Bit manipulation in Rust

bits.rs

fn main() {
    // format a number in two’s complement representation
    let a: i8 = -1;
    assert_eq!(format!("{:b}", a), "11111111");
    
    // concatenate 3 bit slices
    let b: i8 = (0b10 << 4) + (0b10 << 2) + (0b10);
    assert_eq!(b, 0b101010);
    
    // get bit at index 5 (counting from right)
    let index = 5;
    let c: bool = (0b101010 >> index) & 1 == 1;
    assert_eq!(c, true);
    
    // get a bit slice (indices counting from right)
    let (start, end) = (3, 6);
    let mask = !(-1 << (end - start));
    let d: i8 = (0b101010 >> start) & mask;
    assert_eq!(d, 0b101);
    
}

Another interesting approach to extract bit (from Nand2Tetris discussions):

1. turn off every bit except the one we want to extract
2. check if the result is zero or not

let masks = [
  0000_0001,
  0000_0010,
  0000_0100,
  ...
];

x & masks[i] == 0