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/*
* Copyright 2008-2009 NVIDIA Corporation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <thrust/extrema.h>
#include <cusp/detail/device/arch.h>
#include <cusp/detail/device/common.h>
#include <cusp/detail/device/utils.h>
#include <cusp/detail/device/texture.h>
#include <thrust/device_ptr.h>
namespace cusp
{
namespace detail
{
namespace device
{
////////////////////////////////////////////////////////////////////////
// DIA SpMV kernels
///////////////////////////////////////////////////////////////////////
//
// Diagonal matrices arise in grid-based discretizations using stencils.
// For instance, the standard 5-point discretization of the two-dimensional
// Laplacian operator has the stencil:
// [ 0 -1 0 ]
// [ -1 4 -1 ]
// [ 0 -1 0 ]
// and the resulting DIA format has 5 diagonals.
//
// spmv_dia
// Each thread computes y[i] += A[i,:] * x
// (the dot product of the i-th row of A with the x vector)
//
// spmv_dia_tex
// Same as spmv_dia, except x is accessed via texture cache.
//
template <typename IndexType, typename ValueType, unsigned int BLOCK_SIZE, bool UseCache>
__launch_bounds__(BLOCK_SIZE,1)
__global__ void
spmv_dia_kernel(const IndexType num_rows,
const IndexType num_cols,
const IndexType num_diagonals,
const IndexType pitch,
const IndexType * diagonal_offsets,
const ValueType * values,
const ValueType * x,
ValueType * y)
{
__shared__ IndexType offsets[BLOCK_SIZE];
const IndexType thread_id = BLOCK_SIZE * blockIdx.x + threadIdx.x;
const IndexType grid_size = BLOCK_SIZE * gridDim.x;
for(IndexType base = 0; base < num_diagonals; base += BLOCK_SIZE)
{
// read a chunk of the diagonal offsets into shared memory
const IndexType chunk_size = thrust::min(IndexType(BLOCK_SIZE), num_diagonals - base);
if(threadIdx.x < chunk_size)
offsets[threadIdx.x] = diagonal_offsets[base + threadIdx.x];
__syncthreads();
// process chunk
for(IndexType row = thread_id; row < num_rows; row += grid_size)
{
ValueType sum = (base == 0) ? ValueType(0) : y[row];
// index into values array
IndexType idx = row + pitch * base;
for(IndexType n = 0; n < chunk_size; n++)
{
const IndexType col = row + offsets[n];
if(col >= 0 && col < num_cols)
{
const ValueType A_ij = values[idx];
sum += A_ij * fetch_x<UseCache>(col, x);
}
idx += pitch;
}
y[row] = sum;
}
// wait until all threads are done reading offsets
__syncthreads();
}
}
template <bool UseCache,
typename Matrix,
typename ValueType>
void __spmv_dia(const Matrix& A,
const ValueType* x,
ValueType* y)
{
typedef typename Matrix::index_type IndexType;
const size_t BLOCK_SIZE = 256;
const size_t MAX_BLOCKS = cusp::detail::device::arch::max_active_blocks(spmv_dia_kernel<IndexType, ValueType, BLOCK_SIZE, UseCache>, BLOCK_SIZE, (size_t) sizeof(IndexType) * BLOCK_SIZE);
const size_t NUM_BLOCKS = std::min<size_t>(MAX_BLOCKS, DIVIDE_INTO(A.num_rows, BLOCK_SIZE));
const IndexType num_diagonals = A.values.num_cols;
const IndexType pitch = A.values.pitch;
// TODO can this be removed?
if (num_diagonals == 0)
{
// empty matrix
thrust::fill(thrust::device_pointer_cast(y), thrust::device_pointer_cast(y) + A.num_rows, ValueType(0));
return;
}
if (UseCache)
bind_x(x);
spmv_dia_kernel<IndexType, ValueType, BLOCK_SIZE, UseCache> <<<NUM_BLOCKS, BLOCK_SIZE>>>
(A.num_rows, A.num_cols, num_diagonals, pitch,
thrust::raw_pointer_cast(&A.diagonal_offsets[0]),
thrust::raw_pointer_cast(&A.values.values[0]),
x, y);
if (UseCache)
unbind_x(x);
}
template <typename Matrix,
typename ValueType>
void spmv_dia(const Matrix& A,
const ValueType* x,
ValueType* y)
{
__spmv_dia<false>(A, x, y);
}
template <typename Matrix,
typename ValueType>
void spmv_dia_tex(const Matrix& A,
const ValueType* x,
ValueType* y)
{
__spmv_dia<true>(A, x, y);
}
} // end namespace device
} // end namespace detail
} // end namespace cusp
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