itemLength(currPtr); // skip over an item
      count++;
    }

    return count;
  }

  // @return entire rlp item byte length
  function _itemLength(uint256 memPtr) private pure returns (uint256) {
    uint256 itemLen;
    uint256 byte0;
    assembly {
      byte0 := byte(0, mload(memPtr))
    }

    if (byte0 < STRING_SHORT_START) itemLen = 1;
    else if (byte0 < STRING_LONG_START) itemLen = byte0 - STRING_SHORT_START + 1;
    else if (byte0 < LIST_SHORT_START) {
      assembly {
        let byteLen := sub(byte0, 0xb7) // # of bytes the actual length is
        memPtr := add(memPtr, 1) // skip over the first byte
        /* 32 byte word size */
        let dataLen := div(mload(memPtr), exp(256, sub(32, byteLen))) // right shifting to get the len
        itemLen := add(dataLen, add(byteLen, 1))
      }
    } else if (byte0 < LIST_LONG_START) {
      itemLen = byte0 - LIST_SHORT_START + 1;
    } else {
      assembly {
        let byteLen := sub(byte0, 0xf7)
        memPtr := add(memPtr, 1)

        let dataLen := div(mload(memPtr), exp(256, sub(32, byteLen))) // right shifting to the correct length
        itemLen := add(dataLen, add(byteLen, 1))
      }
    }

    return itemLen;
  }

  // @return number of bytes until the data
  function _payloadOffset(uint256 memPtr) private pure returns (uint256) {
    uint256 byte0;
    assembly {
      byte0 := byte(0, mload(memPtr))
    }

    if (byte0 < STRING_SHORT_START) return 0;
    else if (byte0 < STRING_LONG_START || (byte0 >= LIST_SHORT_START && byte0 < LIST_LONG_START)) return 1;
    else if (byte0 < LIST_SHORT_START)
      // being explicit
      return byte0 - (STRING_LONG_START - 1) + 1;
    else return byte0 - (LIST_LONG_START - 1) + 1;
  }

  /*
   * @param src Pointer to source
   * @param dest Pointer to destination
   * @param len Amount of memory to copy from the source
   */
  function copy(
    uint256 src,
    uint256 dest,
    uint256 len
  ) private pure {
    if (len == 0) return;

    // copy as many word sizes as possible
    for (; len >= WORD_SIZE; len -= WORD_SIZE) {
      assembly {
        mstore(dest, mload(src))
      }

      src += WORD_SIZE;
      dest += WORD_SIZE;
    }

    if (len == 0) return;

    // left over bytes. Mask is used to remove unwanted bytes from the word
    uint256 mask = 256**(WORD_SIZE - len) - 1;

    assembly {
      let srcpart := and(mload(src), not(mask)) // zero out src
      let destpart := and(mload(dest), mask) // retrieve the bytes
      mstore(dest, or(destpart, srcpart))
    }
  }
}
function _itemLength(uint256 memPtr) private pure returns (uint256) {
  uint256 itemLen;
  uint256 byte0;
  assembly {
    byte0 := byte(0, mload(memPtr))
  }

  if (byte0 < STRING_SHORT_START) itemLen = 1;
  else if (byte0 < STRING_LONG_START) itemLen = byte0 - STRING_SHORT_START + 1;
  else if (byte0 < LIST_SHORT_START) {
    assembly {
      let byteLen := sub(byte0, 0xb7) // # of bytes the actual length is
      memPtr := add(memPtr, 1) // skip over the first byte
      /* 32 byte word size */
      let dataLen := div(mload(memPtr), exp(256, sub(32, byteLen))) // right shifting to get the len
      itemLen := add(dataLen, add(byteLen, 1))
    }
  } else if (byte0 < LIST_LONG_START) {
    itemLen = byte0 - LIST_SHORT_START + 1;
  } else {
    assembly {
      let byteLen := sub(byte0, 0xf7)
      memPtr := add(memPtr, 1)

      let dataLen := div(mload(memPtr), exp(256, sub(32, byteLen))) // right shifting to the correct length
      itemLen := add(dataLen, add(byteLen, 1))
    }
  }

  return itemLen;
}

// @return entire rlp item byte length