From 97fbe56353ac46d6812b459d42a154dcd6ebbe6b Mon Sep 17 00:00:00 2001
From: mratsim <mamy_github@numforge.co>
Date: Wed, 25 Apr 2018 15:41:59 +0200
Subject: [PATCH] Add most significant bit and isNegative proc

---
 src/private/as_words.nim       | 29 ++++++++++++++++++++++-------
 src/private/bithacks.nim       | 24 +++++++++++++++++++++++-
 src/private/int_comparison.nim | 30 +++++++-----------------------
 3 files changed, 52 insertions(+), 31 deletions(-)

diff --git a/src/private/as_words.nim b/src/private/as_words.nim
index 09f16cc..599fc93 100644
--- a/src/private/as_words.nim
+++ b/src/private/as_words.nim
@@ -30,6 +30,28 @@ proc optim(x: NimNode): NimNode =
   else:
     error "Unreachable path reached"
 
+proc isUint(x: NimNode): static[bool] =
+  if eqIdent(x, "uint64"):   true
+  elif eqIdent(x, "uint32"): true
+  elif eqIdent(x, "uint16"): true
+  elif eqIdent(x, "uint8"):  true
+  else: false
+
+macro most_significant_word*(x: IntImpl): untyped =
+
+  let optim_type = optim(x)
+  if optim_type.isUint:
+    result = quote do:
+      cast[`optim_type`](`x`)
+  else:
+    when system.cpuEndian == littleEndian:
+      let size = getSize(x)
+      let msw_pos = size - 1
+    else:
+      let msw_pos = 0
+    result = quote do:
+      cast[`optim_type`](`x`)[`msw_pos`]
+
 proc replaceNodes(ast: NimNode, replacing: NimNode, to_replace: NimNode): NimNode =
   # Args:
   #   - The full syntax tree
@@ -53,13 +75,6 @@ proc replaceNodes(ast: NimNode, replacing: NimNode, to_replace: NimNode): NimNod
       return rTree
   result = inspect(ast)
 
-proc isUint(x: NimNode): static[bool] =
-  if eqIdent(x, "uint64"):   true
-  elif eqIdent(x, "uint32"): true
-  elif eqIdent(x, "uint16"): true
-  elif eqIdent(x, "uint8"):  true
-  else: false
-
 macro asWords*[T](n: UintImpl[T], ignoreEndianness: static[bool], loopBody: untyped): untyped =
   ## Iterates over n, as an array of words.
   ## Input:
diff --git a/src/private/bithacks.nim b/src/private/bithacks.nim
index 0caaa67..ad33a92 100644
--- a/src/private/bithacks.nim
+++ b/src/private/bithacks.nim
@@ -7,7 +7,7 @@
 #
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
-import  ./datatypes, stdlib_bitops
+import  ./datatypes, stdlib_bitops, as_words
 export stdlib_bitops
 
 # We reuse bitops from Nim standard lib, and expand it for multi-precision int.
@@ -24,3 +24,25 @@ func countLeadingZeroBits*(n: UintImpl): int {.inline.} =
   result =  if hi_clz == maxHalfRepr:
               n.lo.countLeadingZeroBits + maxHalfRepr
             else: hi_clz
+
+func msb*[T: SomeInteger](n: T): T =
+  ## Returns the most significant bit of an integer.
+
+  when T is int64 or (T is int and sizeof(int) == 8):
+    type UInt = uint64
+  elif T is int32 or (T is int and sizeof(int) == 4):
+    type Uint = uint32
+  elif T is int16:
+    type Uint = uint16
+  elif T is int8:
+    type Uint = uint8
+  else:
+    type Uint = T
+
+  const msb_pos = sizeof(T) * 8 - 1
+  result = T(cast[Uint](n) shr msb_pos)
+
+func msb*(n: IntImpl): auto =
+  ## Returns the most significant bit of an arbitrary precision integer.
+
+  result = msb most_significant_word(n)
diff --git a/src/private/int_comparison.nim b/src/private/int_comparison.nim
index 8087682..d747a06 100644
--- a/src/private/int_comparison.nim
+++ b/src/private/int_comparison.nim
@@ -7,34 +7,18 @@
 #
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
-import  ./datatypes, ./as_words, ./uint_comparison
+import  ./datatypes, ./bithacks, ./as_words,
+        ./bithacks
 
-func isZero*(n: SomeUnsignedInt): bool {.inline.} =
+func isZero*(n: SomeSignedInt): bool {.inline.} =
   n == 0
 
-func isZero*(n: UintImpl): bool {.inline.} =
+func isZero*(n: IntImpl): bool {.inline.} =
   asWords(n, ignoreEndianness = true):
     if n != 0:
       return false
   return true
 
-func `<`*(x, y: UintImpl): bool {.inline.}=
-  # Lower comparison for multi-precision integers
-  asWordsZip(x, y, ignoreEndianness = false):
-    if x != y:
-      return x < y
-  return false # they're equal
-
-func `==`*(x, y: UintImpl): bool {.inline.}=
-  # Equal comparison for multi-precision integers
-  asWordsZip(x, y, ignoreEndianness = true):
-    if x != y:
-      return false
-  return true # they're equal
-
-func `<=`*(x, y: UintImpl): bool {.inline.}=
-  # Lower or equal comparison for multi-precision integers
-  asWordsZip(x, y, ignoreEndianness = false):
-    if x != y:
-      return x < y
-  return true # they're equal
+func isNegative*(n: IntImpl): bool {.inline.} =
+  ## Returns true if a number is negative:
+  n.msb.bool