| // Copyright (c) 2009 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| // A DifferenceEstimator class provides a means for quickly estimating the |
| // difference between two regions of memory. |
| |
| #ifndef COURGETTE_DIFFERENCE_ESTIMATOR_H_ |
| #define COURGETTE_DIFFERENCE_ESTIMATOR_H_ |
| |
| #include <stddef.h> |
| |
| #include <vector> |
| |
| #include "base/macros.h" |
| #include "courgette/region.h" |
| |
| namespace courgette { |
| |
| // A DifferenceEstimator simplifies the task of determining which 'Subject' byte |
| // strings (stored in regions of memory) are good matches to existing 'Base' |
| // regions. The ultimate measure would be to try full differential compression |
| // and measure the output size, but an estimate that correlates well with the |
| // full compression is more efficient. |
| // |
| // The measure is asymmetric, if the Subject is a small substring of the Base |
| // then it should match very well. |
| // |
| // The comparison is staged: first make Base and Subject objects for the regions |
| // and then call 'Measure' to get the estimate. The staging allows multiple |
| // comparisons to be more efficient by precomputing information used in the |
| // comparison. |
| // |
| class DifferenceEstimator { |
| public: |
| DifferenceEstimator(); |
| ~DifferenceEstimator(); |
| |
| class Base; |
| class Subject; |
| |
| // This DifferenceEstimator owns the objects returned by MakeBase and |
| // MakeSubject. Caller continues to own memory at |region| and must not free |
| // it until ~DifferenceEstimator has been called. |
| Base* MakeBase(const Region& region); |
| Subject* MakeSubject(const Region& region); |
| |
| // Returns a value correlated with the size of the bsdiff or xdelta difference |
| // from |base| to |subject|. Returns zero iff the base and subject regions |
| // are bytewise identical. |
| size_t Measure(Base* base, Subject* subject); |
| |
| private: |
| std::vector<Base*> owned_bases_; |
| std::vector<Subject*> owned_subjects_; |
| DISALLOW_COPY_AND_ASSIGN(DifferenceEstimator); |
| }; |
| |
| } // namespace |
| |
| #endif // COURGETTE_DIFFERENCE_ESTIMATOR_H_ |