template <int BLOCK_SIZE> __global__ void
matrixMulCUDA_3_2w1w(float* C, float* A, float* B, int wA, int wB)
{
	// Block index
	int bx = blockIdx.x;
	int by = blockIdx.y;
	// Thread index
	int tx = threadIdx.x;
	int ty = threadIdx.y;

	for (int x = 1; x <= 2; x++)
	{
		// Index of the first sub-matrix of A processed by the block
		int aBegin = wA * BLOCK_SIZE * by;
		// Index of the last sub-matrix of A processed by the block
		int aEnd = aBegin + wA - 1;
		// Step size used to iterate through the sub-matrices of A
		int aStep = BLOCK_SIZE;
		// Index of the first sub-matrix of B processed by the block
		int bBegin = BLOCK_SIZE * bx;
		// Step size used to iterate through the sub-matrices of B
		int bStep = BLOCK_SIZE * wB;
		// Csub is used to store the element of the block sub-matrix
		// that is computed by the thread
		float Csub = 0;
		// Loop over all the sub-matrices of A and B
		// required to compute the block sub-matrix
		for (int a = aBegin, b = bBegin;
			a <= aEnd;
			a += aStep, b += bStep)
		{
			// Declaration of the shared memory array As used to
			// store the sub-matrix of A
			__shared__ float As[BLOCK_SIZE / 2][BLOCK_SIZE];
			// Declaration of the shared memory array Bs used to
			// store the sub-matrix of B
			__shared__ float Bs[BLOCK_SIZE][BLOCK_SIZE];
			// Load the matrices from device memory
			// to shared memory; each thread loads
			// one element of each matrix
			if (x == 1)
			{
				if (ty < BLOCK_SIZE / 2)
				{
					As[ty][tx] = A[a + wA * ty + tx];
				}
				Bs[ty][tx] = B[b + wB * ty + tx];
			}
			else if (x == 2)
			{
				if (ty >= BLOCK_SIZE / 2)
				{
					As[ty][tx] = A[a + wA * ty + tx];
				}
			}
			// Synchronize to make sure the matrices are loaded
			__syncthreads();
			// Multiply the two matrices together;
			// 2 thread computes one element
			// of the block sub-matrix
#pragma unroll
			for (int k = 0; k < BLOCK_SIZE / 2; k++)
			{
				if (ty < BLOCK_SIZE / 2)
				{
					Csub += As[ty][k] * Bs[k][tx];
				}
				else
				{
					Csub += As[ty][k + BLOCK_SIZE / 2] * Bs[k + BLOCK_SIZE / 2][tx];
				}
			}
			// Synchronize to make sure that the preceding
			// computation is done before loading two new
			// sub-matrices of A and B in the next iteration
			__syncthreads();
		}
		// Write the block sub-matrix to device memory;
		// each thread writes one element
		int c = wB * BLOCK_SIZE * by + BLOCK_SIZE * bx;
		if (ty < BLOCK_SIZE / 2 && x == 1)
		{
			C[c + wB * ty + tx] += Csub;
		}
		else if (ty >= BLOCK_SIZE / 2 && x == 2)
		{
			C[c + wB * ty + tx] += Csub;
		}
	}
}