Hey guys! Does anybody have an idea what is `get_caller_address` returning on an L1 handler call?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Newton

Does anybody have an idea what is `get_caller_address` returning on an L1 handler call?

Hey, I'm curious if uint256 variables are safe to use? They are using 2x128 bits, while a native felt uses only 252 bits. 

Can anyone explain?

Is uint256 math operators like uint256_le safe? Why do I need to use uint256_check?

Hi, I'm using pytest for testing cairo contract. I found that a simple starknet setup and initial call for contract cost 34 seconds. Is there a way to accelerate test?

upd: yes, [this works](https://www.notion.so/Hi-I-m-using-pytest-for-testing-cairo-contract-I-found-that-a-simple-starknet-setup-and-initial-ca-db2282fc02f2463aadaf63eac655df6f). but I found that compiling contract cost 7s and deploying contract cost 25s. These two operations are the most time-consuming

 Is there a way to accelerate pytest for cairo contract?

Hello! This is day 13 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Pedersen Hash”.  Perhaps you can help me?

```
// The following code implements a Pedersen hash chain.
// Given the [Pedersen hash](https://docs.starkware.co/starkex-docs/crypto/pedersen-hash-function) function `H`, which
// takes two field elements and returns one representing their hash,
// a hash chain on inputs x_0, x_1, ..., x_n is the result of
// H(H(...H(H(x_0, x_1), x_2), ...,x_{n-1}), x_n)
// For example, the hash chain of (1, 2, 3, 4) is H(H(H(1, 2), 3), 4).
//
// Fix the function `hash_chain` to correctly implement the
// hash chain. Run your code to test it.
//
// Note: Don't use starkware.cairo.common.hash_chain (it computes the chain differently).

// Use the Pedersen builtin.
%builtins pedersen

from starkware.cairo.common.alloc import alloc
from starkware.cairo.common.cairo_builtins import HashBuiltin
from starkware.cairo.common.hash import hash2

// Computes the Pedersen hash chain on an array of size `length` starting from `data_ptr`.
func hash_chain{hash_ptr: HashBuiltin*}(data_ptr: felt*, length: felt) -> (result: felt) {
    if (length == 2) {
        let (result) = hash2(x=[data_ptr], y=[data_ptr + 1]);
        return (result=result);
    } else {
        // Fix here:
        return (result=123456);
    }
}

func main{pedersen_ptr: HashBuiltin*}() {
    alloc_locals;
    // Allocate a new array.
    let (local data_ptr: felt*) = alloc();
    // Fill the new array with field elements.
    assert [data_ptr] = 314;
    assert [data_ptr + 1] = 159;
    // Run the hash chain.
    let (result) = hash_chain{hash_ptr=pedersen_ptr}(data_ptr=data_ptr, length=2);
    // Check the result.
    assert result = 307958720726328212653290369969069617958360335228383070119367204176047090109;

    // Fill two more cells in the array.
    assert [data_ptr + 2] = 265;
    assert [data_ptr + 3] = 358;
    // Compute the hash chain on all four cells.
    let (result) = hash_chain{hash_ptr=pedersen_ptr}(data_ptr=data_ptr, length=4);
    assert result = 1828757374677754028678056220799392919487521050857166686061558043629802016816;
    return ();
}
```

---

> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to use Pedersen Hash in StarkNet / Cairo Language?

Hello, I am facing an issue with `starknet-devnet (v0.3.1)` . I do not manage to run RPC `starknet_addInvokeTransaction` with positional parameters; yet it works with pathfinder and other vers like `starknet_estimateFee`. It returns `int() can't convert non-string with explicit base`. It is working fine on GOERLI. I have document the case on the repo https://github.com/Shard-Labs/starknet-devnet/issues/282. Does anyone have an example of a positional request to `starknet_addInvokeTransaction` on devnet that is working? The test inside the testsuite is also using named parameters. Thank you for your help

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Does anyone have an example of a positional request to `starknet_addInvokeTransaction` on devnet that is working?

There are many people who are pretty new to Cairo Language, so this thread is about some good resources, to begin with. What projects, educational courses, Github Repos etc. about StarkNet can you recommend?

---
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Every verified valid question gets $10 USDC (mainnet)

What resources (Github repos, projects) do you follow about Cairo Language? Why?

I am trying to store a negative number, and then on a function call, read it. But I only get the positive `felt` number.


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/1091)_

Cairo: How would I store negative numbers then retrieve them as negatives?

Would really like to understand how a full node for Starknet like pathfinder works

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Does anybody have an idea what is `get_caller_address` returning on an L1 handler call?

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