用c语言实现lz77压缩算法

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LZ77压缩算法是一种无损压缩算法，它通过寻找重复的字符序列来实现数据压缩。下面是一个简单的C语言实现示例：

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

#define WINDOW_SIZE 15
#define LOOKAHEAD_SIZE 4

typedef struct {
    int offset;
    int length;
    char next;
} LZ77_Triple;

int findMatch(char *window, char *lookahead, int windowPos, int *matchLength) {
    int maxLength = 0;
    int maxOffset = 0;
    int i, j;
    for (i = 0; i < WINDOW_SIZE; i++) {
        int length = 0;
        for (j = 0; j < LOOKAHEAD_SIZE; j++) {
            if (window[(i + j) % WINDOW_SIZE] == lookahead[j]) {
                length++;
            } else {
                break;
            }
        }
        if (length > maxLength) {
            maxLength = length;
            maxOffset = i;
        }
    }
    *matchLength = maxLength;
    return maxOffset;
}

int encode(char *input, int inputLength, char *output) {
    int outputLength = 0;
    int inputPos = 0;
    char window[WINDOW_SIZE] = {0};
    char lookahead[LOOKAHEAD_SIZE] = {0};
    while (inputPos < inputLength) {
        int matchLength = 0;
        int offset = findMatch(window, lookahead, inputPos % WINDOW_SIZE, &matchLength);
        if (matchLength > 0) {
            LZ77_Triple triple = {offset, matchLength, lookahead[matchLength]};
            memcpy(output + outputLength, &triple, sizeof(LZ77_Triple));
            outputLength += sizeof(LZ77_Triple);
            inputPos += matchLength;
        } else {
            LZ77_Triple triple = {0, 0, input[inputPos]};
            memcpy(output + outputLength, &triple, sizeof(LZ77_Triple));
            outputLength += sizeof(LZ77_Triple);
            window[inputPos % WINDOW_SIZE] = input[inputPos];
            inputPos++;
        }
        memmove(lookahead, input + inputPos, LOOKAHEAD_SIZE);
    }
    return outputLength;
}

int decode(char *input, int inputLength, char *output) {
    int outputLength = 0;
    int inputPos = 0;
    char window[WINDOW_SIZE] = {0};
    while (inputPos < inputLength) {
        LZ77_Triple triple;
        memcpy(&triple, input + inputPos, sizeof(LZ77_Triple));
        inputPos += sizeof(LZ77_Triple);
        if (triple.length > 0) {
            int i;
            for (i = 0; i < triple.length; i++) {
                output[outputLength] = window[(triple.offset + i) % WINDOW_SIZE];
                window[(inputPos + i) % WINDOW_SIZE] = output[outputLength];
                outputLength++;
            }
        }
        output[outputLength] = triple.next;
        window[inputPos % WINDOW_SIZE] = output[outputLength];
        outputLength++;
    }
    return outputLength;
}

int main() {
    char input[] = "hello world hello world";
    int inputLength = sizeof(input) - 1;
    int encodedLength = inputLength * sizeof(LZ77_Triple);
    char *encoded = (char*)malloc(encodedLength);
    encode(input, inputLength, encoded);
    printf("Encoded: ");
    int i;
    for (i = 0; i < encodedLength; i++) {
        printf("%02x ", encoded[i] & 0xff);
    }
    printf("\n");
    int decodedLength = inputLength;
    char *decoded = (char*)malloc(decodedLength);
    decode(encoded, encodedLength, decoded);
    printf("Decoded: %s\n", decoded);
    free(encoded);
    free(decoded);
    return 0;
}

在这个示例中，我们定义了`WINDOW_SIZE`和`LOOKAHEAD_SIZE`分别为15和4，这意味着我们将使用最近的15个字符作为窗口和接下来的4个字符作为后续字符。`findMatch`函数用于查找最长匹配，并返回匹配的偏移量和长度。`encode`函数用于将输入字符串编码为LZ77三元组序列，`decode`函数用于将LZ77三元组序列解码为原始字符串。

希望这个示例能对你有所帮助！