Update slice algorithm steps for strides

Author: fdwr

index.bs

@@ -8838,19 +8838,27 @@ partial dictionary MLOpSupportLimits {
     1. If [=MLGraphBuilder/validating operand=] with [=this=] and |input| returns false, then [=exception/throw=] a {{TypeError}}.
     1. If any of |sizes|'s [=list/items=] are 0, then [=exception/throw=] a {{TypeError}}.
     1. If |starts|'s [=list/size=] and |sizes|'s [=list/size=] are not both equal to |input|'s [=MLOperand/rank=], then [=exception/throw=] a {{TypeError}}.
+    1. Let |strides| be a new [=/list=].
     1. If |options|.{{MLSliceOptions/strides}} [=map/exists=]:
-        1. If |options|.{{MLSliceOptions/strides}}'s [=list/size=] is not equal to |input|'s [=MLOperand/rank=], then [=exception/throw=] a {{TypeError}}.
-    1. [=list/For each=] |index| in [=the range=] 0 to |input|'s [=MLOperand/rank=], exclusive:
+        1. Set |strides| to |options|.{{MLSliceOptions/strides}}.
+        1. If |strides|'s [=list/size=] is not equal to |input|'s [=MLOperand/rank=], then [=exception/throw=] a {{TypeError}}.
+    1. Let |inputShape| be |input|'s [=MLOperand/shape=] and |inputRank| be |input|'s [=MLOperand/rank=].
+    1. Let |outputShape| be a new [=/list=].
+    1. [=list/For each=] |index| in [=the range=] 0 to |inputRank|, exclusive:
         1. If |sizes|[|index|] is 0, then [=exception/throw=] a {{TypeError}}.
 
             Issue(391): If 0-size dimensions are allowed, revise these steps.
 
-        1. If |starts|[|index|] is greater than or equal to |input|'s [=MLOperand/shape=][|index|], then [=exception/throw=] a {{TypeError}}.
-        1. If |starts|[|index|] + |sizes|[|index|] is greater than |input|'s [=MLOperand/shape=][|index|], then [=exception/throw=] a {{TypeError}}.
-        1. If |options|.{{MLSliceOptions/strides}} [=map/exists=]:
-            1. If |options|.{{MLSliceOptions/strides}}[|index|] is less than 1, then [=exception/throw=] a {{TypeError}}.
+        1. If |starts|[|index|] is greater than |inputShape|[|index|], then [=exception/throw=] a {{TypeError}}.
+        1. If |starts|[|index|] + |sizes|[|index|] is greater than |inputShape|[|index|], then [=exception/throw=] a {{TypeError}}.
+        1. Let |stride| be |strides|[|index|] if it is not empty, or 1 otherwise:
+        1. If |stride| is less than 1, then [=exception/throw=] a {{TypeError}}.
+        1. Let |outputSizeRoundingExcess| be 1 if |inputShape|[|index|] % |stride| != 0, or 0 otherwise.
+        1. Let |outputSize| be |inputShape|[|index|] / |stride| + |outputSizeRoundingExcess|
+        1. [=list/Append=] |outputSize| to |outputShape|.
+    1. Let |outputDesc| be the result of [=creating an MLOperandDescriptor=] given |input|'s [=MLOperand/dataType=] and |outputShape|.
     1. *Make graph connections:*
-        1. Let |output| be the result of [=copying an MLOperand=] given |input|.
+        1. Let |output| be the result of [=creating an MLOperand=] given |outputDesc|.
         1. Let |operator| be an [=operator=] for the "slice" operation, given |starts|, |sizes|, and |options|.
         1. Set |output|.{{MLOperand/[[operator]]}} to |operator|.
         1. Set |operator|'s [=operator/input=] to |input|.