contract c {
    uint a;
    function charAt(bytes32 b, uint char) returns (bytes1) {
        return bytes1(uint8(uint(b) / (2**((31 - char) * 8))));
    }
    function parseDecimal(bytes32 byteString) returns (uint r) {
        uint n = uint(byteString);
        for (uint b = 0; b < 32; b ++)
        {
            var c = uint8(charAt(byteString, b));
            if (c < uint8('0') || c > uint8('9'))
                return;
            r = r * 10 + c - uint8('0');
        }
    }
}