cuda-samples/Samples/sortingNetworks/oddEvenMergeSort.cu

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//Based on http://www.iti.fh-flensburg.de/lang/algorithmen/sortieren/networks/oemen.htm


#include <assert.h>
#include <cooperative_groups.h>

namespace cg = cooperative_groups;

#include <helper_cuda.h>
#include "sortingNetworks_common.h"
#include "sortingNetworks_common.cuh"

////////////////////////////////////////////////////////////////////////////////
// Monolithic Bacther's sort kernel for short arrays fitting into shared memory
////////////////////////////////////////////////////////////////////////////////
__global__ void oddEvenMergeSortShared(uint *d_DstKey, uint *d_DstVal,
                                       uint *d_SrcKey, uint *d_SrcVal,
                                       uint arrayLength, uint dir) {
  // Handle to thread block group
  cg::thread_block cta = cg::this_thread_block();
  // Shared memory storage for one or more small vectors
  __shared__ uint s_key[SHARED_SIZE_LIMIT];
  __shared__ uint s_val[SHARED_SIZE_LIMIT];

  // Offset to the beginning of subbatch and load data
  d_SrcKey += blockIdx.x * SHARED_SIZE_LIMIT + threadIdx.x;
  d_SrcVal += blockIdx.x * SHARED_SIZE_LIMIT + threadIdx.x;
  d_DstKey += blockIdx.x * SHARED_SIZE_LIMIT + threadIdx.x;
  d_DstVal += blockIdx.x * SHARED_SIZE_LIMIT + threadIdx.x;
  s_key[threadIdx.x + 0] = d_SrcKey[0];
  s_val[threadIdx.x + 0] = d_SrcVal[0];
  s_key[threadIdx.x + (SHARED_SIZE_LIMIT / 2)] =
      d_SrcKey[(SHARED_SIZE_LIMIT / 2)];
  s_val[threadIdx.x + (SHARED_SIZE_LIMIT / 2)] =
      d_SrcVal[(SHARED_SIZE_LIMIT / 2)];

  for (uint size = 2; size <= arrayLength; size <<= 1) {
    uint stride = size / 2;
    uint offset = threadIdx.x & (stride - 1);

    {
      cg::sync(cta);
      uint pos = 2 * threadIdx.x - (threadIdx.x & (stride - 1));
      Comparator(s_key[pos + 0], s_val[pos + 0], s_key[pos + stride],
                 s_val[pos + stride], dir);
      stride >>= 1;
    }

    for (; stride > 0; stride >>= 1) {
      cg::sync(cta);
      uint pos = 2 * threadIdx.x - (threadIdx.x & (stride - 1));

      if (offset >= stride)
        Comparator(s_key[pos - stride], s_val[pos - stride], s_key[pos + 0],
                   s_val[pos + 0], dir);
    }
  }

  cg::sync(cta);
  d_DstKey[0] = s_key[threadIdx.x + 0];
  d_DstVal[0] = s_val[threadIdx.x + 0];
  d_DstKey[(SHARED_SIZE_LIMIT / 2)] =
      s_key[threadIdx.x + (SHARED_SIZE_LIMIT / 2)];
  d_DstVal[(SHARED_SIZE_LIMIT / 2)] =
      s_val[threadIdx.x + (SHARED_SIZE_LIMIT / 2)];
}

////////////////////////////////////////////////////////////////////////////////
// Odd-even merge sort iteration kernel
// for large arrays (not fitting into shared memory)
////////////////////////////////////////////////////////////////////////////////
__global__ void oddEvenMergeGlobal(uint *d_DstKey, uint *d_DstVal,
                                   uint *d_SrcKey, uint *d_SrcVal,
                                   uint arrayLength, uint size, uint stride,
                                   uint dir) {
  uint global_comparatorI = blockIdx.x * blockDim.x + threadIdx.x;

  // Odd-even merge
  uint pos = 2 * global_comparatorI - (global_comparatorI & (stride - 1));

  if (stride < size / 2) {
    uint offset = global_comparatorI & ((size / 2) - 1);

    if (offset >= stride) {
      uint keyA = d_SrcKey[pos - stride];
      uint valA = d_SrcVal[pos - stride];
      uint keyB = d_SrcKey[pos + 0];
      uint valB = d_SrcVal[pos + 0];

      Comparator(keyA, valA, keyB, valB, dir);

      d_DstKey[pos - stride] = keyA;
      d_DstVal[pos - stride] = valA;
      d_DstKey[pos + 0] = keyB;
      d_DstVal[pos + 0] = valB;
    }
  } else {
    uint keyA = d_SrcKey[pos + 0];
    uint valA = d_SrcVal[pos + 0];
    uint keyB = d_SrcKey[pos + stride];
    uint valB = d_SrcVal[pos + stride];

    Comparator(keyA, valA, keyB, valB, dir);

    d_DstKey[pos + 0] = keyA;
    d_DstVal[pos + 0] = valA;
    d_DstKey[pos + stride] = keyB;
    d_DstVal[pos + stride] = valB;
  }
}

////////////////////////////////////////////////////////////////////////////////
// Interface function
////////////////////////////////////////////////////////////////////////////////
// Helper function
extern "C" uint factorRadix2(uint *log2L, uint L);

extern "C" void oddEvenMergeSort(uint *d_DstKey, uint *d_DstVal, uint *d_SrcKey,
                                 uint *d_SrcVal, uint batchSize,
                                 uint arrayLength, uint dir) {
  // Nothing to sort
  if (arrayLength < 2) return;

  // Only power-of-two array lengths are supported by this implementation
  uint log2L;
  uint factorizationRemainder = factorRadix2(&log2L, arrayLength);
  assert(factorizationRemainder == 1);

  dir = (dir != 0);

  uint blockCount = (batchSize * arrayLength) / SHARED_SIZE_LIMIT;
  uint threadCount = SHARED_SIZE_LIMIT / 2;

  if (arrayLength <= SHARED_SIZE_LIMIT) {
    assert(SHARED_SIZE_LIMIT % arrayLength == 0);
    oddEvenMergeSortShared<<<blockCount, threadCount>>>(
        d_DstKey, d_DstVal, d_SrcKey, d_SrcVal, arrayLength, dir);
  } else {
    oddEvenMergeSortShared<<<blockCount, threadCount>>>(
        d_DstKey, d_DstVal, d_SrcKey, d_SrcVal, SHARED_SIZE_LIMIT, dir);

    for (uint size = 2 * SHARED_SIZE_LIMIT; size <= arrayLength; size <<= 1)
      for (unsigned stride = size / 2; stride > 0; stride >>= 1) {
        // Unlike with bitonic sort, combining bitonic merge steps with
        // stride = [SHARED_SIZE_LIMIT / 2 .. 1] seems to be impossible as there
        // are dependencies between data elements crossing the SHARED_SIZE_LIMIT
        // borders
        oddEvenMergeGlobal<<<(batchSize * arrayLength) / 512, 256>>>(
            d_DstKey, d_DstVal, d_DstKey, d_DstVal, arrayLength, size, stride,
            dir);
      }
  }
}