decodecontext.hpp

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#ifndef DECODECONTEXT_HPP_INCLUDED
#define DECODECONTEXT_HPP_INCLUDED

#include "codectypedefs.hpp"

#include <map>
#include <stack>
#include <string>
#include <iosfwd>

class DecodeContext
{
public: // construct
    DecodeContext(file_it data_begin,
                  file_it data_end);

public: // read and advance
    std::string
    readFieldValue(std::string const & field_name,
                   unsigned width_of_field_in_bits);
    

    bool finished() const;
    
public: // conditional and loop support
    
    bool testCondition(std::string const & field,
                       std::string const & op,
                       unsigned long const & value) const;
    
public: // loop support
    void registerCRC();
    
    bool testLoopExit();
    
private: // loop support
    void pushLoopExit(unsigned bytes_to_loop_exit);    
    
private: // save values
    void pushFieldValue(std::string const & field,
                        unsigned long const & value);

private: // read and advance
    void getCurrentByte();
    
private:
    unsigned current_byte_; // The current byte from the input stream
    unsigned bits_left_;    // How much of this byte remains to be read
    
    unsigned depth_;        // How deeply nested into the section

    int offset_for_crc_;    // Offset from the end of the section at 
                            // which the last loop ends. Either 4 or 0,
                            // depending on the section type. 
    
    file_it data_begin_;      
    file_it data_end_;
    
    // Record of field values, used in conditional evaluation.
    typedef std::map<std::string, unsigned long> field_values;
    field_values field_values_;
    
    // Stack of file iterators marking loop exits
    std::stack<file_it> loop_exits_;
};

#endif // defined DECODECONTEXT_HPP_INCLUDED

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