If vs Else If performance test - Cairo

[danilowhk]

Comparing Multiple Consecutive if vs if-else Statements: A Benchmark

Introduction

This report compares the gas cost of using multiple consecutive if statements versus using if-else statements. The tests were conducted considering 20 conditions, utilizing scarb 0.6.0-alpha.2 and cairo 2.1.0-rc2.

Methodology

The benchmarks were conducted under the following configurations:

• Language: Cairo
• Version: scarb 0.6.0-alpha.2, cairo 2.1.0-rc2
• Conditions: 20 different conditions were evaluated
• Metrics: Gas consumption

Overall Result

The comparison between consecutive 20 consecutive if statements and 20 consecutive if-else statements highlight a significant difference in gas consumption:

| Approach                | Gas Consumption |
|-------------------------|-----------------|
| Consecutive `if`        | 7620           |
| Consecutive `if-else`   | 7620           |

Test with Consecutive if Statements

Description

This approach uses consecutive if statements, where each condition is evaluated independently.

Code

fn test_if_function(a: felt252) -> felt252{
    if a == 1 {
        return a;
    }
    if a == 2 {
        return a;
    }
    if a == 3 {
        return a;
    }
    if a == 4 {
        return a;
    }
    if a == 5 {
        return a;
    }
    if a == 6 {
        return a;
    }
    if a == 7 {
        return a;
    }
    if a == 8 {
        return a;
    }
    if a == 9 {
        return a;
    }
    if a == 10 {
        return a;
    }

    if a == 11 {
        return a;
    }
    if a == 12 {
        return a;
    }
    if a == 13 {
        return a;
    }
    if a == 14 {
        return a;
    }
    if a == 15 {
        return a;
    }
    if a == 16 {
        return a;
    }
    if a == 17 {
        return a;
    }
    if a == 18 {
        return a;
    }
    if a == 19 {
        return a;
    }
    if a == 20 {
        return a;
    }
    return a;

}


#[test]
#[available_gas(1000000)]
fn test_if() {
    let x = testing::get_available_gas();
    gas::withdraw_gas().unwrap();
    let a = 20;
    let value = test_if_function(a);

    (x - testing::get_available_gas()).print();
}

Result

Gas consumption for this test was 7620.

Test with if-else Statements

Description

This approach uses if-else statements, evaluating conditions sequentially and exiting when a true condition is met.

Code

fn test_if_else_function(a: felt252) -> felt252 {

    if a == 1 {
        return a;
    } else if a == 2 {
        return a;
    } else if a == 3 {
        return a;
    } else if a == 4 {
        return a;
    } else if a == 5 {
        return a;
    } else if a == 6 {
        return a;
    } else if a == 7 {
        return a;
    } else if a == 8 {
        return a;
    } else if a == 9 {
        return a;
    } else if a == 10 {
        return a;
    } else if a == 11 {
        return a;
    } else if a == 12 {
        return a;
    } else if a == 13 {
        return a;
    } else if a == 14 {
        return a;
    } else if a == 15 {
        return a;
    } else if a == 16 {
        return a;
    } else if a == 17 {
        return a;
    } else if a == 18 {
        return a;
    } else if a == 19 {
        return a;
    } else if a == 20 {
        return a;
    }
    return a;

}

#[test]
#[available_gas(1000000)]
fn test_if_else() {
    let x = testing::get_available_gas();

    gas::withdraw_gas().unwrap();
    let a = 20;
    let value = test_if_else_function(a);

    (x - testing::get_available_gas()).print();
}

Result

Gas consumption for this test was 7620.

Conclusion

The tests indicate that using if-else costs the same amount of steps compared to consecutive ifs.

Appendix:

Versions used:

scarb: 0.6.0-alpha.2 (4b4d5411b 2023-07-25)
cairo: 2.1.0-rc2 (https://crates.io/crates/cairo-lang-compiler/2.1.0-rc2)

[enitrat]

would that make a difference if you had return statements in each branch? Here, you're not really comparing two similar behaviors.