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# Implement new operators in Orion

The Orion Framework offers an open-source ONNX runtime implementation for Validity and ZK Machine Learning. Are you interested in contributing? We sincerely appreciate your interest. This is exactly how we'll build a robust and transparent AI ecosystem! In this tutorial, you'll learn how to contribute to the Orion repository by implementing from scratch a new operator.

Throughout this tutorial, any concept that is directly explained in the official documentation will be met with a reference guiding you to the respective source. Feel free to dive in.

Orion repo uses Scarb, a Cairo package manager. You can find all information about Scarb and Cairo installation here.

The repository is structured as follows:

.

├── LICENSE

├── README.md

├── Scarb.toml

├── book.json

├── cairo_project.toml

├── docgen

├── docs

├── nodegen

├── src

│ ├── lib.cairo

│ ├── numbers

│ ├── numbers.cairo

│ ├── operators

│ ├── operators.cairo

│ ├── tests

│ ├── tests.cairo

│ └── utils.cairo

└── target

In the

`src`

directory, you'll find four distinct folders:In this tutorial we will focus on

`operators`

directory, as we will implement a new operator from scratch.Orion operators serve as the foundational components of machine learning models compliant with ONNX ops. ONNX is an open format for representing machine learning models that allows interoperability between various deep learning frameworks. It enables models to be trained in one framework and deployed in another without the need for extensive model conversion.

Orion operators represent specific computations or operations performed by machine learning models. Each operator defines a specific functionality, such as convolution, pooling, activation functions, matrix operations, and more. These operators are defined using a set of attributes and inputs that describe their behaviour and dependencies.

Ensuring compatibility with ONNX operators facilitates integration into the ONNX ecosystem. This enables researchers and developers to pre-train models using their preferred framework, before executing verifiable inferences with Orion.

We implemented two different types of operators, each having their own trait:

**Use Resources:**

This tutorial will focus specifically on implementing a new Operator in the Orion repository, and will not cover the entirety of the contribution guidelines. If you intend to contribute to Orion, we kindly ask that you read carefully the Contribution Guidelines.

In this section, I will guide you through the process of adding new operators to the Orion repository. To illustrate this, we will build the Softmax operator from scratch.

It is a non-linear activation function that takes a vector of real numbers as input and transforms them into a probability distribution over multiple classes. It's defined as follows:

$\text{softmax}(x_i) = \frac{e^{x_i}}{\sum_{j=1}^n e^{x_j}}$

In other words, the softmax function exponentiates each element of the input vector and divides it by the sum of exponentiated values across all elements. This normalization ensures that the output values lie between 0 and 1, and their sum adds up to 1, resembling a probability distribution.

Before implementing an operator in Orion, I recommend that you:

- 1.
- 2.Understand how the ONNX backend has implemented it. It's essential to maintain the operator's interface consistent with the one in ONNX.
- 3.Consider whether the operator should be implemented in
`NNTrait`

or`TensorTrait`

.

Since Softmax is a neural network operator, it needs to be implemented in

`NNTrait`

. It accepts an input tensor of a generic type 'T' and an axis along which the softmax computation will occur. Given that the resulting values must range between 0 and 1, it should return a tensor of fixed-point numbers, retaining the same shape as the input tensor.trait NNTrait<T> {

//...

fn softmax(tensor: @Tensor<T>, axis: usize) -> Tensor<FixedType>;

}

In the

`src/operators/nn/functional`

directory, create a new file named `softmax.cairo`

.The

`functional`

folder is where all the business logic resides. All functions should be implemented with generic type.A softmax function can be implemented as follows:

`Softmax(input, axis) = Exp(input) / ReduceSum(Exp(input), axis=axis)`

Here's the implementation in

`softmax.cairo`

:use orion::operators::tensor::core::{Tensor, TensorTrait};

/// Cf: NNTrait::softmax docstring

fn softmax<

T,

impl TTensor: TensorTrait<T>,

impl TTensor: TensorTrait<T>,

impl TTensorDiv: Div<Tensor<T>>,

impl TCopy: Copy<T>,

impl TDrop: Drop<T>,

>(

z: @Tensor<T>, axis: usize

) -> Tensor<T> {

let exp_tensor = z.exp();

let sum = exp_tensor.reduce_sum(axis, true);

let softmax = exp_tensor / sum;

return softmax;

}

Now, we need to add the softmax function into the different representations. In

`nn/implementations/nn_fp8x23.cairo`

, import the business logic and add the softmax implementation.// In nn_fp8x23.cairo

impl FP8x23NN of NNTrait<FP8x23> {

// [...]

fn softmax(tensor: @Tensor<FP8x23>, axis: usize) -> Tensor<FP8x23> {

functional::softmax::softmax(tensor, axis)

}

}

Do the same for all other fixed point implementations (

`FP16x16NN`

, `FP32x32NN`

, `FP64x64NN`

). As softmax only support fixed point tensors, it should panic for other implementations. Below an example with `U32NN`

.// In nn_u32.cairo

impl U32NN of NNTrait<u32> {

// [...]

fn softmax(tensor: @Tensor<u32>, axis: usize) -> Tensor<u32> {

panic(array!['not supported!'])

}

}

Navigate back to

`operators/nn/core.cairo`

and prior to the declaration of the softmax function, write the docstring and list it preceding the trait as shown below. This step is useful for generating the documentation during the preparation of your Pull Request, which can be achieved with `scarb run docgen`

command. We use a docstring style similar to Rust's docstring, with a few variations./// Trait

///

/// [...]

/// softmax - Computes softmax activations.

trait NNTrait<T> {

/// [...]

/// # NNTrait::softmax

///

/// ```rust

/// fn softmax(tensor: @Tensor<T>, axis: usize) -> Tensor<T>;

/// ```

///

/// Applies the Softmax function to an n-dimensional input Tensor rescaling them so that the elements of the n-dimensional output Tensor lie in the range \[0,1] and sum to 1.

///

/// $$

/// \text{softmax}(x_i) = \frac{e^{x_i}}{\sum_{j=1}^n e^{x_j}}

/// $$

///

/// ## Args

///

/// * `tensor`(`@Tensor<T>`) - The input tensor.

/// * `axis`(`usize`) - The axis along which to compute the softmax.

///

/// ## Returns

///

/// A Tensor of fixed point numbers with the same shape than the input Tensor.

///

/// ## Type Constraints

///

/// Constrain input and output types to fixed point tensors.

///

/// ## Examples

///

/// ```rust

/// use array::{ArrayTrait, SpanTrait};

///

/// use orion::operators::tensor::{TensorTrait, Tensor, FP8x23};

/// use orion::operators::nn::{NNTrait, FP8x23NN};

/// use orion::numbers::{FP8x23, FixedTrait};

///

/// fn softmax_example() -> Tensor<FP8x23> {

/// let tensor = TensorTrait::<FP8x23>::new(

/// shape: array![2, 2].span(),

/// data: array![

/// NNTrait::new(0, false),

/// NNTrait::new(1, false),

/// NNTrait::new(2, false),

/// NNTrait::new(3, false),

/// ]

/// .span(),

/// );

///

/// return NNTrait::softmax(@tensor, 1);

/// }

/// >>> [[2255697,6132911],[2255697,6132911]]

/// // The fixed point representation of

/// // [[0.2689, 0.7311],[0.2689, 0.7311]]

/// ```

///

fn softmax(tensor: @Tensor<T>, axis: usize) -> Tensor<T>;

}

Voilà! We have successfully implemented the softmax function in

`NNTrait`

!Now, let's proceed to testing the softmax operator we've just implemented. When testing an operator in Orion, you should ensure to test across all types of implementation.

To simplify the task of writing tests, and get closer to ONNX tests, we've designed

**Nodegen**! It lets you write your test in Python/Numpy, then generate the following Cairo code:- Input data
- Expected output data
- Your tests

First, we'll create a

`softmax.py`

file in the `nodegen/node`

directory. Next, we'll define a softmax function in python. You can find the python function in ONNX implementation directory.import numpy as np

def softmax(x: np.ndarray, axis: int = -1) -> np.ndarray:

x_max = np.max(x, axis=axis, keepdims=True)

tmp = np.exp(x - x_max)

s = np.sum(tmp, axis=axis, keepdims=True)

return tmp / s

Finally, we create a Softmax class, containing tests for each dtypes.

import numpy as np

from nodegen.node import RunAll

from ..helpers import make_test, to_fp, Tensor, Dtype, FixedImpl, Trait

def softmax(x: np.ndarray, axis: int = -1) -> np.ndarray:

x_max = np.max(x, axis=axis, keepdims=True)

tmp = np.exp(x - x_max)

s = np.sum(tmp, axis=axis, keepdims=True)

return tmp / s

class Softmax(RunAll):

@staticmethod

# We test here with fp8x23 implementation.

def fp8x23():

# Create a random numpy array:

x = np.random.randint(-3, 3, (2, 2)).astype(np.float64)

# Ddefine the expected result:

y = softmax(x, 0)

# Convert the input and output to Tensor class, similar to Orion's Tensor struct:

x = Tensor(Dtype.FP8x23, x.shape, to_fp(x.flatten(), FixedImpl.FP8x23))

# Convert the floats values in `y` to fixed points with `to_fp` method:

y = Tensor(Dtype.FP8x23, y.shape, to_fp(y.flatten(), FixedImpl.FP8x23))

# Define the name of the generated folder.

name = "softmax_fp8x23"

# Invoke `make_test` method to generate corresponding Cairo tests:

make_test(

[x], # List of input tensors.

y, # The expected output result.

"NNTrait::softmax(@input_0, 0)", # The code signature.

name, # The name of the generated folder.

Trait.NN # The trait, if the function is present in either the TensorTrait or NNTrait.

)

# We test here with fp16x16 implementation.

@staticmethod

def fp16x16():

x = np.random.uniform(-3, 3, (2, 2)).astype(np.float64)

y = softmax(x, 1)

x = Tensor(Dtype.FP16x16, x.shape, to_fp(

x.flatten(), FixedImpl.FP16x16))

y = Tensor(Dtype.FP16x16, y.shape, to_fp(

y.flatten(), FixedImpl.FP16x16))

name = "softmax_fp16x16"

make_test([x], y, "NNTrait::softmax(@input_0, 1)",

name, Trait.NN)

Once set up, you can generate tests and data by executing

`scarb run nodegen softmax`

.The above code will generate 6 test files located in

`tests/src/nodes`

. As an example, here's the content of the `softmax_fp8x23.cairo`

generated file:// softmax_fp8x23.cairo

mod input_0;

mod output_0;

use orion::operators::nn::NNTrait;

use orion::numbers::FixedTrait;

use orion::operators::nn::FP8x23NN;

use orion::operators::tensor::FP8x23TensorPartialEq;

use orion::utils::assert_eq;

#[test]

#[available_gas(2000000000)]

fn test_softmax_fp8x23() {

let input_0 = input_0::input_0();

let z = output_0::output_0();

let y = NNTrait::softmax(@input_0, 0);

assert_eq(y, z);

}

If you'd like to expand the tests with additional cases, feel free to edit the generated Cairo file.

You're now ready to prepare your Pull Request. Please ensure you thoroughly read the Contribution Guidelines before making your first PR. Your contribution is greatly appreciated, and we sincerely value your interest .

Orion leverages Cairo to guarantee the reliability of inference, providing developers with a user-friendly framework to build complex and verifiable machine learning models. We invite the community to join us in shaping a future where trustworthy AI becomes a reliable resource for all.

Last modified 20d ago