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;
}
}
}