set_bit

set_bit Function

The set_bit function sets the bit at position p of the byte x to 1.

uint8_t set_bit(uint8_t x, uint8_t p)
{
    return (x | (1 << p));
}

Explanation

1. Bit Shifting: The expression (1 << p) shifts the number 1 to the left by p positions. This creates a mask with a 1 at the p-th position and 0s elsewhere.

2. Bitwise OR: The bitwise OR operator | combines the original number x with the mask. This sets the bit at position p to 1 while leaving all other bits unchanged.

Example

Let's take an example where x = 5 (binary 00000101) and p = 2.

Step-by-Step Process

1. Initial Value:

   • x = 00000101 (binary)
   • p = 2

2. Create the Mask:

   • 1 << p shifts 1 to the left by 2 positions.
   • 1 << 2 becomes 00000100 (binary).

3. Bitwise OR Operation:

   • Original x: 00000101
   • Mask: 00000100
   • Result of x | (1 << p): 00000101 | 00000100

Bitwise OR Operation

Bit Position	7	6	5	4	3	2	1	0
x	0	0	0	0	0	1	0	1
1 << p	0	0	0	0	0	1	0	0
Result	0	0	0	0	0	1	0	1

The 2-th bit of x is set to 1, resulting in 00000101 which is 5 in decimal.

Another example

x = 00000101  (binary for 5)
p = 2

Step 1: Shift 1 left by 2 positions
1 << 2 = 00000100

Step 2: Perform bitwise OR with x
x       = 00000101
1 << p  = 00000100
----------------
Result  = 00000101

Summary

The set_bit function works by creating a mask with a 1 at the desired bit position and then using the bitwise OR operation to set that bit in the original number.

In our example, setting the 2-th bit of 5 doesn't change the value because the bit was already 1. If it was 0, it would have been set to 1.