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Chapter 03

Commonly used bit-manipulation functions

Page 12

Some Questions on Bit Manipulation

Question: Create a "fence" of ones

Need of such function: For example if there is a byte:
unsigned char byte = 0b11000011;

and it is required to SET multiple (continuous) bits.
Say, Bit number 2,3,4,5 are to be set.

            Bit number 76543210
                       |||||||| 
                       VVVVVVVV
Initially     byte = 0b10000001
Modified      byte = 0b10111101

One way of doing this is:

byte = byte |   (1 << 0x05) |  (1 << 0x04)  | (1 << 0x03) | (1 << 0x02)  ;

Another way of doing this is to use a "fence" of ones:

mask = 0b00111100   ;
byte = byte | mask  ;

Write a Method (WAM) which returns a "mask" in which bits from i to j are SET
Example if i=2 and j=5 the return value (nammed as mask) will be:

                         j  i
                         |  |
                         V  V
            Bit number 76543210
                       |||||||| 
                       VVVVVVVV
              mask = 0b00111100   <---- Return Value

The function prototype is given below:

unsigned char getFence(unsigned char i, unsigned char j)
{
  unsigned char mask;




  return mask;
}

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