*: add the ability to stride window access #377
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This commit adds support for windowing of tensors in the existing index notation DSL. For example: ``` A(i, j) = B(i(1, 4), j) * C(i, j(5, 10)) ``` causes `B` to be windowed along its first mode, and `C` to be windowed along its second mode. In this commit any mix of windowed and non-windowed modes are supported, along with windowing the same tensor in different ways in the same expression. The windowing expressions correspond to the `:` operator to slice dimensions in `numpy`. Currently, only windowing by integers is supported. Windowing is achieved by tying windowing information to particular `Iterator` objects, as these are created for each `Tensor`-`IndexVar` pair. When iterating over an `Iterator` that may be windowed, extra steps are taken to either generate an index into the windowed space, or to recover an index from a point in the windowed space.
This commit extends the windowing syntax to include an optional third parameter to a window expression on an index variable: ``` a(i) = b(i(0, n, 5 /* stride */)) ``` This stride parameters means that the window should be accessed along the provided stride, which defaults to 1. Striding is implemented with a similar idea as windowing, where coordinates in the stride are mapped to a canonical index space of `[0,n)`. For compressed modes, coordinates that don't match the stride are skipped.
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This commit extends the windowing syntax to include an optional third
parameter to a window expression on an index variable:
This stride parameters means that the window should be accessed along
the provided stride, which defaults to 1.
Striding is implemented with a similar idea as windowing, where
coordinates in the stride are mapped to a canonical index space of
[0,n).For compressed modes, coordinates that don't match the stride are
skipped.
Depends on #372.