# dlib C++ Library - cublas_dlibapi.cpp

    // Copyright (C) 2015  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_DNN_CuBLAS_CPP_
    #define DLIB_DNN_CuBLAS_CPP_

    #ifdef DLIB_USE_CUDA

    #include "cublas_dlibapi.h"
    #include "cuda_utils.h"

    #include <cublas_v2.h>
    #include <vector>

    static const char* cublas_get_error_string(cublasStatus_t s)
    {
        switch(s)
        {
            case CUBLAS_STATUS_NOT_INITIALIZED:
                return "CUDA Runtime API initialization failed.";
            case CUBLAS_STATUS_ALLOC_FAILED:
                return "CUDA Resources could not be allocated.";
            default:
                return "A call to cuBLAS failed";
        }
    }

    // Check the return value of a call to the cuBLAS runtime for an error condition.
    #define CHECK_CUBLAS(call)                                                      \
    do{                                                                              \
        const cublasStatus_t error = call;                                         \
        if (error != CUBLAS_STATUS_SUCCESS)                                        \
        {                                                                          \
            std::ostringstream sout;                                               \
            sout << "Error while calling " << #call << " in file " << __FILE__ << ":" << __LINE__ << ". ";\
            sout << "code: " << error << ", reason: " << cublas_get_error_string(error);\
            throw dlib::cublas_error(sout.str());                            \
        }                                                                          \
    }while(false)

    namespace dlib
    {
        namespace cuda
        {

        // -----------------------------------------------------------------------------------

            class cublas_context
            {
            public:
                // not copyable
                cublas_context(const cublas_context&) = delete;
                cublas_context& operator=(const cublas_context&) = delete;

                cublas_context()
                {
                    handles.resize(16);
                }
                ~cublas_context()
                {
                    for (auto h : handles)
                    {
                        if (h)
                            cublasDestroy(h);
                    }
                }

                cublasHandle_t get_handle (
                )
                {
                    int new_device_id;
                    CHECK_CUDA(cudaGetDevice(&new_device_id));
                    // make room for more devices if needed
                    if (new_device_id >= (long)handles.size())
                        handles.resize(new_device_id+16);

                    // If we don't have a handle already for this device then make one
                    if (!handles[new_device_id])
                        CHECK_CUBLAS(cublasCreate(&handles[new_device_id]));

                    // Finally, return the handle for the current device
                    return handles[new_device_id];
                }

            private:

                std::vector<cublasHandle_t> handles;
            };

            static cublasHandle_t context()
            {
                thread_local cublas_context c;
                return c.get_handle();
            }

        // -----------------------------------------------------------------------------------

            void gemm (
                float beta,
                tensor& dest,
                float alpha,
                const tensor& lhs,
                bool trans_lhs,
                const tensor& rhs,
                bool trans_rhs
            )
            {
                // Recall that BLAS uses column major order so to deal with that we flip the
                // order of the lhs and rhs arguments.
                const auto transa = trans_lhs ? CUBLAS_OP_T : CUBLAS_OP_N;
                const auto transb = trans_rhs ? CUBLAS_OP_T : CUBLAS_OP_N;

                const int dest_nr = dest.num_samples();
                const int dest_nc = dest.size()/dest_nr;
                const int lhs_nr = lhs.num_samples();
                const int lhs_nc = lhs.size()/lhs_nr;
                const int rhs_nr = rhs.num_samples();
                const int rhs_nc = rhs.size()/rhs_nr;
                if (trans_lhs && trans_rhs)
                {
                    DLIB_ASSERT( dest_nr == lhs_nc &&
                                  dest_nc == rhs_nr &&
                                  lhs_nr == rhs_nc)
                }
                else if (!trans_lhs && trans_rhs)
                {
                    DLIB_ASSERT( dest_nr == lhs_nr &&
                                  dest_nc == rhs_nr &&
                                  lhs_nc == rhs_nc)
                }
                else if (trans_lhs && !trans_rhs)
                {
                    DLIB_ASSERT( dest_nr == lhs_nc &&
                                  dest_nc == rhs_nc &&
                                  lhs_nr == rhs_nr)
                }
                else
                {
                    DLIB_ASSERT( dest_nr == lhs_nr &&
                                  dest_nc == rhs_nc &&
                                  lhs_nc == rhs_nr)
                }

                const int k = trans_rhs ? rhs_nc : rhs_nr;
                CHECK_CUBLAS(cublasSgemm(context(),
                                  transb,
                                  transa,
                                  dest_nc, dest_nr, k,
                                  &alpha,
                                  rhs.device(), rhs_nc,
                                  lhs.device(), lhs_nc,
                                  &beta,
                                  dest.device(),dest_nc));
            }

        // ------------------------------------------------------------------------------------

        }
    }

    #endif // DLIB_USE_CUDA

    #endif // DLIB_DNN_CuBLAS_CPP_