c++ bsdiff算法

bsdiff算法是一种用于生成两个不同版本文件之间的差异文件的算法。它由Colin Percival创建，并专门用于在软件包管理系统中进行软件更新。

bsdiff算法的核心思想是利用两个不同版本文件之间的相似之处来创建一个小巧的差异文件。首先，它对旧版本文件和新版本文件进行了详细的分析，找出了它们之间的差异。然后，它将这些差异信息用一种高效的方式编码，并生成一个二进制差异文件。

这个差异文件只包含了两个版本文件之间的实际差异，而没有包含完整的新版本文件。因此，它相对于原始文件和新文件的尺寸要小很多。这种压缩的差异文件可以更加高效地传输、存储和处理。

为了将差异文件应用于旧版本文件，需要使用bspatch算法。bspatch算法根据差异文件和旧版本文件，重建出新版本文件。它通过读取差异文件中的指令和数据，并将其应用在旧版本文件上来完成更新的操作。最终，得到的新版本文件与原始的新版本文件完全相同。

总的来说，bsdiff算法在软件更新领域具有重要的应用价值。它能够以较小的开销生成差异文件，从而节省了带宽和存储空间的消耗。同时，它也提供了一种更简单、更高效的方式来升级软件，提升了用户的体验。

相关问题

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：

#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。

C语言实现bsdiff算法

bsdiff算法是一种用于生成增量补丁的算法，它可以快速地生成一个旧版本和新版本之间的差异文件。下面是一个简单的C语言实现示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <bzlib.h>

#define MIN(x, y) ((x) < (y) ? (x) : (y))

// 定义一个结构体，用于保存文件的内容和长度
typedef struct {
    char *data;
    off_t length;
} file_data;

// 读取文件内容到file_data结构体中
file_data read_file(const char *filename) {
    file_data fd = {NULL, 0};
    FILE *fp = fopen(filename, "rb");
    if (fp == NULL) {
        fprintf(stderr, "Unable to open file: %s\n", filename);
        return fd;
    }
    fseek(fp, 0, SEEK_END);
    fd.length = ftell(fp);
    rewind(fp);
    fd.data = (char *)malloc(fd.length);
    if (fd.data == NULL) {
        fclose(fp);
        return fd;
    }
    fread(fd.data, fd.length, 1, fp);
    fclose(fp);
    return fd;
}

// 计算文件的差异
int bsdiff(const char *old_filename, const char *new_filename, const char *patch_filename) {
    file_data old_file = read_file(old_filename);
    if (old_file.data == NULL || old_file.length == 0) {
        fprintf(stderr, "Unable to read old file\n");
        return -1;
    }
    file_data new_file = read_file(new_filename);
    if (new_file.data == NULL || new_file.length == 0) {
        free(old_file.data);
        fprintf(stderr, "Unable to read new file\n");
        return -1;
    }

    FILE *fp = fopen(patch_filename, "wb");
    if (fp == NULL) {
        free(old_file.data);
        free(new_file.data);
        fprintf(stderr, "Unable to create patch file\n");
        return -1;
    }

    // 写入文件头
    fprintf(fp, "BSDIFF40");
    off_t newsize = new_file.length;
    fwrite(&newsize, sizeof(off_t), 1, fp);

    // 分配内存
    char *I = (char *)malloc((old_file.length + 1) * sizeof(char));
    if (I == NULL) {
        fclose(fp);
        free(old_file.data);
        free(new_file.data);
        fprintf(stderr, "Memory allocation error\n");
        return -1;
    }
    char *V = (char *)malloc((old_file.length + 1) * sizeof(char));
    if (V == NULL) {
        fclose(fp);
        free(old_file.data);
        free(new_file.data);
        free(I);
        fprintf(stderr, "Memory allocation error\n");
        return -1;
    }

    // 生成差异
    off_t scan = 0;
    off_t len = 0;
    off_t lastscan = 0;
    off_t lastpos = 0;
    off_t oldsize = old_file.length;
    off_t scsc = 0;
    off_t overlap = 0;
    off_t Sf, lenf, Sb, lenb;
    off_t *pos = (off_t *)malloc((newsize + 1) * sizeof(off_t));
    if (pos == NULL) {
        fclose(fp);
        free(old_file.data);
        free(new_file.data);
        free(I);
        free(V);
        fprintf(stderr, "Memory allocation error\n");
        return -1;
    }
    off_t i;
    for (i = 0; i < newsize; i++) {
        pos[i] = -1;
    }

    // 计算V和I数组
    for (scan = 0; scan < newsize; scan++) {
        char c = new_file.data[scan];
        len = 0;
        for (i = 0; scan + i < newsize; i++) {
            if (new_file.data[scan + i] == c) {
                len++;
            } else {
                break;
            }
        }
        if (len >= 8 && scan + len < newsize) {
            // 计算hash值
            unsigned int h = 0;
            for (i = 0; i < len; i++) {
                h = h * 31 + new_file.data[scan + i];
            }
            // 将hash值添加到pos数组中
            for (i = MIN(oldsize - 1, h % (oldsize - 1));; i--) {
                if (pos[i] == -1) {
                    pos[i] = h % (oldsize - 1);
                    break;
                }
                if (i == 0) {
                    i = oldsize;
                }
            }
        }
    }
    // 计算V和I数组
    i = 0;
    // V[0] = 0;
    for (i = 0; i < oldsize; i++) {
        V[i] = 0;
    }
    for (i = 0; i < newsize; i++) {
        char c = new_file.data[i];
        len = 0;
        for (off_t j = i; j < newsize; j++) {
            if (new_file.data[j] == c) {
                len++;
            } else {
                break;
            }
        }
        if (len >= 8 && i + len < newsize) {
            unsigned int h = 0;
            for (off_t j = 0; j < len; j++) {
                h = h * 31 + new_file.data[i + j];
            }
            off_t posn = pos[h % (oldsize - 1)];
            if (posn != -1) {
                off_t delta = i - posn;
                off_t j = 0;
                while (i + j < newsize && posn + j < oldsize && new_file.data[i + j] == old_file.data[posn + j]) {
                    j++;
                }
                if (j > overlap) {
                    Sf = i;
                    lenf = j - overlap;
                    Sb = posn + j;
                    lenb = j - overlap;
                    overlap = j;
                }
                if (j == overlap && i - posn < delta) {
                    Sf = i;
                    lenf = j - overlap;
                    Sb = posn + j;
                    lenb = delta - overlap;
                    overlap = j;
                }
            }
        }
        V[i] = overlap;
        I[i] = Sf;
    }
    free(pos);

    // 写入差异
    off_t scanpos = 0;
    off_t lenpos = 0;
    fwrite(&lenf, sizeof(off_t), 1, fp);
    fwrite(&lenb, sizeof(off_t), 1, fp);
    fwrite(&Sf, sizeof(off_t), 1, fp);
    fwrite(&Sb, sizeof(off_t), 1, fp);
    fwrite(&new_file.data[0], lenf, 1, fp);
    for (scanpos = lenf, lenpos = lenf; scanpos < newsize;) {
        off_t i = 0, j = 0;
        for (i = 0; scanpos + i < newsize; i++) {
            j = I[scanpos + i] + lenf;
            if (scanpos + i + lenpos < newsize && j + lenpos < oldsize && new_file.data[scanpos + i + lenpos] == old_file.data[j + lenpos]) {
                continue;
            }
            break;
        }
        if (i != 0) {
            fwrite(&i, sizeof(off_t), 1, fp);
        } else {
            j = scanpos + lenpos;
            for (i = lenpos; i < newsize - scanpos; i++) {
                if (V[scanpos + i] >= j - scanpos) {
                    j = i + scanpos;
                }
            }
            i = j - scanpos;
            fwrite(&i, sizeof(off_t), 1, fp);
        }
        fwrite(&new_file.data[scanpos], i, 1, fp);
        for (off_t k = 0; k < i; k++) {
            if (scanpos + k < newsize) {
                V[scanpos + k] = V[scanpos + k] - i;
            }
        }
        scanpos += i;
        lenpos = i;
    }

    // 释放内存
    free(I);
    free(V);
    free(old_file.data);
    free(new_file.data);
    fclose(fp);

    return 0;
}

int main(int argc, char *argv[]) {
    if (argc != 4) {
        fprintf(stderr, "Usage: %s oldfile newfile patchfile\n", argv[0]);
        return -1;
    }
    if (bsdiff(argv[1], argv[2], argv[3]) != 0) {
        return -1;
    }
    return 0;
}

需要注意的是，这个实现只是一个简单的示例，可能不适用于所有情况。在实际应用中，还需要进行更多的测试和优化。