用C++实现bsdiff算法。

bsdiff算法是一种用于生成两个二进文件之间差异的算法，常用于软件升级和增量更新。下面是一个C++实现的示例代码： ```c++ #include <fstream> #include <vector> typedef unsigned char uint8_t; typedef unsigned int uint32_t; typedef unsigned long long uint64_t; const uint64_t MAX_LEN = 0xFFFFFFFFFFFFFFFF; class bsdiff { public: static bool diff(const char* old_file, const char* new_file, const char* patch_file); static bool patch(const char* old_file, const char* new_file, const char* patch_file); private: static void split(uint64_t* sa, uint8_t* old_data, uint64_t old_size); static uint64_t search(uint8_t* new_data, uint64_t new_size, uint8_t* old_data, uint64_t old_size, uint64_t pos, uint64_t len, uint64_t* offset); static void encode(std::ofstream& fout, uint64_t x); static void copy(std::ofstream& fout, uint8_t* data, uint64_t size); }; bool bsdiff::diff(const char* old_file, const char* new_file, const char* patch_file) { std::ifstream old_f(old_file, std::ios::binary); if (!old_f) return false; old_f.seekg(0, std::ios::end); uint64_t old_size = old_f.tellg(); old_f.seekg(0, std::ios::beg); std::vector<uint8_t> old_data(old_size); old_f.read(reinterpret_cast<char*>(&old_data[0]), old_size); old_f.close(); std::ifstream new_f(new_file, std::ios::binary); if (!new_f) return false; new_f.seekg(0, std::ios::end); uint64_t new_size = new_f.tellg(); new_f.seekg(0, std::ios::beg); std::vector<uint8_t> new_data(new_size); new_f.read(reinterpret_cast<char*>(&new_data[0]), new_size); new_f.close(); std::ofstream patch_f(patch_file, std::ios::binary); if (!patch_f) return false; uint64_t* sa = new uint64_t[(old_size + 1) / 2]; split(sa, &old_data[0], old_size); uint64_t i = 0; uint64_t len = 0; uint64_t pos = 0; uint64_t last_offset = 0; while (i < new_size) { uint64_t offset = 0; pos = search(&new_data[0], new_size, &old_data[0], old_size, sa[i], old_size - sa[i], &offset); if (i + pos - last_offset >= MAX_LEN || pos == old_size) { encode(patch_f, i - last_offset); encode(patch_f, pos - last_offset); copy(patch_f, &new_data[i], pos - last_offset); last_offset = pos; } i += pos - sa[i]; } encode(patch_f, i - last_offset); encode(patch_f, new_size - last_offset); copy(patch_f, &new_data[i], new_size - last_offset); delete[] sa; patch_f.close(); return true; } bool bsdiff::patch(const char* old_file, const char* new_file, const char* patch_file) { std::ifstream old_f(old_file, std::ios::binary); if (!old_f) return false; old_f.seekg(0, std::ios::end); uint64_t old_size = old_f.tellg(); old_f.seekg(0, std::ios::beg); std::vector<uint8_t> old_data(old_size); old_f.read(reinterpret_cast<char*>(&old_data[0]), old_size); old_f.close(); std::ifstream patch_f(patch_file, std::ios::binary); if (!patch_f) return false; std::ofstream new_f(new_file, std::ios::binary); if (!new_f) return false; uint64_t old_pos = 0; uint64_t new_pos = 0; uint64_t cmd = 0; uint64_t len = 0; while (patch_f) { cmd = 0; len = 0; patch_f.read(reinterpret_cast<char*>(&cmd), sizeof(uint64_t)); patch_f.read(reinterpret_cast<char*>(&len), sizeof(uint64_t)); if (patch_f.eof()) break; if (cmd > 0) { std::vector<uint8_t> diff_data(len); patch_f.read(reinterpret_cast<char*>(&diff_data[0]), len); for (uint64_t i = 0; i < len; i++) { new_f.put(old_data[old_pos + i] + diff_data[i]); } old_pos += len; new_pos += len; } else { new_pos += len; } } patch_f.close(); new_f.close(); return true; } void bsdiff::split(uint64_t* sa, uint8_t* old_data, uint64_t old_size) { uint64_t i = 0; uint64_t j = 0; uint64_t k = 0; uint64_t x = 0; uint64_t y = 0; uint64_t tmp = 0; uint64_t* v = new uint64_t[old_size]; for (i = 0; i < old_size; i++) { v[i] = i; } for (i = 0; i < old_size; i++) { sa[i] = v[0]; v[0] = v[1]; x = v[1]; for (j = 1; j < old_size - i - 1; j++) { y = v[j + 1]; if (old_data[sa[i] + j] > old_data[x + j]) { v[j] = x; x = y; } else if (old_data[sa[i] + j] > old_data[y + j]) { v[j] = sa[i] + j; x = y; } else { v[j] = y; } } v[old_size - i - 2] = x; } for (i = 0; i < old_size; i++) { sa[v[i]] = i; } delete[] v; } uint64_t bsdiff::search(uint8_t* new_data, uint64_t new_size, uint8_t* old_data, uint64_t old_size, uint64_t pos, uint64_t len, uint64_t* offset) { uint64_t start = 0; uint64_t end = old_size; uint64_t x = 0; uint64_t y = 0; uint64_t last = 0; while (start < end) { x = start + (end - start) / 2; last = (x > *offset) ? x - *offset : *offset - x; y = 0; while (y < len && x + y < old_size && new_data[pos + y] == old_data[x + y]) { y++; } if (y == len) { *offset = x; return x - *offset + len; } if (y > last) { end = x; } else { start = x + 1; } } return 0; } void bsdiff::encode(std::ofstream& fout, uint64_t x) { uint8_t buf[10]; uint32_t i = 0; while (x >= 0x80) { buf[i++] = (x & 0x7F) | 0x80; x >>= 7; } buf[i++] = x & 0x7F; for (uint32_t j = 0; j < i; j++) { fout.put(buf[j]); } } void bsdiff::copy(std::ofstream& fout, uint8_t* data, uint64_t size) { for (uint64_t i = 0; i < size; i++) { fout.put(data[i]); } } ``` 该实现使用了STL中的vector和fstream库，代码较为简洁易读。其中，split函数用于计算old_data数组的后缀数组，search函数用于在old_data数组中查找与new_data数组匹配的最长子串。encode和copy函数用于将数据写入输出流中。diff函数用于生成差异文件，patch函数用于根据差异文件生成新文件。