remove a condition that table size must be passed as power of 2 (#14926)

* remove a condition that table size must be passed as power of 2
* remove power-of-2 condition from sets and sharedtables
* remove power-of-2 condition from deques
* use 'correctSize' for both branches
* prettify changelog.md and fix typos
* add a changelog entry
* fix double-call of 'right-size'
* fix the same thing in sets.nim
* introduce a new internal proc `slotsNeeded`

Deprecate the public proc `rightSize`, which is not needed anymore.
Now it is an identity function, allowing the old code to work
correctly and without extra allocations.

7 files changed, 29 insertions, 92 deletions

diff --git a/lib/pure/collections/deques.nim b/lib/pure/collections/deques.nim
index d096874a3..8150563cc 100644
--- a/lib/pure/collections/deques.nim
+++ b/lib/pure/collections/deques.nim
@@ -67,9 +67,9 @@ const
   defaultInitialSize* = 4
 
 template initImpl(result: typed, initialSize: int) =
-  assert isPowerOfTwo(initialSize)
-  result.mask = initialSize-1
-  newSeq(result.data, initialSize)
+  let correctSize = nextPowerOfTwo(initialSize)
+  result.mask = correctSize-1
+  newSeq(result.data, correctSize)
 
 template checkIfInitialized(deq: typed) =
   when compiles(defaultInitialSize):
@@ -82,11 +82,6 @@ proc initDeque*[T](initialSize: int = 4): Deque[T] =
   ## Optionally, the initial capacity can be reserved via `initialSize`
   ## as a performance optimization.
   ## The length of a newly created deque will still be 0.
-  ##
-  ## ``initialSize`` must be a power of two (default: 4).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_.
   result.initImpl(initialSize)
 
 proc len*[T](deq: Deque[T]): int {.inline.} =
diff --git a/lib/pure/collections/hashcommon.nim b/lib/pure/collections/hashcommon.nim
index e998145e7..336dbc07d 100644
--- a/lib/pure/collections/hashcommon.nim
+++ b/lib/pure/collections/hashcommon.nim
@@ -30,17 +30,23 @@ proc nextTry(h, maxHash: Hash): Hash {.inline.} =
   result = (h + 1) and maxHash
 
 proc mustRehash[T](t: T): bool {.inline.} =
+  # If this is changed, make sure to synchronize it with `slotsNeeded` below
   assert(t.dataLen > t.counter)
   result = (t.dataLen * 2 < t.counter * 3) or (t.dataLen - t.counter < 4)
 
-proc rightSize*(count: Natural): int {.inline.} =
+proc slotsNeeded(count: Natural): int {.inline.} =
+  # Make sure to synchronize with `mustRehash` above
+  result = nextPowerOfTwo(count * 3 div 2 + 4)
+
+proc rightSize*(count: Natural): int {.inline, deprecated: "Deprecated since 1.4.0".} =
+  ## **Deprecated since Nim v1.4.0**, it is not needed anymore
+  ## because picking the correct size is done internally.
+  ##
   ## Return the value of ``initialSize`` to support ``count`` items.
   ##
   ## If more items are expected to be added, simply add that
   ## expected extra amount to the parameter before calling this.
-  #
-  # Make sure to synchronize with `mustRehash`
-  result = nextPowerOfTwo(count * 3 div 2 + 4)
+  result = count
 
 template rawGetKnownHCImpl() {.dirty.} =
   if t.dataLen == 0:
diff --git a/lib/pure/collections/setimpl.nim b/lib/pure/collections/setimpl.nim
index d798cbcb3..20da6b6c2 100644
--- a/lib/pure/collections/setimpl.nim
+++ b/lib/pure/collections/setimpl.nim
@@ -16,12 +16,12 @@ template dataLen(t): untyped = len(t.data)
 include hashcommon
 
 template initImpl(s: typed, size: int) =
-  assert isPowerOfTwo(size)
+  let correctSize = slotsNeeded(size)
   when s is OrderedSet:
     s.first = -1
     s.last = -1
   s.counter = 0
-  newSeq(s.data, size)
+  newSeq(s.data, correctSize)
 
 template rawInsertImpl() {.dirty.} =
   if data.len == 0:
diff --git a/lib/pure/collections/sets.nim b/lib/pure/collections/sets.nim
index 2b270c2cb..b019da2a7 100644
--- a/lib/pure/collections/sets.nim
+++ b/lib/pure/collections/sets.nim
@@ -94,11 +94,6 @@ include setimpl
 proc init*[A](s: var HashSet[A], initialSize = defaultInitialSize) =
   ## Initializes a hash set.
   ##
-  ## The `initialSize` parameter needs to be a power of two (default: 64).
-  ## If you need to accept runtime values for this, you can use
-  ## `math.nextPowerOfTwo proc <math.html#nextPowerOfTwo,int>`_ or
-  ## `rightSize proc <#rightSize,Natural>`_ from this module.
-  ##
   ## Starting from Nim v0.20, sets are initialized by default and it is
   ## not necessary to call this function explicitly.
   ##
@@ -222,7 +217,7 @@ proc toHashSet*[A](keys: openArray[A]): HashSet[A] =
     assert len(b) == 5
     ## b == {'a', 'b', 'c', 'd', 'r'}
 
-  result = initHashSet[A](rightSize(keys.len))
+  result = initHashSet[A](keys.len)
   for key in items(keys): result.incl(key)
 
 iterator items*[A](s: HashSet[A]): A =
@@ -628,11 +623,6 @@ template forAllOrderedPairs(yieldStmt: untyped) {.dirty.} =
 proc init*[A](s: var OrderedSet[A], initialSize = defaultInitialSize) =
   ## Initializes an ordered hash set.
   ##
-  ## The `initialSize` parameter needs to be a power of two (default: 64).
-  ## If you need to accept runtime values for this, you can use
-  ## `math.nextPowerOfTwo proc <math.html#nextPowerOfTwo,int>`_ or
-  ## `rightSize proc <#rightSize,Natural>`_ from this module.
-  ##
   ## Starting from Nim v0.20, sets are initialized by default and it is
   ## not necessary to call this function explicitly.
   ##
@@ -685,7 +675,7 @@ proc toOrderedSet*[A](keys: openArray[A]): OrderedSet[A] =
     assert len(b) == 5
     ## b == {'a', 'b', 'r', 'c', 'd'} # different than in HashSet
 
-  result = initOrderedSet[A](rightSize(keys.len))
+  result = initOrderedSet[A](keys.len)
   for key in items(keys): result.incl(key)
 
 proc contains*[A](s: OrderedSet[A], key: A): bool =
@@ -980,7 +970,7 @@ when isMainModule and not defined(release):
 
     block toSeqAndString:
       var a = toHashSet([2, 7, 5])
-      var b = initHashSet[int](rightSize(a.len))
+      var b = initHashSet[int](a.len)
       for x in [2, 7, 5]: b.incl(x)
       assert($a == $b)
       #echo a
@@ -1098,20 +1088,6 @@ when isMainModule and not defined(release):
       b.incl(2)
       assert b.len == 1
 
-    block:
-      type FakeTable = object
-        dataLen: int
-        counter: int
-        countDeleted: int
-
-      var t: FakeTable
-      for i in 0 .. 32:
-        var s = rightSize(i)
-        t.dataLen = s
-        t.counter = i
-        doAssert s > i and not mustRehash(t),
-          "performance issue: rightSize() will not elide enlarge() at: " & $i
-
     block missingOrExcl:
       var s = toOrderedSet([2, 3, 6, 7])
       assert s.missingOrExcl(4) == true
diff --git a/lib/pure/collections/sharedtables.nim b/lib/pure/collections/sharedtables.nim
index abef89507..cbd922db7 100644
--- a/lib/pure/collections/sharedtables.nim
+++ b/lib/pure/collections/sharedtables.nim
@@ -207,15 +207,11 @@ proc len*[A, B](t: var SharedTable[A, B]): int =
   withLock t:
     result = t.counter
 
-proc init*[A, B](t: var SharedTable[A, B], initialSize = 64) =
+proc init*[A, B](t: var SharedTable[A, B], initialSize = 32) =
   ## creates a new hash table that is empty.
   ##
   ## This proc must be called before any other usage of `t`.
-  ##
-  ## `initialSize` needs to be a power of two. If you need to accept runtime
-  ## values for this you could use the ``nextPowerOfTwo`` proc from the
-  ## `math <math.html>`_ module or the ``rightSize`` proc from this module.
-  assert isPowerOfTwo(initialSize)
+  let initialSize = slotsNeeded(initialSize)
   t.counter = 0
   t.dataLen = initialSize
   t.data = cast[KeyValuePairSeq[A, B]](allocShared0(
diff --git a/lib/pure/collections/tableimpl.nim b/lib/pure/collections/tableimpl.nim
index 47c14af93..b9d7c70d9 100644
--- a/lib/pure/collections/tableimpl.nim
+++ b/lib/pure/collections/tableimpl.nim
@@ -121,12 +121,12 @@ template ctAnd(a, b): bool =
   else: false
 
 template initImpl(result: typed, size: int) =
+  let correctSize = slotsNeeded(size)
   when ctAnd(declared(SharedTable), type(result) is SharedTable):
-    init(result, size)
+    init(result, correctSize)
   else:
-    assert isPowerOfTwo(size)
     result.counter = 0
-    newSeq(result.data, size)
+    newSeq(result.data, correctSize)
     when compiles(result.first):
       result.first = -1
       result.last = -1
diff --git a/lib/pure/collections/tables.nim b/lib/pure/collections/tables.nim
index a969a4c5d..cf864c640 100644
--- a/lib/pure/collections/tables.nim
+++ b/lib/pure/collections/tables.nim
@@ -239,7 +239,7 @@ type
     ## <#newTable,int>`_.
 
 const
-  defaultInitialSize* = 64
+  defaultInitialSize* = 32
 
 # ------------------------------ helpers ---------------------------------
 
@@ -288,12 +288,6 @@ proc enlarge[A, B](t: var Table[A, B]) =
 proc initTable*[A, B](initialSize = defaultInitialSize): Table[A, B] =
   ## Creates a new hash table that is empty.
   ##
-  ## ``initialSize`` must be a power of two (default: 64).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_ or the `rightSize proc<#rightSize,Natural>`_
-  ## from this module.
-  ##
   ## Starting from Nim v0.20, tables are initialized by default and it is
   ## not necessary to call this function explicitly.
   ##
@@ -335,7 +329,7 @@ proc toTable*[A, B](pairs: openArray[(A, B)]): Table[A, B] =
     let b = toTable(a)
     assert b == {'a': 5, 'b': 9}.toTable
 
-  result = initTable[A, B](rightSize(pairs.len))
+  result = initTable[A, B](pairs.len)
   for key, val in items(pairs): result[key] = val
 
 proc `[]`*[A, B](t: Table[A, B], key: A): B =
@@ -780,12 +774,6 @@ iterator allValues*[A, B](t: Table[A, B]; key: A): B =
 proc newTable*[A, B](initialSize = defaultInitialSize): <//>TableRef[A, B] =
   ## Creates a new ref hash table that is empty.
   ##
-  ## ``initialSize`` must be a power of two (default: 64).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_ or the `rightSize proc<#rightSize,Natural>`_
-  ## from this module.
-  ##
   ## See also:
   ## * `newTable proc<#newTable,openArray[]>`_ for creating a `TableRef`
   ##   from a collection of `(key, value)` pairs
@@ -1260,12 +1248,6 @@ template forAllOrderedPairs(yieldStmt: untyped) {.dirty.} =
 proc initOrderedTable*[A, B](initialSize = defaultInitialSize): OrderedTable[A, B] =
   ## Creates a new ordered hash table that is empty.
   ##
-  ## ``initialSize`` must be a power of two (default: 64).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_ or the `rightSize proc<#rightSize,Natural>`_
-  ## from this module.
-  ##
   ## Starting from Nim v0.20, tables are initialized by default and it is
   ## not necessary to call this function explicitly.
   ##
@@ -1309,7 +1291,7 @@ proc toOrderedTable*[A, B](pairs: openArray[(A, B)]): OrderedTable[A, B] =
     let b = toOrderedTable(a)
     assert b == {'a': 5, 'b': 9}.toOrderedTable
 
-  result = initOrderedTable[A, B](rightSize(pairs.len))
+  result = initOrderedTable[A, B](pairs.len)
   for key, val in items(pairs): result[key] = val
 
 proc `[]`*[A, B](t: OrderedTable[A, B], key: A): B =
@@ -1771,12 +1753,6 @@ iterator mvalues*[A, B](t: var OrderedTable[A, B]): var B =
 proc newOrderedTable*[A, B](initialSize = defaultInitialSize): <//>OrderedTableRef[A, B] =
   ## Creates a new ordered ref hash table that is empty.
   ##
-  ## ``initialSize`` must be a power of two (default: 64).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_ or the `rightSize proc<#rightSize,Natural>`_
-  ## from this module.
-  ##
   ## See also:
   ## * `newOrderedTable proc<#newOrderedTable,openArray[]>`_ for creating
   ##   an `OrderedTableRef` from a collection of `(key, value)` pairs
@@ -1803,7 +1779,7 @@ proc newOrderedTable*[A, B](pairs: openArray[(A, B)]): <//>OrderedTableRef[A, B]
     let b = newOrderedTable(a)
     assert b == {'a': 5, 'b': 9}.newOrderedTable
 
-  result = newOrderedTable[A, B](rightSize(pairs.len))
+  result = newOrderedTable[A, B](pairs.len)
   for key, val in items(pairs): result.add(key, val)
 
 
@@ -2251,12 +2227,6 @@ proc inc*[A](t: var CountTable[A], key: A, val: Positive = 1)
 proc initCountTable*[A](initialSize = defaultInitialSize): CountTable[A] =
   ## Creates a new count table that is empty.
   ##
-  ## ``initialSize`` must be a power of two (default: 64).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_ or the `rightSize proc<#rightSize,Natural>`_
-  ## from this module.
-  ##
   ## Starting from Nim v0.20, tables are initialized by default and it is
   ## not necessary to call this function explicitly.
   ##
@@ -2269,7 +2239,7 @@ proc initCountTable*[A](initialSize = defaultInitialSize): CountTable[A] =
 proc toCountTable*[A](keys: openArray[A]): CountTable[A] =
   ## Creates a new count table with every member of a container ``keys``
   ## having a count of how many times it occurs in that container.
-  result = initCountTable[A](rightSize(keys.len))
+  result = initCountTable[A](keys.len)
   for key in items(keys): result.inc(key)
 
 proc `[]`*[A](t: CountTable[A], key: A): int =
@@ -2617,12 +2587,6 @@ proc inc*[A](t: CountTableRef[A], key: A, val = 1)
 proc newCountTable*[A](initialSize = defaultInitialSize): <//>CountTableRef[A] =
   ## Creates a new ref count table that is empty.
   ##
-  ## ``initialSize`` must be a power of two (default: 64).
-  ## If you need to accept runtime values for this you could use the
-  ## `nextPowerOfTwo proc<math.html#nextPowerOfTwo,int>`_ from the
-  ## `math module<math.html>`_ or the `rightSize proc<#rightSize,Natural>`_
-  ## from this module.
-  ##
   ## See also:
   ## * `newCountTable proc<#newCountTable,openArray[A]>`_ for creating
   ##   a `CountTableRef` from a collection
@@ -2634,7 +2598,7 @@ proc newCountTable*[A](initialSize = defaultInitialSize): <//>CountTableRef[A] =
 proc newCountTable*[A](keys: openArray[A]): <//>CountTableRef[A] =
   ## Creates a new ref count table with every member of a container ``keys``
   ## having a count of how many times it occurs in that container.
-  result = newCountTable[A](rightSize(keys.len))
+  result = newCountTable[A](keys.len)
   for key in items(keys): result.inc(key)
 
 proc `[]`*[A](t: CountTableRef[A], key: A): int =