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。