Program for putting bits into buffer. This is useful in compression of data, avoide wastage of bits. This program will work for any 32-bits integers.

1:  /******************************************************************************  
2:   *         Include Files  
3:   * ***************************************************************************/  
4:  #include <stdio.h>  
5:  #include <stdlib.h>  
6:  #include <string.h>  
7:  /******************************************************************************  
8:   *         Macros  
9:   * ***************************************************************************/  
10:  #define UINT_64 unsigned long long int  
11:  #define UCHAR unsigned char  
12:  #define OCTET 8  
13:  /******************************************************************************  
14:   *         Global Variables  
15:   * ***************************************************************************/  
16:  /*  
17:   * Remaining Bits give information about empty bits left in one octet  
18:   */  
19:  static int remaining_bits = 8;  
20:  /*  
21:   * Global Index for Octet shifting  
22:   */  
23:  static int idx;  
24:  /*  
25:   * Offset for last set bit from LSB  
26:   */  
27:  static int offset = 0;  
28:  /******************************************************************************  
29:   * This function used to calculate offset length for given Decimal number  
30:   ******************************************************************************/  
31:  int find_offset(UINT_64 num)  
32:  {  
33:    int offset = 0;  
34:    UINT_64 mask = 1<<31;  
35:    while(mask)  
36:    {  
37:      if (num & mask)  
38:      {  
39:        return (32-offset);  
40:      }  
41:      offset++;  
42:      mask >>= 1;  
43:    }  
44:    return 0;  
45:  }  
46:  /*******************************************************************************  
47:   * This function used to fill bits into 2MB buffer  
48:   * ****************************************************************************/  
49:  void put_bits(UCHAR *buf, UINT_64 num)  
50:  {  
51:    int temp = 0;  
52:    /*  
53:     * Checking For OFFSET length  
54:     */  
55:    if ( offset < OCTET )  
56:    {  
57:      /*  
58:       * OFFSET Less than an OCTET means bit patter will fit into single index  
59:       */  
60:      if ( offset < remaining_bits )  
61:      {  
62:        remaining_bits -= offset;  
63:        *(buf + idx) |= num << remaining_bits;  
64:      } else {  
65:        /*  
66:         * This condition executes when bit patter is less than one octet  
67:         * but it entire octet is not available  
68:         */  
69:        *(buf + idx) |= num >> (offset - remaining_bits);  
70:        idx++;  
71:        temp = offset - remaining_bits;  
72:        *(buf + idx) |= num << (OCTET - temp);  
73:        remaining_bits = OCTET - temp;  
74:      }  
75:      return;  
76:    } else {  
77:      /*  
78:       * This condition executes when offset is larger than one octet  
79:       */  
80:      if ( remaining_bits < OCTET)  
81:      {  
82:        /*  
83:         * If last octet is not filled completely, this condition will   
84:         * execute  
85:         */  
86:        offset -= remaining_bits;  
87:        *(buf + idx) |= num >> offset;  
88:        idx++;  
89:        remaining_bits = OCTET;  
90:        if ( offset > 0)  
91:        {  
92:          /*  
93:           * If still offset is there, then start filling form begining  
94:           */  
95:          put_bits(buf,num);  
96:        }  
97:      } else {  
98:        /*  
99:         * This condition will execute when offset is larger than one octet  
100:         */  
101:        *(buf + idx) |= num >> (offset - OCTET);  
102:        idx++;  
103:        offset -= OCTET;  
104:        /*  
105:         * Continue with patter filling process if still offset is still  
106:         * there  
107:         */  
108:        put_bits(buf,num);  
109:      }  
110:    }  
111:  }  
112:  /******************************************************************************  
113:   * Main function  
114:   * ****************************************************************************/  
115:  main()  
116:  {  
117:    int i=0;  
118:    UINT_64 num = 0;  
119:    UCHAR *buff = NULL;  
120:    buff = (char *)malloc(2*1024*1024*sizeof(char));  
121:    if ( NULL == buff)  
122:    {  
123:      printf("failed to allocate memory\n");  
124:      exit(1);  
125:    }  
126:    memset(buff,0,2*1024*1024*sizeof(char));  
127:    do {  
128:      printf("\nEnter any Number or Zero to exit:");  
129:      scanf("%lld",&num);  
130:      /*  
131:       * Finding Last Enabled bit position from LSB  
132:       */  
133:      offset = find_offset(num);  
134:      /*  
135:       * Putting Bit patter into Buffer  
136:       */  
137:      put_bits(buff,num);  
138:      /*  
139:       * Display buffer status  
140:       */  
141:      for (i = 0; i <= idx; i++)  
142:      {  
143:        printf("%4X", buff[i]);  
144:      }  
145:    }while(num != 0);  
146:    printf("\n");  
147:  }  
148:  /******************************* End of File *********************************/