| // |
| // This confidential and proprietary software may be used only as |
| // authorised by a licensing agreement from ARM Limited |
| // (C) COPYRIGHT 2020-2021 ARM Limited |
| // ALL RIGHTS RESERVED |
| // The entire notice above must be reproduced on all authorised |
| // copies and copies may only be made to the extent permitted |
| // by a licensing agreement from ARM Limited. |
| |
| === Scatter/Gather Operators |
| |
| ==== GATHER |
| |
| Generate a tensor for which each element in the output is a subtensor of the values tensor based on the indices. |
| N is the number of batches, W the number of indices in each batch, K the range of each index and C the number data channels for each index. |
| |
| include::{generated}/operators/GATHER.adoc[] |
| |
| [source,c++] |
| ---- |
| for_each(0 <= n < N, 0 <= w < W, 0 <= c < C) { |
| index_t k = tensor_read<index_t>(indices, [N,W], [n,w]); |
| REQUIRE(0 <= k && k < K); |
| in_out_t value = tensor_read<in_out_t>(values, [N,K,C], [n,k,c]); |
| tensor_write<in_out_t>(output, [N,W,C], [n,w,c], value); |
| } |
| ---- |
| |
| ==== SCATTER |
| |
| The values_out tensor is set to the values_in tensor with data modified as follows: data from the input tensor is inserted at the positions specified by the indices tensor. |
| N is the number of batches, W the number of indices in each batch, K the range of each index and C the number data channels for each index. |
| It is not permitted to repeat the same output index within a single SCATTER operation and so each output index occurs at most once. |
| In use cases that require multiple updates to the same output position, these must be decomposed into multiple SCATTER operations. |
| |
| include::{generated}/operators/SCATTER.adoc[] |
| |
| [source,c++] |
| ---- |
| |
| // The following array is used to check compliance that an output position |
| // is modified at most once. |
| bool_t output_modified[N,K,C]; |
| |
| // Copy the values_in tensor to the values_out tensor. |
| // Values not written by the scatter operation are unchanged in the output. |
| for_each(0 <= n < N, 0 <= k < K, 0 <= c < C) { |
| in_out_t value = tensor_read<in_out_t>(values_in, [N,K,C], [n,k,c]); |
| tensor_write<in_out_t>(values_out, [N,K,C], [n, k, c], value); |
| output_modified[n,k,c]=false; |
| } |
| |
| // Now perform the SCATTER operation, modifying the positions from the indices tensor |
| for_each(0 <= n < N, 0 <= w < W, 0 <= c < C) { |
| index_t k = tensor_read<index_t>(indices, [N,W], [n,w]); |
| REQUIRE(0 <= k && k < K); |
| REQUIRE(output_modified[n,k,c] == false); |
| in_out_t value = tensor_read<in_out_t>(input, [N,W,C], [n,w,c]); |
| tensor_write<in_out_t>(values_out, [N,K,C], [n, k, c], value); |
| output_modified[n,k,c] = true; |
| } |
| ---- |