feat(MemcpyEnterScope): enters a new scope for the memory copy operaton with a specified length

[Alvarodb]

resolves #250

[MaksymMalicki]

Thank you for you contribution! If you resolve the the len as Felt and load it to the scope, you can try and write some unit tests, which check the insides of the scope. Write on Telegram if you have any problems 😁

[Alvarodb]

Thank you for you contribution! If you resolve the the len as Felt and load it to the scope, you can try and write some unit tests, which check the insides of the scope. Write on Telegram if you have any problems 😁

Thank you for all the help! I will work on the unit tests.

[Alvarodb]

unit test added for the hint :)

[MaksymMalicki]

One nitpick left, other than that, looks good to me. Good job! 😎
@cicr99 final look?

[MaksymMalicki]

Okey, you need to lint is as well using gofmt -w . or golangci-lint run

[Alvarodb]

Okey, you need to lint is as well using gofmt -w . or golangci-lint run

Oh sure, fixed

[Alvarodb]

One nitpick left, other than that, looks good to me. Good job! 😎 @cicr99 final look?

I think everything is fixed now guys, thank you very much! Let me know if any issues.

[TAdev0]

LGTM ! waiting for final review @rodrigo-pino @chee-chyuan @MaksymMalicki @har777 and we're good to go :)

[TAdev0]

@Alvarodb will compare the result of your hint with the result produced by the python VM today to be 100% sure and then we're good !

[Alvarodb]

@Alvarodb will compare the result of your hint with the result produced by the python VM today to be 100% sure and then we're good !

Ok, sounds good! Thank you @TAdev0

[TAdev0]

@Alvarodb i just tested your hint. Well, there is not much to test actually. The len variable is simply extracted and passed when entering a new scope, so that the new scope contains len as the only key, before copying memory from a location to another.

I used this cairo file that i ran on the python VM :

from starkware.cairo.common.alloc import alloc
from starkware.cairo.common.math import assert_not_zero

// Copies len field elements from src to dst.
func memcpy(dst: felt*, src: felt*, len) {
    struct LoopFrame {
        dst: felt*,
        src: felt*,
    }

    if (len == 0) {
        return ();
    }

    %{ vm_enter_scope({'n': ids.len}) %}
    %{ print(n) %}

    tempvar frame = LoopFrame(dst=dst, src=src);

    loop:
    let frame = [cast(ap - LoopFrame.SIZE, LoopFrame*)];
    assert [frame.dst] = [frame.src];

    let continue_copying = [ap];
    // Reserve space for continue_copying.
    let next_frame = cast(ap + 1, LoopFrame*);
    next_frame.dst = frame.dst + 1, ap++;
    next_frame.src = frame.src + 1, ap++;
    %{
        n -= 1
        ids.continue_copying = 1 if n > 0 else 0
    %}
    static_assert next_frame + LoopFrame.SIZE == ap + 1;
    jmp loop if continue_copying != 0, ap++;
    // Assert that the loop executed len times.
    len = cast(next_frame.src, felt) - cast(src, felt);

    %{ vm_exit_scope() %}
    return ();
}

func main() {
    alloc_locals;

    let (dest: felt*) = alloc();
    let source: felt* = alloc();

    assert source[0] = 1;
    assert source[1] = 1;
    assert source[2] = 1;

    memcpy(dest, source, 3);

    assert_not_zero(dest[0]);
    assert dest[0] = source[0];
    assert_not_zero(dest[1]);
    assert dest[1] = source[1];
    assert_not_zero(dest[2]);
    assert dest[2] = source[2];

    return ();
}

I added a new hint %{ print(n) %} to print the value of n in the scope. Then, in main, i call memcpy(dest, source, 3); to test here with len = 3 .

When i run this main function, i get 3 as output
Then, in the test file you created, i used 3 as an expected value for n when defining len as 3.

I also tested for fun with many other values, small or big, everything works well without surprise.
I guess testing this hint with the python cairo vm was not necessary but now we're 100% sure :)

[TAdev0]

@rodrigo-pino @cicr99 @MaksymMalicki @har777 ready for a 2nd approval !

[cicr99]

It looks great in general but there is the problem I pointed out in the comment. I see you wrote on top of the VMEnterScope hint, they are very similar but they are different ones, so you'll need to add memcpyEnterScope as a separate one.
See here an example where VMEnterScope is being used https://github.com/starkware-libs/cairo-lang/blob/efa9648f57568aad8f8a13fbf027d2de7c63c2c0/src/starkware/cairo/common/squash_dict.cairo#L28

[Alvarodb]

It looks great in general but there is the problem I pointed out in the comment. I see you wrote on top of the VMEnterScope hint, they are very similar but they are different ones, so you'll need to add memcpyEnterScope as a separate one. See here an example where VMEnterScope is being used https://github.com/starkware-libs/cairo-lang/blob/efa9648f57568aad8f8a13fbf027d2de7c63c2c0/src/starkware/cairo/common/squash_dict.cairo#L28

I've added memcpyEnterScope as a separate function, keeping the original implementation of VMEnterScope intact so this should be ok now. Thanks for the feedback!

[TAdev0]

LGTM @cicr99

[har777]

lgtm!

2 approvals already, ready to merge