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140 lines
4.2 KiB
C++
140 lines
4.2 KiB
C++
//
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// TapeParser.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/09/2016.
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// Copyright © 2016 Thomas Harte. All rights reserved.
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//
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#ifndef TapeParser_hpp
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#define TapeParser_hpp
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#include "../Tape.hpp"
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#include <memory>
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#include <vector>
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#include <assert.h>
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namespace Storage {
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namespace Tape {
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/*!
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A partly-abstract base class to help in the authorship of tape format parsers;
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provides hooks for pulse classification from pulses to waves and for symbol identification from
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waves.
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Very optional, not intended to box in the approaches taken for analysis.
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*/
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template <typename WaveType, typename SymbolType> class Parser {
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public:
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/// Instantiates a new parser with the supplied @c tape.
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Parser() : has_next_symbol_(false), error_flag_(false) {}
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/// Resets the error flag.
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void reset_error_flag() { error_flag_ = false; }
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/// @returns @c true if an error has occurred since the error flag was last reset; @c false otherwise.
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bool get_error_flag() { return error_flag_; }
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/*!
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Asks the parser to continue taking pulses from the tape until either the subclass next declares a symbol
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or the tape runs out, returning the most-recently declared symbol.
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*/
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SymbolType get_next_symbol(const std::shared_ptr<Storage::Tape::Tape> &tape) {
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while(!has_next_symbol_ && !tape->is_at_end()) {
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process_pulse(tape->get_next_pulse());
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}
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if(tape->is_at_end()) mark_end();
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has_next_symbol_ = false;
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return next_symbol_;
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}
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/*!
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This class provides a single token of lookahead; return_symbol allows the single previous
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token supplied by get_next_symbol to be returned, in which case it will be the thing returned
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by the next call to get_next_symbol.
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*/
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void return_symbol(SymbolType symbol) {
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assert(!has_next_symbol_);
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has_next_symbol_ = true;
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next_symbol_ = symbol;
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}
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/*!
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Should be implemented by subclasses. Consumes @c pulse. Is likely either to call @c push_wave
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or to take no action.
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*/
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virtual void process_pulse(Storage::Tape::Tape::Pulse pulse) = 0;
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/*!
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An optional implementation for subclasses; called to announce that the tape has ended: that
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no more process_pulse calls will occur.
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*/
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virtual void mark_end() {}
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protected:
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/*!
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Adds @c wave to the back of the list of recognised waves and calls @c inspect_waves to check for a new symbol.
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Expected to be called by subclasses from @c process_pulse as and when recognised waves arise.
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*/
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void push_wave(WaveType wave) {
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wave_queue_.push_back(wave);
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inspect_waves(wave_queue_);
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}
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/*!
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Removes @c nunber_of_waves waves from the front of the list.
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Expected to be called by subclasses from @c process_pulse if it is recognised that the first set of waves
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do not form a valid symbol.
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*/
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void remove_waves(int number_of_waves) {
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wave_queue_.erase(wave_queue_.begin(), wave_queue_.begin()+number_of_waves);
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}
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/*!
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Sets @c symbol as the newly-recognised symbol and removes @c nunber_of_waves waves from the front of the list.
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Expected to be called by subclasses from @c process_pulse when it recognises that the first @c number_of_waves
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waves together represent @c symbol.
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*/
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void push_symbol(SymbolType symbol, int number_of_waves) {
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has_next_symbol_ = true;
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next_symbol_ = symbol;
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remove_waves(number_of_waves);
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}
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void set_error_flag() {
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error_flag_ = true;
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}
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/*!
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@returns `true` if there is no data left on the tape and the WaveType queue has been exhausted; `false` otherwise.
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*/
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bool is_at_end(const std::shared_ptr<Storage::Tape::Tape> &tape) {
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return tape->is_at_end() && wave_queue_.empty() && !has_next_symbol_;
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}
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private:
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bool error_flag_;
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/*!
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Should be implemented by subclasses. Inspects @c waves for a potential new symbol. If one is
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found should call @c push_symbol. May wish alternatively to call @c remove_waves to have entries
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removed from the start of @c waves that cannot form a valid symbol. Need not do anything while
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the waves at the start of @c waves may end up forming a symbol but the symbol is not yet complete.
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*/
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virtual void inspect_waves(const std::vector<WaveType> &waves) = 0;
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std::vector<WaveType> wave_queue_;
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SymbolType next_symbol_;
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bool has_next_symbol_;
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};
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}
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}
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#endif /* TapeParser_hpp */
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