C語言實現短字串壓縮的三種方法詳解

2022-08-10 22:00:49

前言

上一篇探索了LZ4的壓縮和解壓效能，以及對LZ4和ZSTD的壓縮、解壓效能進行了橫向對比。文末的最後也給了一個彩蛋：任意長度的字串都可以被ZSTD、LZ4之類的壓縮算壓縮得很好嗎？

本篇我們就來一探究竟。

一、通用演演算法的短字元壓縮

開門見山，我們使用一段比較短的文字：Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.

使用ZSTD與LZ4分別壓縮一下上面這段短文字。下面分別是它們的壓縮結果。

ZSTD：

LZ4：

對短文字的壓縮，zstd的壓縮率很低，lz4壓縮後的文字長度盡然超過了原有字串的長度。這是為什麼？說實話在這之前我也沒想到。

參照兩位大佬的名言：

Are you ok?

What's your problem?

二、短字串壓縮

從上面的結果可以得知，任何壓縮演演算法都有它的使用場景，並不是所有長度的字串都適合被某種演演算法壓縮。一般原因是通用壓縮演演算法維護了被壓縮字串的，用於字串還原的相關資料結構，而這些資料結構的長度超過了被壓縮短字串的自身長度。

那麼問題來了，“我真的有壓縮短字串的需求，我想體驗壓縮的極致感，怎麼辦？”。

短字元壓縮演演算法它來了。這裡挑選了3種比較優異的短字元壓縮演演算法，分別是smaz，shoco，以及壓軸的unisox2。跟前兩章一樣，還是從壓縮率，壓縮和解壓縮效能的角度，一起看看他們在短字元壓縮場景的各自表現吧。

（1）Smaz

1、Smaz的壓縮和解壓縮

#include <stdio.h>
#include <string.h>
#include <iostream>
#include "smaz.h"

using namespace std;

int main()
{
    int buf_len;
    int com_size;
    int decom_size;

    char com_buf[4096] = {0};
    char decom_buf[4096] = {0};

    char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";

    buf_len = strlen(str_buf);
    com_size = smaz_compress(str_buf, buf_len, com_buf, 4096);

    cout << "text size:" << buf_len << endl;
    cout << "compress text size:" << com_size << endl;
    cout << "compress ratio:" << (float)buf_len / (float)com_size << endl << endl;

    decom_size = smaz_decompress(com_buf, com_size, decom_buf, 4096);
    cout << "decompress text size:" << decom_size << endl;

    if(strncmp(str_buf, decom_buf, buf_len)) {
        cout << "decompress text is not equal to source text" << endl;
    }

    return 0;
}

執行結果如下：

通過smaz壓縮後的短字串長度為77，和源字串相比，減少了30Byte。

2、Smaz的壓縮和解壓縮效能

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <sys/time.h>
#include "smaz.h"

using namespace std;

int main()
{
    int cnt = 0;
    int buf_len;
    int com_size;
    int decom_size;

    timeval st, et;

    char *com_ptr = NULL;
    char* decom_ptr = NULL;

    char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";

    buf_len = strlen(str_buf);
    gettimeofday(&st, NULL);
    while(1) {

        com_ptr = (char *)malloc(buf_len);
        com_size = smaz_compress(str_buf, buf_len, com_ptr, buf_len);

        free(com_ptr);
        cnt++;

        gettimeofday(&et, NULL);
        if(et.tv_sec - st.tv_sec >= 10) {
            break;
        }
    }

    cout << endl <<"compress per second:" << cnt/10 << " times" << endl;

    cnt = 0;
    com_ptr = (char *)malloc(buf_len);
    com_size = smaz_compress(str_buf, buf_len, com_ptr, buf_len);

    gettimeofday(&st, NULL);
    while(1) {

        // decompress length not more than origin buf length
        decom_ptr = (char *)malloc(buf_len + 1);
        decom_size = smaz_decompress(com_ptr, com_size, decom_ptr, buf_len + 1);

        // check decompress length
        if(buf_len != decom_size) {
            cout << "decom error" << endl;
        }

        free(decom_ptr);
        cnt++;

        gettimeofday(&et, NULL);
        if(et.tv_sec - st.tv_sec >= 10) {
            break;
        }
    }

    cout << "decompress per second:" << cnt/10 << " times" << endl << endl;

    free(com_ptr);
    return 0;
}

結果如何？

壓縮效能在40w條/S，解壓在百萬級，好像還不錯哈！

（2）Shoco

1、Shoco的壓縮和解壓縮

#include <stdio.h>
#include <string.h>
#include <iostream>
#include "shoco.h"

using namespace std;

int main()
{
    int buf_len;
    int com_size;
    int decom_size;

    char com_buf[4096] = {0};
    char decom_buf[4096] = {0};

    char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";

    buf_len = strlen(str_buf);
    com_size = shoco_compress(str_buf, buf_len, com_buf, 4096);

    cout << "text size:" << buf_len << endl;
    cout << "compress text size:" << com_size << endl;
    cout << "compress ratio:" << (float)buf_len / (float)com_size << endl << endl;

    decom_size = shoco_decompress(com_buf, com_size, decom_buf, 4096);
    cout << "decompress text size:" << decom_size << endl;

    if(strncmp(str_buf, decom_buf, buf_len)) {
        cout << "decompress text is not equal to source text" << endl;
    }

    return 0;
}

執行結果如下：

通過shoco壓縮後的短字串長度為86，和源字串相比，減少了21Byte。壓縮率比smaz要低。

2、Shoco的壓縮和解壓縮效能

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <sys/time.h>
#include "shoco.h"

using namespace std;

int main()
{
    int cnt = 0;
    int buf_len;
    int com_size;
    int decom_size;

    timeval st, et;

    char *com_ptr = NULL;
    char* decom_ptr = NULL;

    char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";

    buf_len = strlen(str_buf);
    gettimeofday(&st, NULL);
    while(1) {

        com_ptr = (char *)malloc(buf_len);
        com_size = shoco_compress(str_buf, buf_len, com_ptr, buf_len);

        free(com_ptr);
        cnt++;

        gettimeofday(&et, NULL);
        if(et.tv_sec - st.tv_sec >= 10) {
            break;
        }
    }

    cout << endl <<"compress per second:" << cnt/10 << " times" << endl;

    cnt = 0;
    com_ptr = (char *)malloc(buf_len);
    com_size = shoco_compress(str_buf, buf_len, com_ptr, buf_len);

    gettimeofday(&st, NULL);
    while(1) {

        // decompress length not more than origin buf length
        decom_ptr = (char *)malloc(buf_len + 1);
        decom_size = shoco_decompress(com_ptr, com_size, decom_ptr, buf_len + 1);

        // check decompress length
        if(buf_len != decom_size) {
            cout << "decom error" << endl;
        }

        free(decom_ptr);
        cnt++;

        gettimeofday(&et, NULL);
        if(et.tv_sec - st.tv_sec >= 10) {
            break;
        }
    }

    cout << "decompress per second:" << cnt/10 << " times" << endl << endl;

    free(com_ptr);
    return 0;
}

執行結果如何呢？

holy shit！壓縮和解壓縮居然都達到了驚人的百萬級。就像演演算法作者們自己說的一樣：“在長字串壓縮領域，shoco不想與通用壓縮演演算法競爭，我們的優勢是短字元的快速壓縮，雖然壓縮率很爛！”。這樣說，好像也沒毛病。

（3）Unisox2

我們再來看看unisox2呢。

1、Unisox2的壓縮和解壓縮

#include <stdio.h>
#include <string.h>
#include "unishox2.h"

int main()
{
    int buf_len;
    int com_size;
    int decom_size;

    char com_buf[4096] = {0};
    char decom_buf[4096] = {0};

    char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";

    buf_len = strlen(str_buf);
    com_size = unishox2_compress_simple(str_buf, buf_len, com_buf);

    printf("text size:%dn", buf_len);
    printf("compress text size:%dn", com_size);
    printf("compress ratio:%fnn", (float)buf_len / (float)com_size);

    decom_size = unishox2_decompress_simple(com_buf, com_size, decom_buf);

    printf("decompress text size:%dn", decom_size);

    if(strncmp(str_buf, decom_buf, buf_len)) {
        printf("decompress text is not equal to source textn");
    }

    return 0;
}

結果如下：

通過Unisox2壓縮後的短字串長度為67，和源字串相比，減少了40Byte，相當於是打了6折啊！不錯不錯。

2、Unisox2的壓縮和解壓縮效能

Unisox2的壓縮能力目前來看是三者中最好的，如果他的壓縮和解壓效能也不錯的話，那就真的就比較完美了。再一起看看Unisox2的壓縮和解壓效能吧！

#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <sys/time.h>
#include "unishox2.h"

int main()
{
    int cnt = 0;
    int buf_len;
    int com_size;
    int decom_size;

    struct timeval st, et;

    char *com_ptr = NULL;
    char* decom_ptr = NULL;

    char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";

    buf_len = strlen(str_buf);
    gettimeofday(&st, NULL);
    while(1) {

        com_ptr = (char *)malloc(buf_len);
        com_size = unishox2_compress_simple(str_buf, buf_len, com_ptr);

        free(com_ptr);
        cnt++;

        gettimeofday(&et, NULL);
        if(et.tv_sec - st.tv_sec >= 10) {
            break;
        }
    }

    printf("ncompress per second:%d timesn", cnt/10);

    cnt = 0;
    com_ptr = (char *)malloc(buf_len);
    com_size = unishox2_compress_simple(str_buf, buf_len, com_ptr);

    gettimeofday(&st, NULL);
    while(1) {

        // decompress length not more than origin buf length
        decom_ptr = (char *)malloc(buf_len + 1);
        decom_size = unishox2_decompress_simple(com_ptr, com_size, decom_ptr);

        // check decompress length
        if(buf_len != decom_size) {
            printf("decom errorn");
        }

        free(decom_ptr);
        cnt++;

        gettimeofday(&et, NULL);
        if(et.tv_sec - st.tv_sec >= 10) {
            break;
        }
    }

    printf("decompress per second:%d timesnn", cnt/10);

    free(com_ptr);
    return 0;
}

執行結果如下：