在我們嵌入式開(kāi)發(fā)中，通信中有些數(shù)據(jù)量較大的數(shù)據(jù)可以壓縮之后再進(jìn)行傳輸。

壓縮算法有很多，常用的有如下幾種：

• lz4壓縮算法
• zstd壓縮算法
• xz壓縮算法
• gzip壓縮算法

本次來(lái)介紹壓縮界的速度之王——lz4壓縮庫(kù)。一些數(shù)據(jù)如：

lz4源碼下載鏈接：

http://security.ubuntu.com/ubuntu/pool/main/l/lz4/

lz4的使用

首先，從上面的鏈接中下載源碼進(jìn)行編譯：

然后在源碼根目錄創(chuàng)建一個(gè)文件夾lz4_x86_lib：

編譯lz4：

make
make install PREFIX=$(pwd)/lz4_x86_lib

得到：

lz4庫(kù)交叉編譯可參照：https://blog.csdn.net/nh5431313/article/details/106387168

lz4庫(kù)有幾套壓縮、解壓接口，我們使用最簡(jiǎn)單的接口：

int LZ4_compress_default(const char* source, char* dest, int sourceSize, int maxDestSize);
int LZ4_decompress_safe (const char* source, char* dest, int compressedSize, int maxDecompressedSize);

測(cè)試?yán)樱?/span>

把字符串"12345678901234567890123456789012345678901234567890"進(jìn)行l(wèi)z4壓縮，再解壓，再把解壓之后的內(nèi)容打印出來(lái)。

編寫(xiě)測(cè)試代碼：

// 微信公眾號(hào)：嵌入式大雜燴
#include 
#include 
#include 
#include 
#include 
#include "lz4.h"

long long get_sys_time_us(void)
{
    longlong time_us = 0;
    struct timeval sys_current_time;

    gettimeofday(&sys_current_time, NULL);
    time_us = (longlong)sys_current_time.tv_sec*1000000 + sys_current_time.tv_usec;

    return time_us;
}

int main(int arc, char *argv[])
{
    // 壓縮
    char *src0 = "12345678901234567890123456789012345678901234567890";
    char dst0[64] = {0};
int src0_size = strlen(src0) + 1;
    int max_dst0_size = sizeof(dst0);
    int dst0_compress_size = 0;

printf("before compress = %s, bytes = %d\n", src0, src0_size);
    if (src0_size < max_dst0_size)
    {
        longlong compress_start_time = get_sys_time_us();
        dst0_compress_size = LZ4_compress_default(src0, dst0, src0_size, max_dst0_size);
        longlong compress_end_time = get_sys_time_us();
        printf("after compress = %s\n", dst0);
        printf("compress_time = %lld us\n", compress_end_time - compress_start_time);
    }
else
    {
        printf("compress error! src0_size >= max_dst0_size\n");
    }

    // 解壓
    char src1[64] = {0};
    char dst1[64] = {0};
    int compressed_size = dst0_compress_size;
    int max_decompressed_size = sizeof(dst1);
    int dst1_decompress_size = 0;

    if (dst0_compress_size < max_decompressed_size)
    {
        memcpy(src1, dst0, dst0_compress_size);
        printf("before decompress = %s\n", src1);
    }
    else
    {
        printf("dst0_compress_size >= max_decompressed_size\n");
    }

    if (compressed_size < max_decompressed_size)
    {
        longlong decompress_start_time = get_sys_time_us();
        dst1_decompress_size = LZ4_decompress_safe(src1, dst1, compressed_size, max_decompressed_size);
        longlong decompress_end_time = get_sys_time_us();
        printf("after decompress = %s, bytes = %d\n", dst1, dst1_decompress_size);
        printf("decompress_time = %lld us\n", decompress_end_time - decompress_start_time);
    }
else
    {
        printf("decompress error! compressed_size >= max_decompressed_size\n");
    }

return0;
}

編譯運(yùn)行：

gcc -o lz4_test lz4_test.c -Llz4_x86_lib/lib -Ilz4_x86_lib/include -llz4
./lz4_test