thrust::exclusive_scan

Defined in thrust/scan.h

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

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, 0 is assigned to *result and the sum of 0 and *first is assigned to *(result + 1), and so on. This version of exclusive_scan assumes plus as the associative operator and 0 as the initial value. When the input and output sequences are the same, the scan is performed in-place.

Results are not deterministic for pseudo-associative operators (e.g., addition of floating-point types). Results for pseudo-associative operators may vary from run to run.

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

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>
#include <thrust/execution_policy.h>
...

int data[6] = {1, 0, 2, 2, 1, 3};

thrust::exclusive_scan(thrust::host, data, data + 6, data); // in-place scan

// data is now {0, 1, 1, 3, 5, 6}

Parameters
  • exec – The execution policy to use for parallelization.

  • first – The beginning of the input sequence.

  • last – The end of the input sequence.

  • result – The beginning of the output sequence.

Template Parameters
  • DerivedPolicy – The name of the derived execution policy.

  • InputIterator – is a model of Input Iterator and InputIterator's value_type is convertible to OutputIterator's value_type.

  • OutputIterator – is a model of Output Iterator, and if x and y are objects of OutputIterator's value_type, then x + y is defined. If T is OutputIterator's value_type, then T(0) is defined.

Returns

The end of the output sequence.

Pre

first may equal result but the range [first, last) and the range [result, result + (last - first)) shall not overlap otherwise.