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## A BiTable is a table that can be seen as an optimized pair
## of `(Table[LitId, Val], Table[Val, LitId])`.
import std/hashes
import rodfiles
when defined(nimPreviewSlimSystem):
import std/assertions
type
LitId* = distinct uint32
BiTable*[T] = object
vals: seq[T] # indexed by LitId
keys: seq[LitId] # indexed by hash(val)
proc initBiTable*[T](): BiTable[T] = BiTable[T](vals: @[], keys: @[])
proc nextTry(h, maxHash: Hash): Hash {.inline.} =
result = (h + 1) and maxHash
template maxHash(t): untyped = high(t.keys)
template isFilled(x: LitId): bool = x.uint32 > 0'u32
proc `$`*(x: LitId): string {.borrow.}
proc `<`*(x, y: LitId): bool {.borrow.}
proc `<=`*(x, y: LitId): bool {.borrow.}
proc `==`*(x, y: LitId): bool {.borrow.}
proc hash*(x: LitId): Hash {.borrow.}
proc len*[T](t: BiTable[T]): int = t.vals.len
proc mustRehash(length, counter: int): bool {.inline.} =
assert(length > counter)
result = (length * 2 < counter * 3) or (length - counter < 4)
const
idStart = 1
template idToIdx(x: LitId): int = x.int - idStart
proc hasLitId*[T](t: BiTable[T]; x: LitId): bool =
let idx = idToIdx(x)
result = idx >= 0 and idx < t.vals.len
proc enlarge[T](t: var BiTable[T]) =
var n: seq[LitId]
newSeq(n, len(t.keys) * 2)
swap(t.keys, n)
for i in 0..high(n):
let eh = n[i]
if isFilled(eh):
var j = hash(t.vals[idToIdx eh]) and maxHash(t)
while isFilled(t.keys[j]):
j = nextTry(j, maxHash(t))
t.keys[j] = move n[i]
proc getKeyId*[T](t: BiTable[T]; v: T): LitId =
let origH = hash(v)
var h = origH and maxHash(t)
if t.keys.len != 0:
while true:
let litId = t.keys[h]
if not isFilled(litId): break
if t.vals[idToIdx t.keys[h]] == v: return litId
h = nextTry(h, maxHash(t))
return LitId(0)
proc getOrIncl*[T](t: var BiTable[T]; v: T): LitId =
let origH = hash(v)
var h = origH and maxHash(t)
if t.keys.len != 0:
while true:
let litId = t.keys[h]
if not isFilled(litId): break
if t.vals[idToIdx t.keys[h]] == v: return litId
h = nextTry(h, maxHash(t))
# not found, we need to insert it:
if mustRehash(t.keys.len, t.vals.len):
enlarge(t)
# recompute where to insert:
h = origH and maxHash(t)
while true:
let litId = t.keys[h]
if not isFilled(litId): break
h = nextTry(h, maxHash(t))
else:
setLen(t.keys, 16)
h = origH and maxHash(t)
result = LitId(t.vals.len + idStart)
t.keys[h] = result
t.vals.add v
proc `[]`*[T](t: var BiTable[T]; litId: LitId): var T {.inline.} =
let idx = idToIdx litId
assert idx < t.vals.len
result = t.vals[idx]
proc `[]`*[T](t: BiTable[T]; litId: LitId): lent T {.inline.} =
let idx = idToIdx litId
assert idx < t.vals.len
result = t.vals[idx]
proc hash*[T](t: BiTable[T]): Hash =
## as the keys are hashes of the values, we simply use them instead
var h: Hash = 0
for i, n in pairs t.keys:
h = h !& hash((i, n))
result = !$h
proc store*[T](f: var RodFile; t: BiTable[T]) =
storeSeq(f, t.vals)
storeSeq(f, t.keys)
proc load*[T](f: var RodFile; t: var BiTable[T]) =
loadSeq(f, t.vals)
loadSeq(f, t.keys)
proc sizeOnDisc*(t: BiTable[string]): int =
result = 4
for x in t.vals:
result += x.len + 4
result += t.keys.len * sizeof(LitId)
when isMainModule:
var t: BiTable[string]
echo getOrIncl(t, "hello")
echo getOrIncl(t, "hello")
echo getOrIncl(t, "hello3")
echo getOrIncl(t, "hello4")
echo getOrIncl(t, "helloasfasdfdsa")
echo getOrIncl(t, "hello")
echo getKeyId(t, "hello")
echo getKeyId(t, "none")
for i in 0 ..< 100_000:
discard t.getOrIncl($i & "___" & $i)
for i in 0 ..< 100_000:
assert t.getOrIncl($i & "___" & $i).idToIdx == i + 4
echo "begin"
echo t.vals.len
echo t.vals[0]
echo t.vals[1004]
echo "middle"
var tf: BiTable[float]
discard tf.getOrIncl(0.4)
discard tf.getOrIncl(16.4)
discard tf.getOrIncl(32.4)
echo getKeyId(tf, 32.4)
var f2 = open("testblah.bin", fmWrite)
echo store(f2, tf)
f2.close
var f1 = open("testblah.bin", fmRead)
var t2: BiTable[float]
echo f1.load(t2)
echo t2.vals.len
echo getKeyId(t2, 32.4)
echo "end"
f1.close
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