more stuff that doesn't work

src/karaxdb/btree.nim

@@ -4,11 +4,26 @@
 ## Can also use a page manager for allocations. The page manager be used
 ## to off load pages to a file system or to send it over the wire.
 
+## Todo:
+## - Add logic to deal with the fact that keys do not have to be unique.
+## - Ranged queries
+## - Make it generic and low level
+## - Support for external nodes and a page cache
+
 const
   M = 4   # max children per B-tree node = M-1
           # (must be even and greater than 2)
   Mhalf = M div 2
 
+  SupportFullTableScan = true
+  SupportDuplicateKeys = true
+
+## Due to the fact that leaves are shared among multiple BTrees the following
+## fields in a Node are downright impossible:
+## - parent
+## - next
+## - prev
+
 type
   Key = string
   Val = string
@@ -24,6 +39,12 @@ type
     root: Node
     height: int ## height
     n: int      ## number of key-value pairs
+  CmpKind {.pure.} = enum
+    eq, le, lt, ge, gt, neq
+  Cursor = object
+    n: Node
+    i, dir: int
+    up: seq[(Node, int)]
 
 proc newBTree(): BTree = BTree(root: Node(m: 0, isInternal: false))
 
@@ -42,6 +63,86 @@ proc search(x: Node, key: Key, ht: int): Val =
       if j+1 == x.m or less(key, x.keys[j+1]):
         return search(x.links[j], key, ht-1)
 
+proc `=~`(i: int; k: CmpKind): bool =
+  ## check if the result of 'cmp' matches what was requested by 'k':
+  case k
+  of CmpKind.eq: i == 0
+  of CmpKind.le: i <= 0
+  of CmpKind.lt: i < 0
+  of CmpKind.ge: i >= 0
+  of CmpKind.gt: i > 0
+  of CmpKind.neq: i != 0
+
+proc canPrune(i: int; k: CmpKind): bool =
+  case k
+  of CmpKind.eq:
+    # we demand equality so if bigger, we can prune:
+    i > 0
+  of CmpKind.le:
+    i > 0
+  of CmpKind.lt: i >= 0
+  of CmpKind.ge: i < 0
+  of CmpKind.gt: i <= 0
+  of CmpKind.neq: i != 0
+
+proc startingPoint(x: Node; key: Key; kind: CmpKind): Cursor =
+  if x.isInternal:
+    for j in 0 ..< x.m:
+      if j+1 == x.m or cmp(key, x.keys[j+1]) =~ kind:
+        return startingPoint(x.links[j], key, kind)
+  else:
+    for j in 0 ..< x.m:
+      let cmpRes = cmp(key, x.keys[j])
+      if cmpRes =~ kind: return Cursor(n: x, i: j)
+
+proc dos(x: Node; key: Key; kind: CmpKind; withKey: proc(k: Key; v: Val)) =
+  if not x.isInternal:
+    echo "came here"
+    for j in 0 ..< x.m:
+      if cmp(key, x.keys[j]) =~ kind:
+        withKey(x.keys[j+1], x.vals[j])
+  else:
+    for j in 0 ..< x.m-1:
+      let cmpRes = cmp(key, x.keys[j+1])
+      echo "came here B ", canPrune(cmpRes, kind)
+      if not canPrune(cmpRes, kind): #cmpRes =~ kind:
+        dos(x.links[j], key, kind, withKey)
+        #if canPrune(cmpRes, kind): return
+      # XXX j+1==x.m case?
+
+
+
+proc init(x: Node): Cursor =
+  result.up = @[]
+  result.i = 0
+  var it = x
+  while it.isInternal:
+    result.up.add((it, 0))
+    it = it.links[0]
+  result.n = it
+
+proc next(c: var Cursor) =
+  assert c.n != nil
+  if c.i >= c.n.m:
+    # current leaf exhausted, pick the next one:
+    if c.up.len > 0:
+      (c.n, c.i) = c.up.pop()
+
+  inc c.i
+  var u = 1
+  while c.i > c.n.m or c.n.isInternal:
+    if c.up.len > 0:
+      (c.n, c.i) = c.up[c.up.len - u]
+    else:
+      c.n = nil
+      return
+  assert(c.n == nil or not c.n.isInternal)
+
+proc atEnd(c: Cursor): bool = c.n == nil
+
+proc getKey(c: Cursor): Key = discard
+proc getVal(c: Cursor): Val = discard
+
 proc get(t: BTree; key: Key): Val = search(t.root, key, t.height)
 
 proc copyHalf(h, result: Node; offset: int) =
@@ -187,6 +288,7 @@ proc `$`(b: BTree): string =
   result = ""
   toString(b.root, b.height, "", result)
 
+when isMainModule:
   proc main =
     var st = newBTree()
     st.put("www.cs.princeton.edu", "abc")
@@ -231,7 +333,7 @@ proc main =
     when true:
       var b1 = newBTree()
       var b2 = newBTree()
-    const iters = 60_000
+      const iters = 10 #60_000
       for i in 1..iters:
         b2 = b2.putPs($i, $(iters - i))
         b1.put($i, $(iters - i))
@@ -241,5 +343,6 @@ proc main =
           echo i, "th iteration; got ", x, ", but expected ", iters - i
       echo b2.n, " = ", b1.n
       echo b2.height, " = ", b1.height
+      dos(b1.root, "5", CmpKind.eq, proc(k: Key; v: Val) = echo("k ", k, " = ", v))
 
   main()