64 lines
1.3 KiB
Markdown
64 lines
1.3 KiB
Markdown
---
|
|
title: "Bit magic in C (and C++)"
|
|
subtitle: "Tips and trick for embedded C/C++"
|
|
summary: "Tips and trick for embedded C/C++"
|
|
date: 2020-06-13T19:01:19+02:00
|
|
highlight: true
|
|
---
|
|
|
|
# Set a bit
|
|
```c
|
|
// Set one bit high at position "bit" in input and store to output
|
|
output = input | (1 << bit);
|
|
// Shorthand
|
|
variable |= (1 << bit);
|
|
// Multiple bits
|
|
variable |= (0b101 << bit);
|
|
```
|
|
|
|
# Clear a bit
|
|
```c
|
|
// Clear one bit high at position "bit" in input and store to output
|
|
output = input & ~(1 << bit);
|
|
// Shorthand
|
|
variable &= ~(1 << bit);
|
|
// Multiple bits
|
|
variable &= ~(0b101 << bit);
|
|
```
|
|
|
|
# Toggle a bit
|
|
```c
|
|
// Clear one bit high at position "bit" in input and store to output
|
|
output = x ^ (1 << bit);
|
|
// Shorthand
|
|
variable ^= (1 << bit);
|
|
// Multiple bits
|
|
variable ^= (0b101 << bit);
|
|
```
|
|
|
|
# Math
|
|
```c
|
|
// Division using bitshift
|
|
output = input >> 1; // Divide by 2
|
|
output = input >> 2; // Divide by 4
|
|
output = input >> 3; // Divide by 8
|
|
// Multiply using bitshifting
|
|
output = input << 1; // Multiply by 2
|
|
output = input << 2; // Multiply by 4
|
|
output = input << 3; // Multiply by 8
|
|
```
|
|
|
|
# Set X number of bits high.
|
|
```c
|
|
output = (0b1 << X) -1;
|
|
```
|
|
|
|
# Miscellaneous
|
|
```c
|
|
// Check if number is ODD
|
|
if( (num & 1) == 1) {};
|
|
// Flip signed integer
|
|
num = ~num + 1;
|
|
// Power of two
|
|
num > 0 && (num & (num - 1)) == 0;
|
|
``` |