From 12cc5dcad8d2bc37f833057c7fcffe5686031193 Mon Sep 17 00:00:00 2001
From: mratsim <mamy_github@numforge.co>
Date: Sun, 5 Aug 2018 15:07:35 +0200
Subject: [PATCH] Fix primitive types, add bitwise, shift, add, sub and
 constant time comparison

---
 hardy/bool_primitives.nim | 45 ---------------------
 hardy/ct_primitives.nim   | 84 +++++++++++++++++++++++++++++++++++++++
 hardy/datatypes.nim       |  4 +-
 3 files changed, 87 insertions(+), 46 deletions(-)
 delete mode 100644 hardy/bool_primitives.nim
 create mode 100644 hardy/ct_primitives.nim

diff --git a/hardy/bool_primitives.nim b/hardy/bool_primitives.nim
deleted file mode 100644
index 168fc4e..0000000
--- a/hardy/bool_primitives.nim
+++ /dev/null
@@ -1,45 +0,0 @@
-# Hardy
-# Copyright (c) 2018 Status Research & Development GmbH
-# Licensed and distributed under either of
-#   * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
-#   * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
-# at your option. This file may not be copied, modified, or distributed except according to those terms.
-
-import ./datatypes
-
-# ################################
-#
-# Constant-time boolean primitives
-#
-# ################################
-
-# The main challenge is to prevent conditional branch/jump
-# in the generated assembly.
-#
-# Note:
-#   let x = if true: 1 else: 2
-#
-# does not guarantee a constant-time conditional move
-# The compiler might introduce branching.
-
-# These primitives are internal to Hardy.
-# We don't want to pollute unsuspecting users
-# with `not` and `-` on unsigned ints
-
-func high*(T: typedesc[HardBase]): T {.inline.}=
-  result = not T(0)
-
-func `not`*[T: HardBase](ctl: HardBool[T]): HardBool[T] {.inline.}=
-  ## Negate a constant-time boolean
-  result = ctl xor 1.T
-
-func `-`*(x: HardBase): HardBase {.inline.}=
-  ## Unary minus returns the two-complement representation
-  ## of an unsigned integer
-  const max = high(type x)
-  result = (max xor x) + 1
-
-func mux*[T: HardBase](ctl: HardBool[T], x, y: T): T {.inline.}=
-  ## Returns x if ctl == 1
-  ## else returns y
-  result = y xor (-ctl.HardBase and (x xor y))
diff --git a/hardy/ct_primitives.nim b/hardy/ct_primitives.nim
new file mode 100644
index 0000000..79a13c3
--- /dev/null
+++ b/hardy/ct_primitives.nim
@@ -0,0 +1,84 @@
+# Hardy
+# Copyright (c) 2018 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+import ./datatypes
+
+# #########################
+#
+# Constant-time primitives
+#
+# #########################
+
+# The main challenge is to prevent conditional branch/jump
+# in the generated assembly.
+#
+# Note:
+#   let x = if true: 1 else: 2
+#
+# does not guarantee a constant-time conditional move
+# The compiler might introduce branching.
+
+# These primitives are distinct type and internal to Hardy.
+# We don't want to pollute unsuspecting users
+# with `not` and `-` on unsigned ints
+
+# #################################################################
+# Hard base borrows
+# We should use {.borrow.} instead of {.magic.} but pending:
+#    - https://github.com/nim-lang/Nim/pull/8531
+#    - https://github.com/nim-lang/Nim/issues/4121 (can be workaround with #8531)
+
+func high*(T: typedesc[HardBase]): T {.inline.}=
+  not T(0)
+
+
+func `and`*[T: HardBase](x, y: T): T {.magic: "BitandI".}
+func `or`*[T: HardBase](x, y: T): T {.magic: "BitorI".}
+func `xor`*[T: HardBase](x, y: T): T {.magic: "BitxorI".}
+func `not`*[T: HardBase](x: T): T {.magic: "BitnotI".}
+func `+`*[T: HardBase](x, y: T): T {.magic: "AddU".}
+func `-`*[T: HardBase](x, y: T): T {.magic: "SubU".}
+func `shr`*[T: HardBase](x: T, y: SomeInteger): T {.magic: "ShrI".}
+func `shl`*[T: HardBase](x: T, y: SomeInteger): T {.magic: "ShlI".}
+
+# #################################################################
+
+func `not`*(ctl: HardBool): HardBool {.inline.}=
+  ## Negate a constant-time boolean
+  result = ctl xor 1
+
+func `-`*(x: HardBase): HardBase {.inline.}=
+  ## Unary minus returns the two-complement representation
+  ## of an unsigned integer
+  {.emit:"`result` = -`x`;".}
+
+func mux*[T: HardBase](ctl: HardBool[T], x, y: T): T {.inline.}=
+  ## Multiplexer / selector
+  ## Returns x if ctl == 1
+  ## else returns y
+  result = y xor (-ctl.T and (x xor y))
+
+func `!=`*[T: HardBase](x, y: T): HardBool[T] {.inline.}=
+  const msb = T.sizeof * 8 - 1
+  let z = x xor y
+  result = (type result)((z or -z) shr msb)
+
+func `==`*[T: HardBase](x, y: T): HardBool[T] {.inline.}=
+  result = not(x != y)
+
+func `<`*[T: HardBase](x, y: T): HardBool[T] {.inline.}=
+  const msb = T.sizeof * 8 - 1
+  result = (type result)(
+    (
+      x xor (
+        (x xor y) or ((x - y) xor y)
+      )
+    ) shr msb
+  )
+
+func `<=`*[T: HardBase](x, y: T): HardBool[T] {.inline.}=
+  (y < x) xor 1
diff --git a/hardy/datatypes.nim b/hardy/datatypes.nim
index 7115afb..673c74d 100644
--- a/hardy/datatypes.nim
+++ b/hardy/datatypes.nim
@@ -6,7 +6,9 @@
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
 type
-  HardBase* = SomeUnsignedInt or byte
+  BaseUint* = SomeUnsignedInt or byte
+
+  HardBase*[T: BaseUint] = distinct T
 
   HardBool*[T: HardBase] = range[T(0)..T(1)]
     ## To avoid the compiler replacing bitwise boolean operations