1 files changed, 23 insertions, 9 deletions
diff --git a/compiler/ic/bitabs.nim b/compiler/ic/bitabs.nim
index 1f75b7759..0c9994c83 100644
--- a/compiler/ic/bitabs.nim
+++ b/compiler/ic/bitabs.nim
@@ -1,7 +1,11 @@
 ## A BiTable is a table that can be seen as an optimized pair
-## of (Table[LitId, Val], Table[Val, LitId]).
+## of `(Table[LitId, Val], Table[Val, LitId])`.
 
-import hashes, rodfiles
+import std/hashes
+import rodfiles
+
+when defined(nimPreviewSlimSystem):
+  import std/assertions
 
 type
   LitId* = distinct uint32
@@ -10,6 +14,8 @@ type
     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
 
@@ -30,12 +36,14 @@ proc mustRehash(length, counter: int): bool {.inline.} =
   result = (length * 2 < counter * 3) or (length - counter < 4)
 
 const
-  idStart = 256 ##
-  ## Ids do not start with 0 but with this value. The IR needs it.
-  ## TODO: explain why
+  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)
@@ -86,13 +94,13 @@ proc getOrIncl*[T](t: var BiTable[T]; v: T): LitId =
   t.vals.add v
 
 
-proc `[]`*[T](t: var BiTable[T]; LitId: LitId): var T {.inline.} =
-  let idx = idToIdx LitId
+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
+proc `[]`*[T](t: BiTable[T]; litId: LitId): lent T {.inline.} =
+  let idx = idToIdx litId
   assert idx < t.vals.len
   result = t.vals[idx]
 
@@ -111,6 +119,12 @@ 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]