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//! Applies the nonlinear Rectified Linear Unit.
//!
//! Non-linearity activation function: y = max(0, x)
//!
//! This is generally the preferred choice over Sigmod or TanH.
//! The max function used in ReLU is usually faster to compute than the exponentiation
//! needed in a Sigmoid layer.

use crate::co::{IBackend, SharedTensor};
use crate::conn::Relu;
use crate::conn::ReluPointwise;
use crate::layer::*;
use crate::util::ArcLock;

#[derive(Debug, Clone)]
#[allow(missing_copy_implementations)]
/// ReLU Activation Layer
pub struct ReLU;

//
// ReLU + ReLUPointwise
//
impl<B: IBackend + Relu<f32> + ReluPointwise<f32>> ILayer<B> for ReLU {
    impl_ilayer_activation!();

    fn compute_in_place(&self) -> bool {
        true
    }

    fn reshape(
        &mut self,
        backend: ::std::rc::Rc<B>,
        input_data: &mut Vec<ArcLock<SharedTensor<f32>>>,
        input_gradient: &mut Vec<ArcLock<SharedTensor<f32>>>,
        weights_data: &mut Vec<ArcLock<SharedTensor<f32>>>,
        weights_gradient: &mut Vec<ArcLock<SharedTensor<f32>>>,
        output_data: &mut Vec<ArcLock<SharedTensor<f32>>>,
        output_gradient: &mut Vec<ArcLock<SharedTensor<f32>>>,
    ) {
        if let Some(inp) = input_data.get(0) {
            let read_inp = inp.read().unwrap();
            let input_desc = read_inp.desc();
            input_gradient[0].write().unwrap().resize(input_desc).unwrap();
            output_data[0].write().unwrap().resize(input_desc).unwrap();
            output_gradient[0].write().unwrap().resize(input_desc).unwrap();
        }
    }
}

impl<B: IBackend + Relu<f32> + ReluPointwise<f32>> ComputeOutput<f32, B> for ReLU {
    fn compute_output(
        &self,
        backend: &B,
        _weights: &[&SharedTensor<f32>],
        input_data: &[&SharedTensor<f32>],
        output_data: &mut [&mut SharedTensor<f32>],
    ) {
        match input_data.get(0) {
            Some(input) => backend.relu(input, output_data[0]).unwrap(),
            None => backend.relu_pointwise(output_data[0]).unwrap(),
        }
    }
}

impl<B: IBackend + Relu<f32> + ReluPointwise<f32>> ComputeInputGradient<f32, B> for ReLU {
    fn compute_input_gradient(
        &self,
        backend: &B,
        weights_data: &[&SharedTensor<f32>],
        output_data: &[&SharedTensor<f32>],
        output_gradients: &[&SharedTensor<f32>],
        input_data: &[&SharedTensor<f32>],
        input_gradients: &mut [&mut SharedTensor<f32>],
    ) {
        match output_data.get(0) {
            Some(_) => backend
                .relu_grad(output_data[0], output_gradients[0], input_data[0], input_gradients[0])
                .unwrap(),
            None => backend.relu_pointwise_grad(input_data[0], input_gradients[0]).unwrap(),
        }
    }
}

impl<B: IBackend + Relu<f32> + ReluPointwise<f32>> ComputeParametersGradient<f32, B> for ReLU {}