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authorDominic Symes <dominic.symes@arm.com>2021-01-13 12:02:51 +0000
committerDominic Symes <dominic.symes@arm.com>2021-01-13 12:07:52 +0000
commit488a29344419bd2e4402fc6394d43c123548e1ec (patch)
tree44f295d6b58d230e8305b55334053476c865d233
parente5d22a77300643f0a3013ad40ccd2b5b76788b42 (diff)
downloadspecification-488a29344419bd2e4402fc6394d43c123548e1ec.tar.gz
SCATTER: Clarify behaviour
This clarifies that repeated updates to the same output index are not permitted in TOSA SCATTER. Change-Id: Ib188a434d0d4ad4742ee37373491c8a53d501bf0 Signed-off-by: Dominic Symes <dominic.symes@arm.com>
-rw-r--r--chapters/scatter_gather.adoc13
1 files changed, 12 insertions, 1 deletions
diff --git a/chapters/scatter_gather.adoc b/chapters/scatter_gather.adoc
index e1be77f..65c0fe3 100644
--- a/chapters/scatter_gather.adoc
+++ b/chapters/scatter_gather.adoc
@@ -55,6 +55,8 @@ for_each(0<=n<N, 0<=w<W, 0<=c<C) {
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.
*Arguments:*
@@ -75,18 +77,27 @@ None
[source,c]
----
+
+// The following array is used to check compliance that an output position
+// is modified at most once.
+bool 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) {
value_t value = tensor_read<value_t>(values_in, [N,K,C], [n,k,c])
tensor_write<value_t>(values_out, [N,K,C], [n, k, c], value)
+ output_modified[n,k,c]=false;
}
-// Now perform the SCATTER operation, writing to the positions from the indices tensor
+
+// 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])
assert(0<=k && k<K)
+ assert(output_modified[n,k,c]==false);
value_t value = tensor_read<value_t>(input, [N,W,C], [n,w,c])
tensor_write<value_t>(values_out, [N,K,C], [n, k, c], value)
+ output_modified[n,k,c]=true;
}
----