Partial Sort

Configuring the kernel

template<class NthElementConfig, class MergeSortConfig = default_config>
struct partial_sort_config

Configuration of device-level partial sort.

Template Parameters:

• NthElementConfig – - configuration of device-level nth element operation. Must be nth_element_config or default_config.

• MergeSortConfig – - configuration of device-level merge sort operation. Must be merge_sort_config or default_config.

partial_sort

template<class Config = default_config, class KeysIterator, class BinaryFunction = ::rocprim::less<typename std::iterator_traits<KeysIterator>::value_type>>
hipError_t rocprim::partial_sort(void *temporary_storage, size_t &storage_size, KeysIterator keys, size_t middle, size_t size, BinaryFunction compare_function = BinaryFunction(), hipStream_t stream = 0, bool debug_synchronous = false)

Rearranges elements such that the range [0, middle) contains the sorted middle smallest elements in the range [0, size).

Overview

• The contents of the inputs are not altered by the function.

• Returns the required size of temporary_storage in storage_size if temporary_storage is a null pointer.

• Accepts custom compare_functions for partial_sort across the device.

• Streams in graph capture mode are not supported

Example

In this example a device-level partial_sort is performed where input keys are represented by an array of unsigned integers.

#include <rocprim/rocprim.hpp>

// Prepare input and output (declare pointers, allocate device memory etc.)
size_t input_size;          // e.g., 8
size_t middle;              // e.g., 4
unsigned int * keys;  // e.g., [ 6, 3, 5, 4, 1, 8, 2, 7 ]

size_t temporary_storage_size_bytes;
void * temporary_storage_ptr = nullptr;
// Get required size of the temporary storage
rocprim::partial_sort(
    temporary_storage_ptr, temporary_storage_size_bytes,
    keys, middle, input_size
);

// allocate temporary storage
hipMalloc(&temporary_storage_ptr, temporary_storage_size_bytes);

// perform partial_sort
rocprim::partial_sort(
    temporary_storage_ptr, temporary_storage_size_bytes,
    keys, middle, input_size
);
// possible keys:   [ 1, 2, 3, 4, 5, 8, 7, 6 ]

Template Parameters:

• Config – [optional] configuration of the primitive. It has to be partial_sort_config.

• KeysIterator – [inferred] random-access iterator type of the input range. Must meet the requirements of a C++ InputIterator concept. It can be a simple pointer type.

• CompareFunction – [inferred] Type of binary function that accepts two arguments of the type KeysIterator and returns a value convertible to bool. Default type is rocprim::less<>.

Parameters:

• temporary_storage – [in] pointer to a device-accessible temporary storage. When a null pointer is passed, the required allocation size (in bytes) is written to storage_size and function returns without performing the partial_sort rearrangement.

• storage_size – [inout] reference to a size (in bytes) of temporary_storage.

• keys – [inout] iterator to the input range.

• middle – [in] The index of the point till where it is sorted in the input range.

• size – [in] number of element in the input range.

• compare_function – [in] binary operation function object that will be used for comparison. The signature of the function should be equivalent to the following: bool f(const T &a, const T &b);. The signature does not need to have const &, but function object must not modify the objects passed to it. The comparator must meet the C++ named requirement Compare. The default value is BinaryFunction().

• stream – [in] [optional] HIP stream object. Default is 0 (default stream).

• debug_synchronous – [in] [optional] If true, synchronization after every kernel launch is forced in order to check for errors. Default value is false.

Returns:

hipSuccess (0) after successful rearrangement; otherwise a HIP runtime error of type hipError_t.

template<class Config = default_config, class KeysInputIterator, class KeysOutputIterator, class BinaryFunction = ::rocprim::less<typename std::iterator_traits<KeysInputIterator>::value_type>>
hipError_t rocprim::partial_sort_copy(void *temporary_storage, size_t &storage_size, KeysInputIterator keys_input, KeysOutputIterator keys_output, size_t middle, size_t size, BinaryFunction compare_function = BinaryFunction(), hipStream_t stream = 0, bool debug_synchronous = false)

Rearranges elements such that the range [0, middle) contains the sorted middle smallest elements in the range [0, size).

Overview

• The contents of the inputs are not altered by the function.

• Returns the required size of temporary_storage in storage_size if temporary_storage is a null pointer.

• Accepts custom compare_functions for partial_sort_copy across the device.

• Streams in graph capture mode are not supported

Example

In this example a device-level partial_sort_copy is performed where input keys are represented by an array of unsigned integers.

#include <rocprim/rocprim.hpp>

// Prepare input and output (declare pointers, allocate device memory etc.)
size_t input_size;          // e.g., 8
size_t middle;              // e.g., 4
unsigned int * keys_input;  // e.g., [ 6, 3, 5, 4, 1, 8, 2, 7 ]
unsigned int * keys_output; // e.g., [ 9, 9, 9, 9, 9, 9, 9, 9 ]

size_t temporary_storage_size_bytes;
void * temporary_storage_ptr = nullptr;
// Get required size of the temporary storage
rocprim::partial_sort_copy(
    temporary_storage_ptr, temporary_storage_size_bytes,
    keys_input, keys_output, middle, input_size
);

// allocate temporary storage
hipMalloc(&temporary_storage_ptr, temporary_storage_size_bytes);

// perform partial_sort
rocprim::partial_sort_copy(
    temporary_storage_ptr, temporary_storage_size_bytes,
    keys_input, keys_output, middle, input_size
);
// possible keys_output:   [ 1, 2, 3, 4, 5, 9, 9, 9 ]

Template Parameters:

• Config – [optional] configuration of the primitive. It has to be partial_sort_config.

• KeysInputIterator – [inferred] random-access iterator type of the input range. Must meet the requirements of a C++ InputIterator concept. It can be a simple pointer type.

• KeysOutputIterator – [inferred] random-access iterator type of the output range. Must meet the requirements of a C++ InputIterator concept. It can be a simple pointer type.

• CompareFunction – [inferred] Type of binary function that accepts two arguments of the type KeysIterator and returns a value convertible to bool. Default type is rocprim::less<>.

Parameters:

• temporary_storage – [in] pointer to a device-accessible temporary storage. When a null pointer is passed, the required allocation size (in bytes) is written to storage_size and function returns without performing the partial_sort_copy rearrangement.

• storage_size – [inout] reference to a size (in bytes) of temporary_storage.

• keys_input – [in] iterator to the input range.

• keys_output – [out] iterator to the output range. No overlap at all is allowed between keys_input and keys_output. keys_output should be able to be write to at least middle + 1 elements.

• middle – [in] The index of the point till where it is sorted in the input range.

• size – [in] number of element in the input range.

• compare_function – [in] binary operation function object that will be used for comparison. The signature of the function should be equivalent to the following: bool f(const T &a, const T &b);. The signature does not need to have const &, but function object must not modify the objects passed to it. The comparator must meet the C++ named requirement Compare. The default value is BinaryFunction().

• stream – [in] [optional] HIP stream object. Default is 0 (default stream).

• debug_synchronous – [in] [optional] If true, synchronization after every kernel launch is forced in order to check for errors. Default value is false.

Returns:

hipSuccess (0) after successful rearrangement; otherwise a HIP runtime error of type hipError_t.