How to replace 1 bit of an integer without changing the other neighboring bits?
I want to change 1 bit and keep the same values of the other neighboring bits.
The bit operator shifts left or right, changing the 1-pair 0 bit, but it changes the entire 8-bit sequence. I didn't want that to happen.
As an alternative, I change the integer itself, with this the bit I want is changed.
Please, can anyone help?
Thank you!
2 answers
If we use XOR with 1 gives to exchange a bit:
0 ^ 1 = 1
1 ^ 1 = 0
For example to change a 0 to a 4 we change the 3rd bit.
char a = 0x00;
int bit = 2;
a ^= (1 << bit)
The C language even allows us to make the use of struct and union to be able to directly deeminate the value of one or more bits with the operator =.
This functionality is little used - and in any case, it requires you to define a Union by naming the bits (or fields with different bit sizes).
To change a "generic" bit into a byte, the most common is:
- Create a number with the bit in the right position
- use the "|" ("or" binary) operation to set O bit
This if you want to pass the bit always from 0 to 1. Using the " xor " will always reverse the bit. And if you want to delete a bit, then the process involves creating a mask where the desired bit has the value "0", and applying the operation"&".
We can do a function to set or reset a bit that does this: receive a pointer to the byte to change, the bit position, and the desired value. We create the byte with the bit in "1" in the correct position - (using the operator <<), the from it we create a mask with this bit at zero, and apply the bit with the sent value. In C:
void altera_bit(char *alvo, char posicao, char valor) {
char mascara = ~(1 << posicao);
*alvo = (*alvo & mascara) | (valor << posicao);
}