Ex1/src/circuit.rs

use crate::{gate::Gate, gate_type::GateType};


#[derive(Debug, Clone)]
pub struct Circuit {
    pub input_bits: Vec<bool>, // Input wires
    pub gates: Vec<Gate>,      // All gates
}

impl Circuit {
    pub fn eval(self) -> bool {
        let mut evaluated_gates = vec!();

        for gate in self.gates {
            let result = gate.eval(&self.input_bits, &evaluated_gates);
            evaluated_gates.push(result);
        }

        match evaluated_gates.pop() {
            Some(result) => result,
            None => panic!("Bruh moment")
        } 
    }

    /*
        This method should create a circuit that outputs 1 if the first number A (encoded in the first n
        bits) is greater than the second number B (encoded in the next n bits) .
    */
    pub fn compare_n_bit_numbers(input_bits: Vec<bool>, n: usize) -> Self {
        if input_bits.len() < 2*n {
            panic!("Expected input_bits to be of at least length {}, but it was {}", 2*n, input_bits.len())
        }

        /*
            base case n=1: 1-bit: 
            
                A B | A > B
                -----------
                0 0 |   0
                0 1 |   0
                1 0 |   1
                1 1 |   0

            n+1 case: 2-bit:

                A1 A0  B1 B0  | A > B | (A1 > B1) || ((A1 == B1) && (A0 > B0))
                ----------------------|------------------------------------
                0  0   0  0   |   0   |            0
                0  0   0  1   |   0   |            0
                0  0   1  0   |   0   |            0
                0  0   1  1   |   0   |            0
                0  1   0  0   |   1   |            1
                0  1   0  1   |   0   |            0
                0  1   1  0   |   0   |            0
                0  1   1  1   |   1   |            1
                1  0   0  0   |   1   |            1
                1  0   0  1   |   1   |            1
                1  0   1  0   |   0   |            0
                1  0   1  1   |   0   |            0
                1  1   0  0   |   1   |            1
                1  1   0  1   |   1   |            1
                1  1   1  0   |   1   |            1
                1  1   1  1   |   0   |            0

            The inductive pattern should become apparent now. 
            For illustration here's the case for n=4, which should show the 
            recursive characteristics of the formula. 

            (A3 > B3) || 
            ((A3 == B3) && (A2 > B2)) || 
            ((A3 == B3) && (A2 == B2) && (A1 > B1)) ||
            ((A3 == B3) && (A2 == B2) && (A1 == B1)) && (A0 > B0))

        */

        let gates = create_n_bit_comparator_gates(n);
        return Circuit { input_bits, gates }
    }
}


fn create_n_bit_comparator_gates(n: usize) -> Vec<Gate>{
    let mut indices: Vec<usize> = vec![0; n];
    let mut all_gates: Vec<Gate> = vec!();
    let mut and_gate_indices: Vec<usize> = vec!();
    
    

    rec_n_bit_comperator_gates(0, n, &mut all_gates, &mut and_gate_indices, &mut indices, );

    // the OR spanning all ANDs
    let or_gate = Gate::new( GateType::Or, and_gate_indices, vec!());
    
    all_gates.push(or_gate);

    return all_gates;
}

fn rec_n_bit_comperator_gates(curr: usize, max: usize, all_gates: &mut Vec<Gate>, and_gate_incides: &mut Vec<usize>, indices: &mut Vec<usize>){
    // Incrementing gate index
    let a_curr_gt_b_curr_gate_index = all_gates.len();

    // Gate(A_current > B_current)
    let a_curr_gt_b_curr_gate = Gate::new(GateType::Bigger, vec!(), vec!(curr, curr+max));

    // A_current>B_current
    //print!("   ( ({}) ", format!("{} > {}", format!("A{}", max-1-curr), format!("B{}", max-1-curr)));

    all_gates.push(a_curr_gt_b_curr_gate);

    let mut this_recursion_gate_indices: Vec<usize> = vec!(a_curr_gt_b_curr_gate_index);

    for i in 0..curr {
        let key = max-1-i;
        if i == curr-1 {
            // Gate(A_current > B_current)
            let a_i_eq_b_i_gate = Gate::new(GateType::Equal, vec!(), vec!(i, i+max));
            let a_curr_gt_b_curr_gate_index = all_gates.len();
            indices[key] = a_curr_gt_b_curr_gate_index;
            all_gates.push(a_i_eq_b_i_gate);
        }
        let eq_gate_index = indices[key];

        //print!("&& ({}) ", format!("{} = {}", format!("A{}", key), format!("B{}", key)));

        // Index of this equality gate
        this_recursion_gate_indices.push(eq_gate_index);
    }

    let and_curr_index = all_gates.len(); 
    let and_curr_gate = Gate::new(GateType::And, this_recursion_gate_indices, vec!());

    all_gates.push(and_curr_gate);
    and_gate_incides.push(and_curr_index);

    if curr+1 == max {
        //println!(")");
        return;
    }
    //println!(") ||");
    return rec_n_bit_comperator_gates(curr+1, max, all_gates, and_gate_incides, indices);
}