conv_2d_backward_expr.hpp

//=======================================================================
// Copyright (c) 2014-2023 Baptiste Wicht
// Distributed under the terms of the MIT License.
// (See accompanying file LICENSE or copy at
//  http://opensource.org/licenses/MIT)
//=======================================================================

#pragma once

#include "etl/expr/base_temporary_expr.hpp"

//Get the implementations
#include "etl/impl/conv.hpp"

namespace etl {

template <etl_2d A, etl_2d B, size_t S1, size_t S2, size_t P1, size_t P2, bool Flipped>
struct conv_2d_backward_expr : base_temporary_expr_bin<conv_2d_backward_expr<A, B, S1, S2, P1, P2, Flipped>, A, B> {
    using value_type  = value_t<A>;                                           
    using this_type   = conv_2d_backward_expr<A, B, S1, S2, P1, P2, Flipped>; 
    using base_type   = base_temporary_expr_bin<this_type, A, B>;             
    using left_traits = decay_traits<A>;                                      

    static constexpr auto storage_order = left_traits::storage_order; 

    static constexpr bool gpu_computable = cudnn_enabled && impl::cudnn::conv_possible_<A, B>;

    explicit conv_2d_backward_expr(A a, B b) : base_type(a, b) {
        //Nothing else to init
    }

    // Assignment functions

    template <etl_2d I, etl_2d K, etl_2d C>
    static void check([[maybe_unused]] const I& input, [[maybe_unused]] const K& kernel, [[maybe_unused]] const C& conv) {
        if constexpr (all_fast<A, B, C>) {
            static_assert(etl::dim<0, C>() == S1 * (etl::dim<0, I>() - 1) + etl::dim<0, K>() - 2 * P1, "Invalid dimensions for conv2_backward");
            static_assert(etl::dim<1, C>() == S2 * (etl::dim<1, I>() - 1) + etl::dim<1, K>() - 2 * P2, "Invalid dimensions for conv2_backward");
        } else {
            cpp_assert(etl::dim(conv, 0) == S1 * (etl::dim(input, 0) - 1) + etl::dim(kernel, 0) - 2 * P1, "Invalid dimensions for conv2_backward");
            cpp_assert(etl::dim(conv, 1) == S2 * (etl::dim(input, 1) - 1) + etl::dim(kernel, 1) - 2 * P2, "Invalid dimensions for conv2_backward");
        }
    }

    template <etl_2d C>
    void assign_to(C&& conv) const {
        inc_counter("temp:assign");

        auto& input  = this->a();
        auto& kernel = this->b();

        check(input, kernel, conv);

        // Need K1 / K2 to compute transposed padding
        const size_t K1 = etl::dim<0>(kernel);
        const size_t K2 = etl::dim<1>(kernel);

        if constexpr (Flipped) {
            // 1. Handle unit strides
            if constexpr (S1 == 1 && S2 == 1) {
                if constexpr (P1 == 0 && P2 == 0) {
                    // Unit strides, non-zero padding -> Full convolution
                    detail::conv2_full_flipped_impl::apply(input, kernel, conv);
                } else {
                    // Unit strides, zero padding -> Valid convolution with the correct padding
                    detail::dyn_conv2_valid_flipped_impl::apply(input, kernel, conv, 1, 1, K1 - P1 - 1, K2 - P2 - 1);
                }
            }
            // 2. Handle non_unit strides
            else {
                // Fractionally-strided convolution needs inner padding of the input
                auto strided_input = impl::common::inner_pad(input, S1, S2);

                if constexpr (P1 == 0 && P2 == 0) {
                    // Non-unit strides, non-zero padding -> Fractionally-strided full convolution
                    detail::conv2_full_flipped_impl::apply(strided_input, kernel, conv);
                } else {
                    // Non-unit strides, zero padding -> Fractionally-strided Valid convolution with the correct padding
                    detail::dyn_conv2_valid_flipped_impl::apply(strided_input, kernel, conv, 1, 1, K1 - P1 - 1, K2 - P2 - 1);
                }
            }
        } else {
            // 1. Handle unit strides
            if constexpr (S1 == 1 && S2 == 1) {
                if constexpr (P1 == 0 && P2 == 0) {
                    // Unit strides, non-zero padding -> Full convolution
                    detail::conv2_full_impl::apply(input, kernel, conv);
                } else {
                    // Unit strides, zero padding -> Valid convolution with the correct padding
                    detail::dyn_conv2_valid_impl::apply(input, kernel, conv, 1, 1, K1 - P1 - 1, K2 - P2 - 1);
                }
            }
            // 2. Handle non_unit strides
            else {
                // Fractionally-strided convolution needs inner padding of the input
                auto strided_input = impl::common::inner_pad(input, S1, S2);

                if constexpr (P1 == 0 && P2 == 0) {
                    // Non-unit strides, non-zero padding -> Fractionally-strided full convolution
                    detail::conv2_full_impl::apply(strided_input, kernel, conv);
                } else {
                    // Non-unit strides, zero padding -> Fractionally-strided Valid convolution with the correct padding
                    detail::dyn_conv2_valid_impl::apply(strided_input, kernel, conv, 1, 1, K1 - P1 - 1, K2 - P2 - 1);
                }
            }
        }
    }

    template <etl_2d L>
    void assign_add_to(L&& lhs) const {
        std_add_evaluate(*this, lhs);
    }

    template <etl_2d L>
    void assign_sub_to(L&& lhs) const {
        std_sub_evaluate(*this, lhs);
    }

    template <etl_2d L>
    void assign_mul_to(L&& lhs) const {
        std_mul_evaluate(*this, lhs);
    }

    template <etl_2d L>
    void assign_div_to(L&& lhs) const {
        std_div_evaluate(*this, lhs);
    }

    template <etl_2d L>
    void assign_mod_to(L&& lhs) const {
        std_mod_evaluate(*this, lhs);
    }

    friend std::ostream& operator<<(std::ostream& os, const conv_2d_backward_expr& expr) {
        return os << "conv2_backward(" << expr._a << ", " << expr._b << ")";
    }
};

template <etl_2d A, etl_2d B, size_t S1, size_t S2, size_t P1, size_t P2, bool Flipped>
struct etl_traits<etl::conv_2d_backward_expr<A, B, S1, S2, P1, P2, Flipped>> {
    using expr_t       = etl::conv_2d_backward_expr<A, B, S1, S2, P1, P2, Flipped>; 
    using left_expr_t  = std::decay_t<A>;                                           
    using right_expr_t = std::decay_t<B>;                                           
    using left_traits  = etl_traits<left_expr_t>;                                   
    using right_traits = etl_traits<right_expr_t>;                                  
    using value_type   = value_t<A>;                                                

    static constexpr bool is_etl         = true;                                 
    static constexpr bool is_transformer = false;                                
    static constexpr bool is_view        = false;                                
    static constexpr bool is_magic_view  = false;                                
    static constexpr bool is_fast        = all_fast<A, B>;                       
    static constexpr bool is_linear      = false;                                
    static constexpr bool is_thread_safe = true;                                 
    static constexpr bool is_value       = false;                                
    static constexpr bool is_direct      = true;                                 
    static constexpr bool is_generator   = false;                                
    static constexpr bool is_padded      = false;                                
    static constexpr bool is_aligned     = true;                                 
    static constexpr bool is_temporary   = true;                                 
    static constexpr bool gpu_computable = is_gpu_t<value_type> && cuda_enabled; 
    static constexpr order storage_order = left_traits::storage_order;           

    template <vector_mode_t V>
    static constexpr bool vectorizable = true;

    template <size_t DD>
    static constexpr size_t dim() {
        return DD == 0 ? (S1 * (etl::dim<0, A>() - 1) + etl::dim<0, B>() - 2 * P1) : (S2 * (etl::dim<1, A>() - 1) + etl::dim<1, B>() - 2 * P2);
    }

    static size_t dim(const expr_t& e, size_t d) {
        if (d == 0) {
            return S1 * (etl::dim(e._a, 0) - 1) + etl::dim(e._b, 0) - 2 * P1;
        } else {
            return S2 * (etl::dim(e._a, 1) - 1) + etl::dim(e._b, 1) - 2 * P2;
        }
    }

    static size_t size(const expr_t& e) {
        return (S1 * (etl::dim(e._a, 0) - 1) + etl::dim(e._b, 0) - 2 * P1) * (S2 * (etl::dim(e._a, 1) - 1) + etl::dim(e._b, 1) - 2 * P2);
    }

    static constexpr size_t size() {
        return (S1 * (etl::dim<0, A>() - 1) + etl::dim<0, B>() - 2 * P1) * (S2 * (etl::dim<1, A>() - 1) + etl::dim<1, B>() - 2 * P2);
    }

    static constexpr size_t dimensions() {
        return 2;
    }

    static constexpr int complexity() noexcept {
        return -1;
    }
};

template <size_t S1 = 1, size_t S2 = 1, size_t P1 = 0, size_t P2 = 0, etl_2d A, etl_2d B>
conv_2d_backward_expr<detail::build_type<A>, detail::build_type<B>, S1, S2, P1, P2, false> conv_2d_backward(A&& a, B&& b) {
    return conv_2d_backward_expr<detail::build_type<A>, detail::build_type<B>, S1, S2, P1, P2, false>{a, b};
}

template <size_t S1 = 1, size_t S2 = 1, size_t P1 = 0, size_t P2 = 0, etl_2d A, etl_2d B, etl_2d C>
auto conv_2d_backward(A&& a, B&& b, C&& c) {
    c = conv_2d_backward<S1, S2, P1, P2>(a, b);

    return c;
}

template <size_t S1 = 1, size_t S2 = 1, size_t P1 = 0, size_t P2 = 0, etl_2d A, etl_2d B>
conv_2d_backward_expr<detail::build_type<A>, detail::build_type<B>, S1, S2, P1, P2, true> conv_2d_backward_flipped(A&& a, B&& b) {
    return conv_2d_backward_expr<detail::build_type<A>, detail::build_type<B>, S1, S2, P1, P2, true>{a, b};
}

template <size_t S1 = 1, size_t S2 = 1, size_t P1 = 0, size_t P2 = 0, etl_2d A, etl_2d B, etl_2d C>
auto conv_2d_backward_flipped(A&& a, B&& b, C&& c) {
    c = conv_2d_backward_flipped<S1, S2, P1, P2>(a, b);

    return c;
}

} //end of namespace etl