/extra/cuda/demos/prefix-sum/prefix-sum.cu
http://github.com/abeaumont/factor · Cuda · 103 lines · 79 code · 24 blank · 0 comment · 12 complexity · bf0aea855a8422e5cfd479c316dce00c MD5 · raw file
- #include <stdio.h>
- #include <stdlib.h>
- #include <cuda_runtime.h>
- static const int LOG_BANK_COUNT = 4;
- static inline __device__ __host__ unsigned shared_offset(unsigned i)
- {
- return i + (i >> LOG_BANK_COUNT);
- }
- static inline __device__ __host__ unsigned offset_a(unsigned offset, unsigned i)
- {
- return shared_offset(offset * (2*i + 1) - 1);
- }
- static inline __device__ __host__ unsigned offset_b(unsigned offset, unsigned i)
- {
- return shared_offset(offset * (2*i + 2) - 1);
- }
- static inline __device__ __host__ unsigned lpot(unsigned x)
- {
- --x; x |= x>>1; x|=x>>2; x|=x>>4; x|=x>>8; x|=x>>16; return ++x;
- }
- template<typename T>
- __global__ void prefix_sum_block(T *in, T *out, unsigned n)
- {
- extern __shared__ T temp[];
- int idx = threadIdx.x;
- int blocksize = blockDim.x;
- temp[shared_offset(idx )] = (idx < n) ? in[idx ] : 0;
- temp[shared_offset(idx + blocksize)] = (idx + blocksize < n) ? in[idx + blocksize] : 0;
- int offset, d;
- for (offset = 1, d = blocksize; d > 0; d >>= 1, offset <<= 1) {
- __syncthreads();
- if (idx < d) {
- unsigned a = offset_a(offset, idx), b = offset_b(offset, idx);
- temp[b] += temp[a];
- }
- }
- if (idx == 0) temp[shared_offset(blocksize*2 - 1)] = 0;
- for (d = 1; d <= blocksize; d <<= 1) {
- offset >>= 1;
- __syncthreads();
- if (idx < d) {
- unsigned a = offset_a(offset, idx), b = offset_b(offset, idx);
- unsigned t = temp[a];
- temp[a] = temp[b];
- temp[b] += t;
- }
- }
- __syncthreads();
- if (idx < n) out[idx ] = temp[shared_offset(idx )];
- if (idx + blocksize < n) out[idx + blocksize] = temp[shared_offset(idx + blocksize)];
- }
- template<typename T>
- void prefix_sum(T *in, T *out, unsigned n)
- {
- char *device_values;
- unsigned n_lpot = lpot(n);
- size_t n_pitch;
- cudaError_t error = cudaMallocPitch((void**)&device_values, &n_pitch, sizeof(T)*n, 2);
- if (error != 0) {
- printf("error %u allocating width %lu height %u\n", error, sizeof(T)*n, 2);
- exit(1);
- }
- cudaMemcpy(device_values, in, sizeof(T)*n, cudaMemcpyHostToDevice);
- prefix_sum_block<<<1, n_lpot/2, shared_offset(n_lpot)*sizeof(T)>>>
- ((T*)device_values, (T*)(device_values + n_pitch), n);
- cudaMemcpy(out, device_values + n_pitch, sizeof(T)*n, cudaMemcpyDeviceToHost);
- cudaFree(device_values);
- }
- int main()
- {
- sranddev();
- static unsigned in_values[1024], out_values[1024];
- for (int i = 0; i < 1024; ++i)
- in_values[i] = rand() >> 21;
- prefix_sum(in_values, out_values, 1024);
- for (int i = 0; i < 1024; ++i)
- printf("%5d => %5d\n", in_values[i], out_values[i]);
- return 0;
- }