BITMAP Implementation in C

Dear Reader,

    In this post, i would like to bring you about BIT MAP and its implementation in C used for real time applications

What is BIT MAP?
   Bit Maps are also called as " BIT Array".
   Bit array means that store bits.

Why  BIT MAPS are required?
   Using Bit Array, applications achieve bit-level parallelism in hardware to perform operations quickly.

Some more Info..

Each bit array is mapped to some domain, the bit values can be interpreted as

1. Dark/Light  2. Absent/Present   3. Locked/Unlocked    4. Valid/Invalid

In other words, there are only two possible values.

• 1 bit indicates the value is SET in a number
• 0 bit indicates the value is UNSET in a number

For Bit Maps 

•     OR (|)  is used to set the bit (e.g  n |= (1<<x) )
•     AND (&) is used to clear the bit  (e.g   n &= ~(1<<x))

 How to Implement the Bit Maps?

Step 1:  Create a bit Map Array.
             unsigned char bit_map[2];

Step 2: Calculate the Bit Map array Index and shift index (How many bits needs to shift).
            < If the user gives  bit_position  input starts from 1>
            bit_map_array_index = (bit_position - 1) /8   
            shift_Index = (bit_position - 1)%8

           < If the user gives  bit_position  input starts from 0>
            bit_map_array_index = bit_position /8   
            shift_Index = bit_position %8

Step 3: Set the Bit in the Bit Map using
            bit_map[bit_map_array_index] |= (1<<shift_Index)

Step 4: Clear the Bit in the Bit Map using
            bit_map[bit_map_array_index] &=  ~(1<<shift_Index)

 Please find the below program for Better Understanding of Bit Maps in C.

#include<stdio.h>
#include<stdlib.h>

#define EXIT 100

#define BITMAP_LEN 2
#define BYTE_LEN   8

/* Debug OutPut */
void printTheDebugOutput(unsigned char *bit_array)
{
   int i, j;

   /* Array is 2 bit_array[0] and [1] */
   for (i=0 ; i<BITMAP_LEN; i++)
   {
     /* Bits 0..7 */
     for(j=1; j<=BYTE_LEN; j++)
     {
        if(bit_array[i] & (1 << (j-1)))
        {
           printf("In BIT_MAP[%d] the position of Bit SET : %d\n",
                                   i, j);
        }
     }
   }
}

/*
 *  Main() function
 */
int main()
{

  unsigned int bit_position, setOrUnsetBit, ch;
  unsigned char bit_Map_array_index, shift_index;

  /* Declare Bit Array and intialised to Zero
   * This BIT_MAP is generally assigned to one domain.
   * Here BIT MAP (Array of Bits) are used for Debugging Mechanism
   */
  unsigned char bit_map[BITMAP_LEN] = { 0 };
 
  /* In Bit- Maps , there are two options,
   * either  Set (OR |) or  Unset (AND &) bit.
   */
 do
 {
    /* Here the Max number of bits is 16 ranging from 1..16 */
    printf("Enter the Bit position (bit starts from 1 and Ends at 16) \n");
    scanf("%d", &bit_position); 

    /*
     * Set/Unset the Bit Map indicates which bits you want to enable 
     */
    printf(" Do you want to set/unset the Bit (1 or 0) \n");
    scanf("%d", &setOrUnsetBit);

    /* LOGIC as follows */
    /* Find Out the Index and and as well as Shift Index */

    /* It Give output as 0 or 1 ( for Bit Position 1..16) */
    bit_Map_array_index = (bit_position-1) / 8;

    /* Always give output as 0...7 ( for Bit Position 1..16)*/
    shift_index =  (bit_position-1) % 8;

    printf("The bit_position : %d shift Index : %d\n", bit_position, shift_index);

    /* If set is true */
    if( setOrUnsetBit)
     {        
       /* Set the Bit Array */
       bit_map[bit_Map_array_index] |= 1<<shift_index;                
     }
    else
     { 
        /* Clear the Bit Array */ 
        bit_map[bit_Map_array_index] &= ~(1<<shift_index);        
     }
    printf(" The Bit MAP Array : %d\n", bit_map[bit_Map_array_index]);
    printTheDebugOutput(bit_map);
   
    printf(" Do You want to Continue then Enter any Number"
           "and for Exit then enter 100\n");
    scanf("%d", &ch);

  }while(ch != 100);
 return 0;
}


Please refer in the blog for DEBUG LOG IMPLEMENTATION USING BIT MAP.