字符串压缩（三）之短字符串压缩-创新互联

一、通用算法的短字符压缩

开门见山，我们使用一段比较短的文本：Narrator: It is raining today. So, Peppa and George cannot  play outside.Peppa: Daddy, it's stopped raining.

使用ZSTD与LZ4分别压缩一下上面这段短文本。下面分别是它们的压缩结果。

ZSTD：

LZ4：

对短文本的压缩，zstd的压缩率很低，lz4压缩后的文本长度尽然超过了原有字符串的长度。这是为什么？说实话在这之前我也没想到。

引用两位大佬的名言：

Are you ok?  

What's your problem?

二、短字符串压缩

从上面的结果可以得知，任何压缩算法都有它的使用场景，并不是所有长度的字符串都适合被某种算法压缩。一般原因是通用压缩算法维护了被压缩字符串的，用于字符串还原的相关数据结构，而这些数据结构的长度超过了被压缩短字符串的自身长度。

那么问题来了，“我真的有压缩短字符串的需求，我想体验压缩的极致感，怎么办？”。

短字符压缩算法它来了。这里挑选了3种比较优异的短字符压缩算法，分别是smaz，shoco，以及压轴的unisox2。跟前两章一样，还是从压缩率，压缩和解压缩性能的角度，一起看看他们在短字符压缩场景的各自表现吧。

（1）Smaz

1、Smaz的压缩和解压缩

1 #include2 #include3 #include4 #include "smaz.h"
 5 
 6 using namespace std;
 7 
 8 int main()
 9 {
10     int buf_len;
11     int com_size;
12     int decom_size;
13     
14     char com_buf[4096] = {0};
15     char decom_buf[4096] = {0};
16 
17     char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";
18 
19     buf_len = strlen(str_buf);
20     com_size = smaz_compress(str_buf, buf_len, com_buf, 4096);
21     
22     cout<< "text size:"<< buf_len<< endl;
23     cout<< "compress text size:"<< com_size<< endl;
24     cout<< "compress ratio:"<< (float)buf_len / (float)com_size<< endl<< endl;
25 
26     decom_size = smaz_decompress(com_buf, com_size, decom_buf, 4096);
27     cout<< "decompress text size:"<< decom_size<< endl;
28 
29     if(strncmp(str_buf, decom_buf, buf_len)) {
30         cout<< "decompress text is not equal to source text"<< endl;
31     }
32 
33     return 0;
34 }

执行结果如下：

通过smaz压缩后的短字符串长度为77，和源字符串相比，减少了30Byte。

2、Smaz的压缩和解压缩性能

1 #include2 #include3 #include4 #include5 #include "smaz.h"
 6 
 7 using namespace std;
 8 
 9 int main()
10 {
11     int cnt = 0;
12     int buf_len;
13     int com_size;
14     int decom_size;
15 
16     timeval st, et;
17     
18     char *com_ptr = NULL;
19     char* decom_ptr = NULL;
20 
21     char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";
22 
23     buf_len = strlen(str_buf);
24     gettimeofday(&st, NULL);
25     while(1) {
26         
27         com_ptr = (char *)malloc(buf_len);
28         com_size = smaz_compress(str_buf, buf_len, com_ptr, buf_len);
29 
30         free(com_ptr);
31         cnt++;
32         
33         gettimeofday(&et, NULL);
34         if(et.tv_sec - st.tv_sec >= 10) {
35             break;
36         }
37     }
38 
39     cout<< endl<<"compress per second:"<< cnt/10<< " times"<< endl;
40 
41     cnt = 0;
42     com_ptr = (char *)malloc(buf_len);
43     com_size = smaz_compress(str_buf, buf_len, com_ptr, buf_len);
44     
45     gettimeofday(&st, NULL);
46     while(1) {
47 
48         // decompress length not more than origin buf length
49         decom_ptr = (char *)malloc(buf_len + 1);
50         decom_size = smaz_decompress(com_ptr, com_size, decom_ptr, buf_len + 1);
51 
52         // check decompress length
53         if(buf_len != decom_size) {
54             cout<< "decom error"<< endl;
55         }
56         
57         free(decom_ptr);
58         cnt++;
59         
60         gettimeofday(&et, NULL);
61         if(et.tv_sec - st.tv_sec >= 10) {
62             break;
63         }
64     }
65 
66     cout<< "decompress per second:"<< cnt/10<< " times"<< endl<< endl;
67     
68     free(com_ptr);
69     return 0;
70 }

结果如何？

压缩性能在40w条/S，解压在百万级，好像还不错哈！

（2）Shoco

1、Shoco的压缩和解压缩

1 #include2 #include3 #include4 #include "shoco.h"
 5 
 6 using namespace std;
 7 
 8 int main()
 9 {
10     int buf_len;
11     int com_size;
12     int decom_size;
13     
14     char com_buf[4096] = {0};
15     char decom_buf[4096] = {0};
16 
17     char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";
18 
19     buf_len = strlen(str_buf);
20     com_size = shoco_compress(str_buf, buf_len, com_buf, 4096);
21     
22     cout<< "text size:"<< buf_len<< endl;
23     cout<< "compress text size:"<< com_size<< endl;
24     cout<< "compress ratio:"<< (float)buf_len / (float)com_size<< endl<< endl;
25 
26     decom_size = shoco_decompress(com_buf, com_size, decom_buf, 4096);
27     cout<< "decompress text size:"<< decom_size<< endl;
28 
29     if(strncmp(str_buf, decom_buf, buf_len)) {
30         cout<< "decompress text is not equal to source text"<< endl;
31     }
32 
33     return 0;
34 }

执行结果如下：

通过shoco压缩后的短字符串长度为86，和源字符串相比，减少了21Byte。压缩率比smaz要低。

2、Shoco的压缩和解压缩性能

1 #include2 #include3 #include4 #include5 #include "shoco.h"
 6 
 7 using namespace std;
 8 
 9 int main()
10 {
11     int cnt = 0;
12     int buf_len;
13     int com_size;
14     int decom_size;
15 
16     timeval st, et;
17     
18     char *com_ptr = NULL;
19     char* decom_ptr = NULL;
20 
21     char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";
22 
23     buf_len = strlen(str_buf);
24     gettimeofday(&st, NULL);
25     while(1) {
26         
27         com_ptr = (char *)malloc(buf_len);
28         com_size = shoco_compress(str_buf, buf_len, com_ptr, buf_len);
29 
30         free(com_ptr);
31         cnt++;
32         
33         gettimeofday(&et, NULL);
34         if(et.tv_sec - st.tv_sec >= 10) {
35             break;
36         }
37     }
38 
39     cout<< endl<<"compress per second:"<< cnt/10<< " times"<< endl;
40 
41     cnt = 0;
42     com_ptr = (char *)malloc(buf_len);
43     com_size = shoco_compress(str_buf, buf_len, com_ptr, buf_len);
44     
45     gettimeofday(&st, NULL);
46     while(1) {
47 
48         // decompress length not more than origin buf length
49         decom_ptr = (char *)malloc(buf_len + 1);
50         decom_size = shoco_decompress(com_ptr, com_size, decom_ptr, buf_len + 1);
51 
52         // check decompress length
53         if(buf_len != decom_size) {
54             cout<< "decom error"<< endl;
55         }
56         
57         free(decom_ptr);
58         cnt++;
59         
60         gettimeofday(&et, NULL);
61         if(et.tv_sec - st.tv_sec >= 10) {
62             break;
63         }
64     }
65 
66     cout<< "decompress per second:"<< cnt/10<< " times"<< endl<< endl;
67     
68     free(com_ptr);
69     return 0;
70 }

执行结果如何呢？

holy shit！压缩和解压缩居然都达到了惊人的百万级。就像算法作者们自己说的一样：“在长字符串压缩领域，shoco不想与通用压缩算法竞争，我们的优势是短字符的快速压缩，虽然压缩率很烂！”。这样说，好像也没毛病。

（3）Unisox2

我们再来看看unisox2呢。

1、Unisox2的压缩和解压缩

1 #include2 #include3 #include "unishox2.h"
 4 
 5 int main()
 6 {
 7     int buf_len;
 8     int com_size;
 9     int decom_size;
10     
11     char com_buf[4096] = {0};
12     char decom_buf[4096] = {0};
13     
14     char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";
15     
16     buf_len = strlen(str_buf);
17     com_size = unishox2_compress_simple(str_buf, buf_len, com_buf);
18 
19     printf("text size:%d\n", buf_len);
20     printf("compress text size:%d\n", com_size);
21     printf("compress ratio:%f\n\n", (float)buf_len / (float)com_size);
22     
23     decom_size = unishox2_decompress_simple(com_buf, com_size, decom_buf);
24 
25     printf("decompress text size:%d\n", decom_size);
26 
27     if(strncmp(str_buf, decom_buf, buf_len)) {
28         printf("decompress text is not equal to source text\n");
29     }
30 
31     return 0;
32 }

结果如下：

通过Unisox2压缩后的短字符串长度为67，和源字符串相比，减少了40Byte，相当于是打了6折啊！不错不错。

2、Unisox2的压缩和解压缩性能

Unisox2的压缩能力目前来看是三者中最好的，如果他的压缩和解压性能也不错的话，那就真的就比较完美了。再一起看看Unisox2的压缩和解压性能吧！

1 #include2 #include3 #include4 #include5 #include "unishox2.h"
 6 
 7 int main()
 8 {
 9     int cnt = 0;
10     int buf_len;
11     int com_size;
12     int decom_size;
13 
14     struct timeval st, et;
15     
16     char *com_ptr = NULL;
17     char* decom_ptr = NULL;
18 
19     char str_buf[1024] = "Narrator: It is raining today. So, Peppa and George cannot play outside.Peppa: Daddy, it's stopped raining.";
20 
21     buf_len = strlen(str_buf);
22     gettimeofday(&st, NULL);
23     while(1) {
24         
25         com_ptr = (char *)malloc(buf_len);
26         com_size = unishox2_compress_simple(str_buf, buf_len, com_ptr);
27 
28         free(com_ptr);
29         cnt++;
30         
31         gettimeofday(&et, NULL);
32         if(et.tv_sec - st.tv_sec >= 10) {
33             break;
34         }
35     }
36 
37     printf("\ncompress per second:%d times\n", cnt/10);
38 
39     cnt = 0;
40     com_ptr = (char *)malloc(buf_len);
41     com_size = unishox2_compress_simple(str_buf, buf_len, com_ptr);
42     
43     gettimeofday(&st, NULL);
44     while(1) {
45 
46         // decompress length not more than origin buf length
47         decom_ptr = (char *)malloc(buf_len + 1);
48         decom_size = unishox2_decompress_simple(com_ptr, com_size, decom_ptr);
49 
50         // check decompress length
51         if(buf_len != decom_size) {
52             printf("decom error\n");
53         }
54         
55         free(decom_ptr);
56         cnt++;
57         
58         gettimeofday(&et, NULL);
59         if(et.tv_sec - st.tv_sec >= 10) {
60             break;
61         }
62     }
63 
64     printf("decompress per second:%d times\n\n", cnt/10);
65     
66     free(com_ptr);
67     return 0;
68 }

执行结果如下：

事与愿违，Unisox2虽然有三个算法中最好的压缩率，可是却也拥有最差的压缩和解压性能。

三、总结

本篇分享了smaz，shoco，unisox2三种短字符串压缩算法，分别探索了它们各自的压缩率与压缩和解压缩性能，结果如下表所示。

表1

shoco的压缩率最低，但是拥有最高的压缩和解压速率；smaz居中；unisox2拥有最高的压缩率，可是它的压缩和解压性能最低。

结论与前两章有关长字符串压缩的分析不谋而合：拥有高压缩率，就会损失自身的压缩性能，两者不可兼得。

实际使用还是看自身需求和环境吧。如果适当压缩就好，那就可以选用shoco，毕竟性能高；想要节约更多的空间，那就选择smaz或者unisox2。

好了，字符串压缩系列的分享就到此为止了，如果对你有些许帮助，还请各位技术爱好者登录点赞呀，谢谢！

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