thrust

◆ exclusive_scan() [3/6]

template<typename DerivedPolicy , typename InputIterator , typename OutputIterator , typename T >
__host__ __device__ OutputIterator thrust::exclusive_scan ( const thrust::detail::execution_policy_base< DerivedPolicy > &  exec,
InputIterator  first,
InputIterator  last,
OutputIterator  result,
init 
)

exclusive_scan computes an exclusive prefix sum operation. The term 'exclusive' means that each result does not include the corresponding input operand in the partial sum. More precisely, init is assigned to *result and the sum of init and *first is assigned to *(result + 1), and so on. This version of exclusive_scan assumes plus as the associative operator but requires an initial value init. When the input and output sequences are the same, the scan is performed in-place.

The algorithm's execution is parallelized as determined by exec.

Parameters
execThe execution policy to use for parallelization.
firstThe beginning of the input sequence.
lastThe end of the input sequence.
resultThe beginning of the output sequence.
initThe initial value.
Returns
The end of the output sequence.
Template Parameters
DerivedPolicyThe name of the derived execution policy.
InputIteratoris a model of Input Iterator and InputIterator's value_type is convertible to OutputIterator's value_type.
OutputIteratoris a model of Output Iterator, and if x and y are objects of OutputIterator's value_type, then x + y is defined.
Tis convertible to OutputIterator's value_type.
Precondition
first may equal result but the range [first, last) and the range [result, result + (last - first)) shall not overlap otherwise.

The following code snippet demonstrates how to use exclusive_scan to compute an in-place prefix sum using the thrust::host execution policy for parallelization:

#include <thrust/scan.h>
int data[6] = {1, 0, 2, 2, 1, 3};
thrust::exclusive_scan(thrust::host, data, data + 6, data, 4); // in-place scan
// data is now {4, 5, 5, 7, 9, 10}
See also
http://www.sgi.com/tech/stl/partial_sum.html