nimbus-eth1/nimbus/db/kvt/kvt_delta/delta_merge.nim

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2.6 KiB
Nim

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