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Strings.sol

pragma solidity ^0.4.0;

library Strings {
    function concat(string _base, string _value) internal 
                returns(string) 
    {   
        // By default, the type is storage but the value returned by bytes()
        // is a memory pointer so explicitely mention that
        // In order to modify string, you need to convert it to bytes
        // string stores the UTF-8 format which can have > 1 byte
        // bytes stores the raw byte format, where 2nd byte need not mean
        // the 2nd character and its length need not mean the number of characters
        //
        bytes memory _baseBytes = bytes(_base);
        
        bytes memory _valueBytes = bytes(_value);
        
        string memory _tmpValue = new string(_baseBytes.length + _valueBytes.length);
        bytes memory _newValue = bytes(_tmpValue);
        
        uint i;
        uint j;
        for (i = 0; i < _baseBytes.length; i++) {
            _newValue[j++] = _baseBytes[i];
        }
        
        for (i = 0; i < _valueBytes.length; i++) {
            _newValue[j++] = _valueBytes[i];
        }
        
        return string(_newValue);
    }
    
    function strpos(string _base, string _value) internal
                returns (int)
    {
        bytes memory _baseBytes = bytes(_base);
        bytes memory _valueBytes = bytes(_value);
        
        assert(_valueBytes.length == 1);
        
        for (uint i = 0; i < _baseBytes.length; i++) {
            if (_baseBytes[i] == _valueBytes[0]) {
                return int(i);
            }
        }
        
        return -1;
    }
}

contract TestStrings {
    using Strings for string;
    
    function testConcat(string _base) public returns (string) {
        return _base.concat("_suffix");
    }
    
    function testStrPos(string _base, string _value) public returns (int) {
        return _base.strpos(_value);
    }
}