diff --git a/config.nims b/config.nims
index c3b9fc0..824ce34 100644
--- a/config.nims
+++ b/config.nims
@@ -1,5 +1,5 @@
---threads: on
---d: release
---opt: speed
---passC: -flto
---passL: -flto
\ No newline at end of file
+# --threads: on
+# --d: release
+# --opt: speed
+# --passC: -flto
+# --passL: -flto
\ No newline at end of file
diff --git a/fixedseq.nim b/fixedseq.nim
index 4bdc88c..9961f2b 100644
--- a/fixedseq.nim
+++ b/fixedseq.nim
@@ -124,7 +124,7 @@ proc shuffle*(s: var FixedSeq, r: var Rand) =
 
 
 proc moveSubstack*(src, dst: var FixedSeq; start: Natural) =
-  var count: typeof(src.last) = 0 # have to track this separately apparently
+  var count: FixedSeq.Pointer = 0 # have to track this separately apparently
   for idx in start .. src.last:
     swap(src.data[idx], dst.data[dst.last + 1 + count])
     inc count
@@ -133,7 +133,7 @@ proc moveSubstack*(src, dst: var FixedSeq; start: Natural) =
 
 
 proc moveSubstackPre*(src, dst: var FixedSeq; start: Natural) =
-  let ssLen = typeof(src.last)(src.last - start + 1) # length of substack
+  let ssLen = FixedSeq.Pointer(src.last - start + 1) # length of substack
   for i in countdown(dst.last, 0):
     swap(dst.data[i], dst.data[i + ssLen])
 
@@ -144,3 +144,5 @@ proc moveSubstackPre*(src, dst: var FixedSeq; start: Natural) =
 
   dst.last += ssLen
   src.last -= ssLen
+
+include shiftstack
diff --git a/game.nim b/game.nim
index f6e8d8a..598f665 100644
--- a/game.nim
+++ b/game.nim
@@ -33,7 +33,7 @@ proc abbrev*(c: Color): char =
   result = colorAbbrevs[c]
 
 
-proc `$`*(s: ColorStack): string =
+proc `$`*[T](s: FixedSeq[T, Color, int8]): string =
   result.add("St@[")
   for i, color in s:
     result.add($color)
diff --git a/shiftstack.nim b/shiftstack.nim
new file mode 100644
index 0000000..7be8b57
--- /dev/null
+++ b/shiftstack.nim
@@ -0,0 +1,182 @@
+# optimized bit-shifting versions of the FixedSequence substack operations
+import bitops, macros
+import game
+
+
+macro show(expr: untyped) =
+  let node = expr.toStrLit
+  quote do:
+    echo `node`, " => ", `expr`
+
+
+proc getMasks(): (array[9, uint64], array[9, uint64]) =
+  # on little-endian architectures, casting an array[8, Color]
+  # to uint64 effectively reverses it. So we switch these masks
+  # so that we can refer to them consistently.
+  let 
+    left = [
+      0'u64,
+      0xff_00_00_00_00_00_00_00'u64,
+      0xff_ff_00_00_00_00_00_00'u64,
+      0xff_ff_ff_00_00_00_00_00'u64,
+      0xff_ff_ff_ff_00_00_00_00'u64,
+      0xff_ff_ff_ff_ff_00_00_00'u64,
+      0xff_ff_ff_ff_ff_ff_00_00'u64,
+      0xff_ff_ff_ff_ff_ff_ff_00'u64,
+      0xff_ff_ff_ff_ff_ff_ff_ff'u64,
+    ]
+    right = [
+      0'u64,
+      0x00_00_00_00_00_00_00_ff'u64,
+      0x00_00_00_00_00_00_ff_ff'u64,
+      0x00_00_00_00_00_ff_ff_ff'u64,
+      0x00_00_00_00_ff_ff_ff_ff'u64,
+      0x00_00_00_ff_ff_ff_ff_ff'u64,
+      0x00_00_ff_ff_ff_ff_ff_ff'u64,
+      0x00_ff_ff_ff_ff_ff_ff_ff'u64,
+      0xff_ff_ff_ff_ff_ff_ff_ff'u64,
+    ]
+  when cpuEndian == bigEndian:
+    result = (left, right)
+  when cpuEndian == littleEndian:
+    result = (right, left)
+
+
+type ShiftStack = FixedSeq[8, Color, int8]
+const (masksLeft, masksRight) = getMasks()
+
+
+template `shl`(a: array[8, Color], offset: Natural): array[8, Color] =
+  when cpuEndian == bigEndian:
+    cast[array[8, Color]](cast[uint64](a) shl (offset * 8))
+  when cpuEndian == littleEndian: # direction is reversed
+    cast[array[8, Color]](cast[uint64](a) shr (offset * 8))
+
+
+template `shr`(a: array[8, Color], offset: Natural): array[8, Color] =
+  when cpuEndian == bigEndian:
+    cast[array[8, Color]](cast[uint64](a) shr (offset * 8))
+  when cpuEndian == littleEndian:
+    cast[array[8, Color]](cast[uint64](a) shl (offset * 8))
+
+
+template `and`(a: array[8, Color], mask: uint64): array[8, Color] =
+  cast[array[8, Color]](cast[uint64](a) and mask)
+
+
+template `or`(a: array[8, Color], mask: uint64): array[8, Color] =
+  cast[array[8, Color]](cast[uint64](a) or mask)
+
+
+template `or`(a: array[8, Color], mask: array[8, Color]): array[8, Color] =
+  cast[array[8, Color]](cast[uint64](a) or cast[uint64](mask))
+
+
+import strutils # remove later
+proc moveSubstack*(src, dst: var ShiftStack; start: Natural) =
+  # shift the source stack to position the substack above its final resting place
+  # offset is the length of the destination stack, minus the number of items NOT being moved
+  # number of items not being moved is the same as the start index
+  var substack: array[8, Color] 
+  # if dst.len == start, no shift necessary, otherwise:
+  if dst.len > start:
+    substack = src.data shr (dst.len - start)
+  elif dst.len < start:
+    substack = src.data shl (start)
+  # next, mask the source data to present only the items being moved
+  # dst.len of 0 corresponds to last mask in masksRight, aka masksRight[^1]
+  substack = substack and masksRight[^(dst.len + 1)]
+  # then combine
+  dst.data = dst.data or substack
+  # then git rid of the moved items from the source stack
+  src.data = src.data and masksLeft[start]
+  # a little bookkeeping
+  let ssLen = int8(src.len - start)
+  src.last -= ssLen
+  dst.last += ssLen
+
+
+proc moveSubstackPre*(src, dst: var ShiftStack; start: Natural) =
+  let ssLen = int8(src.len - start)
+  # shift the destination stack to make room for the new items
+  dst.data = dst.data shr ssLen
+  # shift source stack to line up the substack with its final resting place
+  let substack = src.data shl start
+  # combine
+  dst.data = dst.data or substack
+  # get rid of the moved items
+  src.data = src.data and masksLeft[start]
+  # more bookkeeping
+  src.last -= ssLen
+  dst.last += ssLen
+
+
+proc `==`[T1: FixedSeq, T2: FixedSeq](a: T1, b: T2): bool =
+  if a.len != b.len:
+    return false
+  for i in 0 ..< a.len:
+    if a.data[i] != b.data[i]:
+      return false
+  return true
+
+
+proc testMove[T1, T2: FixedSeq](a1, a2: var T1; b1, b2: var T2; i: Natural): bool =
+  let (orig_a1, orig_a2) = (a1, a2)
+  let (orig_b1, orig_b2) = (b1, b2)
+  a1.moveSubstackPre(a2, i)
+  b1.moveSubstackPre(b2, i)
+  if a1 != b1 or a2 != b2:
+    echo "Failed!"
+    show orig_b1
+    show orig_b2
+    echo "<< move ", i, ">>"
+    show b1
+    show b2
+    return false
+  return true
+
+
+when isMainModule:
+  var c1 = initFixedSeq(5, Color, int8)
+  var c2 = initFixedSeq(5, Color, int8)
+
+  var s1: ShiftStack
+  s1.initFixedSeq
+  var s2: ShiftStack
+  s2.initFixedSeq
+
+  # s1.add(cPurple)
+  # s1.add(cRed)
+  # s1.add(cYellow)
+  # s1.add(cBlue)
+  # s1.add(cGreen)
+
+  # show s1
+  # show s2
+  # echo "<<move 4>>"
+  # s1.moveSubstack(s2, 4)
+  # show s1
+  # show s2
+
+  import random
+  randomize()
+  var r = initRand(rand(int64))
+  var success = true
+
+  for n in 1 .. 10000:
+    if c1.len > 0:
+      let i = r.rand(c1.high)
+      if not testMove(c1, c2, s1, s2, i):
+        success = false
+        echo "Failed after ", n, " iterations."
+        break
+
+    if c2.len > 0:
+      let j = r.rand(c2.high)
+      if not testMove(c2, c1, s2, s1, j):
+        success = false
+        echo "Failed after ", n, " iterations."
+        break
+
+  if success:
+    echo "Success."