71 lines
2.6 KiB
Nim
71 lines
2.6 KiB
Nim
# nimbus-eth1
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# Copyright (c) 2023-2024 Status Research & Development GmbH
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# Licensed under either of
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# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
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# http://www.apache.org/licenses/LICENSE-2.0)
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# * MIT license ([LICENSE-MIT](LICENSE-MIT) or
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# http://opensource.org/licenses/MIT)
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# at your option. This file may not be copied, modified, or distributed
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# except according to those terms.
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import
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std/tables,
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../kvt_desc
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# ------------------------------------------------------------------------------
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# Private functions
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# ------------------------------------------------------------------------------
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proc layersMergeOnto(src: LayerRef; trg: var LayerObj) =
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for (key,val) in src.sTab.pairs:
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trg.sTab[key] = val
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# ------------------------------------------------------------------------------
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# Public functions
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# ------------------------------------------------------------------------------
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proc deltaMerge*(
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upper: LayerRef; # Think of `top`, `nil` is ok
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modUpperOk: bool; # May re-use/modify `upper`
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lower: LayerRef; # Think of `balancer`, `nil` is ok
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modLowerOk: bool; # May re-use/modify `lower`
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): LayerRef =
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## Merge argument `upper` into the `lower` filter instance.
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##
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## Note that the namimg `upper` and `lower` indicate that the filters are
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## stacked and the database access is `upper -> lower -> backend`.
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##
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if lower.isNil:
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# Degenerate case: `upper` is void
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result = upper
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elif upper.isNil:
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# Degenerate case: `lower` is void
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result = lower
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elif modLowerOk:
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# Can modify `lower` which is the prefered action mode but applies only
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# in cases where the `lower` argument is not shared.
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layersMergeOnto(upper, lower[])
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result = lower
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elif not modUpperOk:
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# Cannot modify any argument layers.
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result = LayerRef(sTab: lower.sTab)
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layersMergeOnto(upper, result[])
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else:
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# Otherwise avoid copying some tables by modifyinh `upper`. This is not
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# completely free as the merge direction changes to merging the `lower`
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# layer up into the higher prioritised `upper` layer (note that the `lower`
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# argument filter is read-only.) Here again, the `upper` argument must not
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# be a shared layer/filter.
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for (key,val) in lower.sTab.pairs:
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if not upper.sTab.hasKey(key):
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upper.sTab[key] = val
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result = upper
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# ------------------------------------------------------------------------------
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# End
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# ------------------------------------------------------------------------------
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