maheshambule commented on a change in pull request #5082: [Relay, Topi] [TF,
MXNet] Unravel Index operator
URL: https://github.com/apache/incubator-tvm/pull/5082#discussion_r394577194
##########
File path: topi/include/topi/transform.h
##########
@@ -232,6 +232,52 @@ inline Tensor reshape(const Tensor& x,
}
}
+/*!
+ * \brief Converts a flat index or array of flat indices into a tuple of
coordinate arrays
+ *
+ * \param x The input tensor having indices.
+ * \param shape The shape tensor
+ * \param name The name of the operation
+ * \param tag The tag to mark the operation
+ *
+ * \return A Tensor of coordinate arrays.
+ */
+
+inline Tensor unravel_index(const Tensor& x, const Tensor& shape, std::string
name = "T_unravel",
+ std::string tag = kInjective) {
+ auto x_shape = x->shape;
+ auto shape_shape = shape->shape;
+
+ Array<PrimExpr> oshape;
+ oshape.push_back(shape_shape[0]);
+ if (x_shape.size() != 0) {
+ oshape.push_back(x_shape[0]);
+ }
+
+ return compute(oshape,
+ [&](const Array<Var>& indices) {
+ auto i = indices[0];
+ std::vector<PrimExpr> indices_divs;
+ PrimExpr ret = 0;
+ PrimExpr cur_val = 0;
+ PrimExpr index_val = 0;
+
+ if (x_shape.size() != 0) {
+ index_val = x[indices[1]];
+ } else {
+ index_val = x();
+ }
+ indices_divs.push_back(index_val);
+ for (int v = GetConstInt(shape_shape[0]) - 1; v >= 0; --v) {
+ ret = tvm::if_then_else(i == v,
indexmod(indices_divs.back(), shape[v]), ret);
+ cur_val = indexdiv(indices_divs.back(), shape[v]);
+ indices_divs.push_back(cur_val);
Review comment:
The function in this file returns all the coordinates for a given index. In
compute definition we just want a coordinate for the current compute index and
not for all of them. I was facing issue while extracting the current coordinate
because compute index which is a Var can not be directly used to extract Expr
from an array of Exprs. I had to use if_then_else construct for that. Please
let me know if I am missing something here and if there is an easier way to
achieve this. I could have modified the existing function to meet my purposes
for example pass in the coordinate index I want to extract and return just that
coordinate. Please let me know if I should implement this.
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