121 lines
3.2 KiB
Nim
121 lines
3.2 KiB
Nim
# The hash table implementation for string interning
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import strformat
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const tableMaxLoad = 0.75
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const tableInitSize = 8
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type
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EntryStatus = enum
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esNil, esAlive, esTombstone
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Entry*[U, V] = object
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entryStatus: EntryStatus
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key: U
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value: V
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Table*[U, V] = object
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count: int
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cap: int
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entries: ptr UncheckedArray[Entry[U, V]]
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proc newTable*[U, V]: Table[U, V] =
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result.cap = 0
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result.count = 0
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proc free*[U, V](tbl: var Table[U, V]) =
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if tbl.entries != nil:
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dealloc(tbl.entries)
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proc isNil[U, V](entry: ptr Entry[U, V]): bool {.inline.} =
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entry[].entryStatus == esNil
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proc isTombstone[U, V](entry: ptr Entry[U, V]): bool {.inline.} =
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entry[].entryStatus == esTombstone
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proc isAlive[U, V](entry: ptr Entry[U, V]): bool {.inline.} =
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entry[].entryStatus == esAlive
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proc findEntry[U, V](entries: ptr UncheckedArray[Entry[U, V]], cap: int, key: U): ptr Entry[U, V] =
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var index = key.hash() mod cap # TODO replace mod with sth better
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var tombstone: ptr Entry[U, V] = nil
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while true:
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let entry: ptr Entry[U, V] = entries[index].addr # TODO: check the performance impact of this line
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if entry.isNil():
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return if tombstone != nil: tombstone else: entry
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elif entry.isTombstone(): # TODO: optimalization: case statement
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if tombstone == nil:
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tombstone = entry
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elif entry[].key == key:
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return entry
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index = (index + 1) mod cap # TODO replace mod with sth better
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proc grow[U, V](tbl: var Table[U, V]): int {.inline.} =
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## Calculates the new capacity
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if tbl.cap > 0:
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tbl.cap * 2
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else:
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tableInitSize
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proc adjustCapacity[U, V](tbl: var Table[U, V], newcap: int) =
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let entries: ptr UncheckedArray[Entry[U, V]] = cast[ptr UncheckedArray[Entry[U, V]]](alloc0(newcap * sizeof(Entry[U, V])))
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tbl.count = 0
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for i in countup(0, tbl.cap-1):
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let entry = tbl.entries[i]
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if entry.entryStatus == esAlive:
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var dest = findEntry(entries, newcap, entry.key)
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dest[].key = entry.key
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dest[].value = entry.value
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dest[].entryStatus = esAlive
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tbl.count.inc
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if tbl.entries != nil:
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dealloc(tbl.entries)
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tbl.entries = entries
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tbl.cap = newcap
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proc tableSet*[U, V](tbl: var Table[U, V], key: U, val: V): bool =
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## Returns false if new value is entered
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## True if the value entered already existed and is overwritten
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if tbl.count + 1 > int(tbl.cap.float * tableMaxLoad):
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let cap = tbl.grow()
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tbl.adjustCapacity(cap)
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let entry: ptr Entry[U, V] = findEntry(tbl.entries, tbl.cap, key)
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let status = entry[].entryStatus
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if status == esNil:
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tbl.count.inc
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elif status == esAlive:
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result = true
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entry[].key = key
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entry[].value = val
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entry[].entryStatus = esAlive
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proc tableGet*[U, V](tbl: Table[U, V], key: U, val: var V): bool =
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## Returns false if not in table
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## Returns true if in the table, sets value to val
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if tbl.count == 0:
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return false
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let entry = findEntry(tbl.entries, tbl.cap, key)
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if not entry.isAlive():
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return false
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val = entry[].value
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return true
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proc tableDelete*[U, V](tbl: Table[U, V], key: U): bool =
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if tbl.count == 0:
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return false
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let entry = findEntry(tbl.entries, tbl.cap, key)
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if not entry.isAlive():
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return false
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entry[].entryStatus = esTombstone
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return true
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