Calculator Contract

This Compact contract implements a simple calculator. It offers demonstration of the following features:

• Witness function
• On-chain verification of off-chain compute

Notice that divMod only has the declaration of the function signature. Its logic is implemented in the Typescript frontend and is unknown to contract, though we can enforce expected execution through assert statements in divide.

pragma language_version 0.22;

export ledger result: Uint<16>;

export circuit add(num1: Uint<16>, num2: Uint<16>): [] {
    result = disclose(num1 + num2 as Uint<16>);
}

export circuit subtract(num1: Uint<16>, num2: Uint<16>): [] {
    result = disclose(num1 - num2 as Uint<16>);
}

export circuit multiply(num1: Uint<16>, num2: Uint<16>): [] {
    result = disclose(num1 * num2 as Uint<16>);
}

export circuit square(num1: Uint<16>): [] {
    result = disclose(num1 * num1 as Uint<16>);
}

// declare an off-chain function expected to divide two numbers
witness divMod(num1: Uint<16>, num2: Uint<16>): [Uint<16>, Uint<16>];

// enforce correct logic on-chain for off-chain logic in divMod
circuit divide(num1: Uint<16>, num2: Uint<16>): Uint<16> {
    const [quo, rem] = divMod(num1, num2);
    assert(rem < num2 && quo * num2 + rem == num1, "incorrect division");
    return quo;
}