LZW算法中字符编码

shigw001

1. #define BITS_PER_BYTE 8
   
2. #define INITIAL_CODE_WIDTH 9
   
3. #define Increment 3
   
4. #define BITS 12
   
5. 
   
6. unsigned int input_code(FILE *input)
   
7. {
   
8.     unsigned int return_value;
   
9.     static int input_bit_count=0;
   
10.     static unsigned long input_bit_buffer=0L;
    
11. 
    
12.     while (input_bit_count <= 24)
    
13.     {
    
14.         input_bit_buffer |=
    
15.         (unsigned long) getc(input) << (24-input_bit_count);
    
16.         input_bit_count += 8;
    
17.     }
    
18.     return_value=input_bit_buffer >> (32-BITS);
    
19.     input_bit_buffer <<= BITS;
    
20.     input_bit_count -= BITS;
    
21.     return(return_value);
    
22. }
    
23. 
    
24. void output_code(FILE *output,unsigned int code)
    
25. {
    
26.     static int output_bit_count=0;
    
27.     static unsigned long output_bit_buffer=0L;
    
28. 
    
29.     output_bit_buffer |= (unsigned long) code << (32-BITS-output_bit_count);
    
30.     output_bit_count += BITS;
    
31.     while (output_bit_count >= 8)
    
32.     {
    
33.         putc(output_bit_buffer >> 24,output);
    
34.         output_bit_buffer <<= 8;
    
35.         output_bit_count -= 8;
    
36.     }
    
37. }

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最近在看LZW算法，看到有这么两个函数，一个是将字符编码写入流， 一个从流中读取， 一直不是很明白两个函数的操作。请达人讲解下