mesytec-mnode/external/taskflow-3.8.0/doxygen/cudaflow_algorithms/cudaflow_scan.dox

namespace tf {

/** @page cudaFlowScan Parallel Scan

%cudaFlow provides template methods to create parallel scan tasks 
on a CUDA GPU.

@tableofcontents

@section CUDAParallelScanIncludeTheHeader Include the Header

You need to include the header file, `%taskflow/cuda/algorithm/scan.hpp`, 
for creating a parallel-scan task.

@section cudaFlowScanARangeOfItems Scan a Range of Items

tf::cudaFlow::inclusive_scan computes an inclusive prefix sum operation using
the given binary operator over a range of elements specified by <tt>[first, last)</tt>.
The term &quot;inclusive&quot; means that the i-th input element is included 
in the i-th sum.
The following code computes the inclusive prefix sum over an input array and
stores the result in an output array.

@code{.cpp}
const size_t N = 1000000;
int* input  = tf::cuda_malloc_shared<int>(N);  // input  vector
int* output = tf::cuda_malloc_shared<int>(N);  // output vector

// initializes the data
for(size_t i=0; i<N; input[i++]=rand());
 
// creates a cudaFlow of one task to perform inclusive scan 
tf::cudaFlow cf;
tf::cudaTask task = cf.inclusive_scan(
  input, input + N, output, [] __device__ (int a, int b) { return a + b; }
);
cf.offload();

// verifies the result
for(size_t i=1; i<N; i++) {
  assert(output[i] == output[i-1] + input[i]);
}
@endcode

On the other hand, tf::cudaFlow::exclusive_scan computes an exclusive prefix sum operation.
The term &quot;exclusive&quot; means that the i-th input element is @em NOT included 
in the i-th sum.

@code{.cpp}
// creates a cudaFlow of one task to perform exclusive scan 
tf::cudaFlow cf;
tf::cudaTask task = cf.exclusive_scan(
  input, input + N, output, [] __device__ (int a, int b) { return a + b; }
);
cf.offload();

// verifies the result
for(size_t i=1; i<N; i++) {
  assert(output[i] == output[i-1] + input[i-1]);
}
@endcode

@section cudaFlowScanTransformedItems Scan a Range of Transformed Items

tf::cudaFlow::transform_inclusive_scan transforms 
each item in the range <tt>[first, last)</tt>
and computes an inclusive prefix sum over these transformed items.
The following code multiplies each item by 10 and then compute the inclusive prefix sum
over 1000000 transformed items.

@code{.cpp}
const size_t N = 1000000;
int* input  = tf::cuda_malloc_shared<int>(N);  // input  vector
int* output = tf::cuda_malloc_shared<int>(N);  // output vector

// initializes the data
for(size_t i=0; i<N; i++) 
  input[i] = rand();
} 

// creates a cudaFlow of one task to inclusively scan over transformed input 
tf::cudaFlow cf;
tf::cudaTask task = cf.transform_inclusive_scan(
  input, input + N, output, 
  [] __device__ (int a, int b) { return a + b; },  // binary scan operator
  [] __device__ (int a) { return a*10; }           // unary transform operator
);
cf.offload();

// verifies the result
for(size_t i=1; i<N; i++) {
  assert(output[i] == output[i-1] + input[i] * 10);
}
@endcode

Similarly, tf::cudaFlow::transform_exclusive_scan performs an exclusive prefix sum
over a range of transformed items.
The following code computes the exclusive prefix sum over 1000000 transformed items
each multiplied by 10.

@code{.cpp}
const size_t N = 1000000;
int* input  = tf::cuda_malloc_shared<int>(N);  // input  vector
int* output = tf::cuda_malloc_shared<int>(N);  // output vector

// initializes the data
for(size_t i=0; i<N; input[i++]=rand()); 

// creates a cudaFlow of one task to exclusively scan over transformed input 
tf::cudaFlow cf;
tf::cudaTask task = cf.transform_exclusive_scan(
  input, input + N, output, 
  [] __device__ (int a, int b) { return a + b; },  // binary scan operator
  [] __device__ (int a) { return a*10; }           // unary transform operator
);
cf.offload();

// verifies the result
for(size_t i=1; i<N; i++) {
  assert(output[i] == output[i-1] + input[i-1] * 10);
}
@endcode

@section cudaFlowScanMiscellaneousItems Miscellaneous Items

Parallel scan algorithms are also available in tf::cudaFlowCapturer
with the same API.

*/
}