C語言實現短字符串壓縮的三種方法詳解

前言

上一篇探索瞭LZ4的壓縮和解壓性能,以及對LZ4和ZSTD的壓縮、解壓性能進行瞭橫向對比。文末的最後也給瞭一個彩蛋:任意長度的字符串都可以被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、通用算法的短字符壓縮

開門見山,我們使用一段比較短的文本: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本。下面分別是它們的壓縮結果。

ZSTD:

LZ4:

對短文本的壓縮,zstd的壓縮率很低,lz4壓縮後的文本長度盡然超過瞭原有字符串的長度。這是為什麼?說實話在這之前我也沒想到。

引用兩位大佬的名言:

Are you ok?  

What's your problem?

二、短字符串壓縮

從上面的結果可以得知,任何壓縮算法都有它的使用場景,並不是所有長度的字符串都適合被某種算法壓縮。一般原因是通用壓縮算法維護瞭被壓縮字符串的,用於字符串還原的相關數據結構,而這些數據結構的長度超過瞭被壓縮短字符串的自身長度。

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

短字符壓縮算法它來瞭。這裡挑選瞭3種比較優異的短字符壓縮算法,分別是smaz,shoco,以及壓軸的unisox2。跟前兩章一樣,還是從壓縮率,壓縮和解壓縮性能的角度,一起看看他們在短字符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壓縮後的短字符串長度為77,和源字符串相比,減少瞭30Byte。

2、Smaz的壓縮和解壓縮性能

#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?

壓縮性能在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壓縮後的短字符串長度為86,和源字符串相比,減少瞭21Byte。壓縮率比smaz要低。

 2、Shoco的壓縮和解壓縮性能

#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瞭驚人的百萬級。就像算法作者們自己說的一樣:“在長字符串壓縮領域,shoco不想與通用壓縮算法競爭,我們的優勢是短字符的快速壓縮,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:%d\n", buf_len);
    printf("compress text size:%d\n", com_size);
    printf("compress ratio:%f\n\n", (float)buf_len / (float)com_size);

    decom_size = unishox2_decompress_simple(com_buf, com_size, decom_buf);

    printf("decompress text size:%d\n", decom_size);

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

    return 0;
}

結果如下:

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

 2、Unisox2的壓縮和解壓縮性能

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性能也不錯的話,那就真的就比較完美瞭。再一起看看Unisox2的壓縮和解壓性能吧!

#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 times\n", 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 error\n");
        }

        free(decom_ptr);
        cnt++;

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

    printf("decompress per second:%d times\n\n", cnt/10);

    free(com_ptr);
    return 0;
}

執行結果如下:

事與願違,Unisox2雖然有三個算法中最好的壓縮率,可是卻也擁有最差的壓縮和解壓性能。跟前兩章分析的不謀而合:有高壓縮率,就會損失自身的壓縮性能,兩者不可兼得。

三、總結

本篇分享瞭smaz,shoco,unisox2三種短字符串壓縮算法,分別探索瞭它們各自的壓縮率與壓縮和解壓縮性能,結果如下表所示。

表1

shoco的壓縮率最低,但是擁有最高的壓縮和解壓速率;smaz居中;unisox2擁有最高的壓縮率,可是它的壓縮和解壓性能最低。

結論與前兩章有關長字符串壓縮的分析不謀而合:擁有高壓縮率,就會損失自身的壓縮性能,兩者不可兼得。

實際使用還是看自身需求和環境吧。如果適當壓縮就好,那就可以選用shoco,畢竟性能高;想要節約更多的空間,那就選擇smaz或者unisox2。

到此這篇關於C語言實現短字符串壓縮的三種方法詳解的文章就介紹到這瞭,更多相關C語言短字符串壓縮內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet!

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