template<typename DerivedPolicy , typename InputIterator , typename OutputIterator , typename T , typename AssociativeOperator >
__host__ __device__ OutputIterator thrust::exclusive_scan |
( |
const thrust::detail::execution_policy_base< DerivedPolicy > & |
exec, |
|
|
InputIterator |
first, |
|
|
InputIterator |
last, |
|
|
OutputIterator |
result, |
|
|
T |
init, |
|
|
AssociativeOperator |
binary_op |
|
) |
| |
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 value binary_op(init, *first)
is assigned to *(result + 1)
, and so on. This version of the function requires both an associative operator and an initial value init
. 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
.
- 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. |
init | The initial value. |
binary_op | The associatve operator used to 'sum' values. |
- Returns
- The end 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 OutputIterator's value_type is convertible to both AssociativeOperator's first_argument_type and second_argument_type . |
T | is convertible to OutputIterator's value_type . |
AssociativeOperator | is a model of Binary Function and AssociativeOperator's result_type is 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[10] = {-5, 0, 2, -3, 2, 4, 0, -1, 2, 8};
- See also
- https://en.cppreference.com/w/cpp/algorithm/partial_sum