cub/thread/thread_scan.cuh

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/**
 * \file
 * Thread utilities for sequential prefix scan over statically-sized array types
 */

#pragma once

#include "../config.cuh"
#include "../thread/thread_operators.cuh"

/// Optional outer namespace(s)
CUB_NS_PREFIX

/// CUB namespace
namespace cub {

/// Internal namespace (to prevent ADL mishaps between static functions when mixing different CUB installations)
namespace internal {


/**
 * \addtogroup UtilModule
 * @{
 */

/**
 * \name Sequential prefix scan over statically-sized array types
 * @{
 */

template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanExclusive(
    T                   inclusive,
    T                   exclusive,
    T                   *input,                 ///< [in] Input array
    T                   *output,                ///< [out] Output array (may be aliased to \p input)
    ScanOp              scan_op,                ///< [in] Binary scan operator
    Int2Type<LENGTH>    /*length*/)
{
    #pragma unroll
    for (int i = 0; i < LENGTH; ++i)
    {
        inclusive = scan_op(exclusive, input[i]);
        output[i] = exclusive;
        exclusive = inclusive;
    }

    return inclusive;
}


/**
 * \brief Perform a sequential exclusive prefix scan over \p LENGTH elements of the \p input array, seeded with the specified \p prefix.  The aggregate is returned.
 *
 * \tparam LENGTH     LengthT of \p input and \p output arrays
 * \tparam T          <b>[inferred]</b> The data type to be scanned.
 * \tparam ScanOp     <b>[inferred]</b> Binary scan operator type having member <tt>T operator()(const T &a, const T &b)</tt>
 */
template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanExclusive(
    T           *input,                 ///< [in] Input array
    T           *output,                ///< [out] Output array (may be aliased to \p input)
    ScanOp      scan_op,                ///< [in] Binary scan operator
    T           prefix,                 ///< [in] Prefix to seed scan with
    bool        apply_prefix = true)    ///< [in] Whether or not the calling thread should apply its prefix.  If not, the first output element is undefined.  (Handy for preventing thread-0 from applying a prefix.)
{
    T inclusive = input[0];
    if (apply_prefix)
    {
        inclusive = scan_op(prefix, inclusive);
    }
    output[0] = prefix;
    T exclusive = inclusive;

    return ThreadScanExclusive(inclusive, exclusive, input + 1, output + 1, scan_op, Int2Type<LENGTH - 1>());
}


/**
 * \brief Perform a sequential exclusive prefix scan over the statically-sized \p input array, seeded with the specified \p prefix.  The aggregate is returned.
 *
 * \tparam LENGTH     <b>[inferred]</b> LengthT of \p input and \p output arrays
 * \tparam T          <b>[inferred]</b> The data type to be scanned.
 * \tparam ScanOp     <b>[inferred]</b> Binary scan operator type having member <tt>T operator()(const T &a, const T &b)</tt>
 */
template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanExclusive(
    T           (&input)[LENGTH],       ///< [in] Input array
    T           (&output)[LENGTH],      ///< [out] Output array (may be aliased to \p input)
    ScanOp      scan_op,                ///< [in] Binary scan operator
    T           prefix,                 ///< [in] Prefix to seed scan with
    bool        apply_prefix = true)    ///< [in] Whether or not the calling thread should apply its prefix.  (Handy for preventing thread-0 from applying a prefix.)
{
    return ThreadScanExclusive<LENGTH>((T*) input, (T*) output, scan_op, prefix, apply_prefix);
}


template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanInclusive(
    T                   inclusive,
    T                   *input,                 ///< [in] Input array
    T                   *output,                ///< [out] Output array (may be aliased to \p input)
    ScanOp              scan_op,                ///< [in] Binary scan operator
    Int2Type<LENGTH>    /*length*/)
{
    #pragma unroll
    for (int i = 0; i < LENGTH; ++i)
    {
        inclusive = scan_op(inclusive, input[i]);
        output[i] = inclusive;
    }

    return inclusive;
}


/**
 * \brief Perform a sequential inclusive prefix scan over \p LENGTH elements of the \p input array.  The aggregate is returned.
 *
 * \tparam LENGTH     LengthT of \p input and \p output arrays
 * \tparam T          <b>[inferred]</b> The data type to be scanned.
 * \tparam ScanOp     <b>[inferred]</b> Binary scan operator type having member <tt>T operator()(const T &a, const T &b)</tt>
 */
template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanInclusive(
    T           *input,                 ///< [in] Input array
    T           *output,                ///< [out] Output array (may be aliased to \p input)
    ScanOp      scan_op)                ///< [in] Binary scan operator
{
    T inclusive = input[0];
    output[0] = inclusive;

    // Continue scan
    return ThreadScanInclusive(inclusive, input + 1, output + 1, scan_op, Int2Type<LENGTH - 1>());
}


/**
 * \brief Perform a sequential inclusive prefix scan over the statically-sized \p input array.  The aggregate is returned.
 *
 * \tparam LENGTH     <b>[inferred]</b> LengthT of \p input and \p output arrays
 * \tparam T          <b>[inferred]</b> The data type to be scanned.
 * \tparam ScanOp     <b>[inferred]</b> Binary scan operator type having member <tt>T operator()(const T &a, const T &b)</tt>
 */
template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanInclusive(
    T           (&input)[LENGTH],       ///< [in] Input array
    T           (&output)[LENGTH],      ///< [out] Output array (may be aliased to \p input)
    ScanOp      scan_op)                ///< [in] Binary scan operator
{
    return ThreadScanInclusive<LENGTH>((T*) input, (T*) output, scan_op);
}


/**
 * \brief Perform a sequential inclusive prefix scan over \p LENGTH elements of the \p input array, seeded with the specified \p prefix.  The aggregate is returned.
 *
 * \tparam LENGTH     LengthT of \p input and \p output arrays
 * \tparam T          <b>[inferred]</b> The data type to be scanned.
 * \tparam ScanOp     <b>[inferred]</b> Binary scan operator type having member <tt>T operator()(const T &a, const T &b)</tt>
 */
template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanInclusive(
    T           *input,                 ///< [in] Input array
    T           *output,                ///< [out] Output array (may be aliased to \p input)
    ScanOp      scan_op,                ///< [in] Binary scan operator
    T           prefix,                 ///< [in] Prefix to seed scan with
    bool        apply_prefix = true)    ///< [in] Whether or not the calling thread should apply its prefix.  (Handy for preventing thread-0 from applying a prefix.)
{
    T inclusive = input[0];
    if (apply_prefix)
    {
        inclusive = scan_op(prefix, inclusive);
    }
    output[0] = inclusive;

    // Continue scan
    return ThreadScanInclusive(inclusive, input + 1, output + 1, scan_op, Int2Type<LENGTH - 1>());
}


/**
 * \brief Perform a sequential inclusive prefix scan over the statically-sized \p input array, seeded with the specified \p prefix.  The aggregate is returned.
 *
 * \tparam LENGTH     <b>[inferred]</b> LengthT of \p input and \p output arrays
 * \tparam T          <b>[inferred]</b> The data type to be scanned.
 * \tparam ScanOp     <b>[inferred]</b> Binary scan operator type having member <tt>T operator()(const T &a, const T &b)</tt>
 */
template <
    int         LENGTH,
    typename    T,
    typename    ScanOp>
__device__ __forceinline__ T ThreadScanInclusive(
    T           (&input)[LENGTH],       ///< [in] Input array
    T           (&output)[LENGTH],      ///< [out] Output array (may be aliased to \p input)
    ScanOp      scan_op,                ///< [in] Binary scan operator
    T           prefix,                 ///< [in] Prefix to seed scan with
    bool        apply_prefix = true)    ///< [in] Whether or not the calling thread should apply its prefix.  (Handy for preventing thread-0 from applying a prefix.)
{
    return ThreadScanInclusive<LENGTH>((T*) input, (T*) output, scan_op, prefix, apply_prefix);
}


//@}  end member group

/** @} */       // end group UtilModule


}               // internal namespace
}               // CUB namespace
CUB_NS_POSTFIX  // Optional outer namespace(s)