Is there any OpenCL library having Prefix Sum?

Hi,

I need a Prefix Sum implementation. If I implement it myself, I cannot make sure it is the best implementation so far.

Is there any OpenCL library for that?

Thanks!

There are some :smiley:
Take one:

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/*
 * ScanLargeArrays : Scan is done for each block and the sum of each
 * block is stored in separate array (sumBuffer). SumBuffer is scanned
 * and results are added to every value of next corresponding block to
 * compute the scan of a large array.(not limited to 2*MAX_GROUP_SIZE)
 * Scan uses a balanced tree algorithm. See Belloch, 1990 "Prefix Sums
 * and Their Applications"
 * @param output output data 
 * @param input  input data
 * @param block  local memory used in the kernel
 * @param sumBuffer  sum of blocks
 * @param length length of the input data
 */
#ifndef TYPE
#error TYPE Type not set
#endif

//#define __kernel
//#define __global const
//#define __local const
//#define TYPE uint
//#define uint int

__kernel
void
blockAddition(__global TYPE* input, __global TYPE* output)
{
	int globalId = get_global_id(0);
	int groupId = get_group_id(0);
	int localId = get_local_id(0);

	__local TYPE value[1];

	/* Only 1 thread of a group will read from global buffer */
	if (localId == 0)
	{
		value[0] = input[groupId];
	}
	barrier (CLK_LOCAL_MEM_FENCE);

	output[globalId] += value[0];
}

__kernel
void
prefixSum(__global TYPE *output, __global TYPE *input, __local TYPE *block,
		const uint length)
{
	int tid = get_local_id(0);

	int offset = 1;

	/* Cache the computational window in shared memory */
	block[2 * tid] = input[2 * tid];
	block[2 * tid + 1] = input[2 * tid + 1];

	/* build the sum in place up the tree */
	for (int d = length >> 1; d > 0; d >>= 1)
	{
		barrier (CLK_LOCAL_MEM_FENCE);

		if (tid < d)
		{
			int ai = offset * (2 * tid + 1) - 1;
			int bi = offset * (2 * tid + 2) - 1;

			block[bi] += block[ai];
		}
		offset *= 2;
	}

	/* scan back down the tree */

	/* clear the last element */
	if (tid == 0)
	{
		block[length - 1] = 0;
	}

	/* traverse down the tree building the scan in the place */
	for (int d = 1; d < length; d *= 2)
	{
		offset >>= 1;
		barrier (CLK_LOCAL_MEM_FENCE);

		if (tid < d)
		{
			int ai = offset * (2 * tid + 1) - 1;
			int bi = offset * (2 * tid + 2) - 1;

			TYPE t = block[ai];
			block[ai] = block[bi];
			block[bi] += t;
		}
	}

	barrier (CLK_LOCAL_MEM_FENCE);

	/*write the results back to global memory */
	output[2 * tid] = block[2 * tid];
	output[2 * tid + 1] = block[2 * tid + 1];
}

__kernel
void
ScanLargeArrays(__global TYPE *output, __global TYPE *input,
		__local TYPE *block, // Size : block_size
		const uint block_size,// size of block
		const uint length,// no of elements
		__global TYPE *sumBuffer)// sum of blocks

{
	int tid = get_local_id(0);
	int gid = get_global_id(0);
	int bid = get_group_id(0);

	int offset = 1;

	/* Cache the computational window in shared memory */
	block[2 * tid] = input[2 * gid];
	block[2 * tid + 1] = input[2 * gid + 1];

	/* build the sum in place up the tree */
	for (int d = block_size >> 1; d > 0; d >>= 1)
	{
		barrier (CLK_LOCAL_MEM_FENCE);

		if (tid < d)
		{
			int ai = offset * (2 * tid + 1) - 1;
			int bi = offset * (2 * tid + 2) - 1;

			block[bi] += block[ai];
		}
		offset *= 2;
	}

	barrier (CLK_LOCAL_MEM_FENCE);

	int group_id = get_group_id(0);

	/* store the value in sum buffer before making it to 0 */
	sumBuffer[bid] = block[block_size - 1];

	barrier(CLK_LOCAL_MEM_FENCE | CLK_GLOBAL_MEM_FENCE);

	/* scan back down the tree */

	/* clear the last element */
	block[block_size - 1] = 0;

	/* traverse down the tree building the scan in the place */
	for (int d = 1; d < block_size; d *= 2)
	{
		offset >>= 1;
		barrier(CLK_LOCAL_MEM_FENCE);

		if (tid < d)
		{
			int ai = offset * (2 * tid + 1) - 1;
			int bi = offset * (2 * tid + 2) - 1;

			TYPE t = block[ai];
			block[ai] = block[bi];
			block[bi] += t;
		}
	}

	barrier(CLK_LOCAL_MEM_FENCE);

	/*write the results back to global memory */

	if (group_id == 0)
	{
		output[2 * gid] = block[2 * tid];
		output[2 * gid + 1] = block[2 * tid + 1];
	}
	else
	{
		output[2 * gid] = block[2 * tid];
		output[2 * gid + 1] = block[2 * tid + 1];
	}

}

__kernel
void
ScanLargeArrays_init(__global TYPE *output, __global TYPE *input,
		__local TYPE *block, // Size : block_size
		const uint block_size,// size of block
		const uint length,// no of elements
		__global TYPE *sumBuffer)// sum of blocks

{
	int tid = get_local_id(0);
	int gid = get_global_id(0);
	int bid = get_group_id(0);

	int offset = 1;

	/* Cache the computational window in shared memory */
	TYPE val1 = input[2 * gid];
	TYPE val2 = input[2 * gid + 1];
	//!=0xffffff means value is valid so mask it with 1
	block[2 * tid] = (val1 < 0xffffffff) ? 1 : 0;
	block[2 * tid + 1] = (val2 < 0xffffffff) ? 1 : 0;

	/* build the sum in place up the tree */
	for (int d = block_size >> 1; d > 0; d >>= 1)
	{
		barrier (CLK_LOCAL_MEM_FENCE);

		if (tid < d)
		{
			int ai = offset * (2 * tid + 1) - 1;
			int bi = offset * (2 * tid + 2) - 1;

			block[bi] += block[ai];
		}
		offset *= 2;
	}

	barrier (CLK_LOCAL_MEM_FENCE);

	int group_id = get_group_id(0);

	/* store the value in sum buffer before making it to 0 */
	sumBuffer[bid] = block[block_size - 1];

	barrier(CLK_LOCAL_MEM_FENCE | CLK_GLOBAL_MEM_FENCE);

	/* scan back down the tree */

	/* clear the last element */
	block[block_size - 1] = 0;

	/* traverse down the tree building the scan in the place */
	for (int d = 1; d < block_size; d *= 2)
	{
		offset >>= 1;
		barrier(CLK_LOCAL_MEM_FENCE);

		if (tid < d)
		{
			int ai = offset * (2 * tid + 1) - 1;
			int bi = offset * (2 * tid + 2) - 1;

			TYPE t = block[ai];
			block[ai] = block[bi];
			block[bi] += t;
		}
	}

	barrier(CLK_LOCAL_MEM_FENCE);

	/*write the results back to global memory */

	if (group_id == 0)
	{
		output[2 * gid] = block[2 * tid];
		output[2 * gid + 1] = block[2 * tid + 1];
	}
	else
	{
		output[2 * gid] = block[2 * tid];
		output[2 * gid + 1] = block[2 * tid + 1];
	}

}







Oh, thank you very much!

Is it working well?
Post here if any problems i m interesting in the stuff as well

I am learning it right now.

In what order do I call those kernels?

Thanks again!