From bfb0825721fe83390a77324a0d669235a0958358 Mon Sep 17 00:00:00 2001
From: Emery Hemingway <ehmry@posteo.net>
Date: Fri, 4 Jun 2021 11:39:52 +0200
Subject: [PATCH] Bigint fixes

* Native and big integer comparison
* Refuse to serialize negative big ints for now
---
 src/preserves.nim       | 32 +++++++++++++++++++++-----------
 tests/test_integers.nim |  4 ++--
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/src/preserves.nim b/src/preserves.nim
index d9eaad8..d98eeaa 100644
--- a/src/preserves.nim
+++ b/src/preserves.nim
@@ -55,7 +55,12 @@ proc `<`(x, y: string | seq[byte]): bool =
 
 proc `<`*[T](x, y: Preserve[T]): bool =
   if x.kind != y.kind:
-    result = x.kind < y.kind
+    if x.kind == pkSignedInteger and y.kind == pkBigInteger:
+      result = x.int < y.bigint
+    elif x.kind == pkBigInteger and y.kind == pkSignedInteger:
+      result = x.bigint < y.int
+    else:
+      result = x.kind < y.kind
   else:
     case x.kind
     of pkBoolean:
@@ -126,6 +131,7 @@ proc hash*[T](prs: Preserve[T]): Hash =
   of pkSignedInteger:
     h = h !& hash(prs.int)
   of pkBigInteger:
+    h = h !& hash(prs.bigint.flags)
     h = h !& hash(prs.bigint)
   of pkString:
     h = h !& hash(prs.string)
@@ -265,12 +271,13 @@ proc write*[T](str: Stream; prs: Preserve[T]) =
           inc(bitCount)
       var byteCount = (bitCount + 8) div 8
       str.write(0xa0'u8 or (byteCount - 1))
-      proc write(n: uint8, i: BiggestInt) =
+      proc write(n: uint8; i: BiggestInt) =
         if n > 0:
           write(n.pred, i shr 8)
           str.write(i.uint8)
       write(byteCount, prs.int)
   of pkBigInteger:
+    doAssert(Negative notin prs.bigint.flags, "negative big integers not implemented")
     var bytes = newSeqOfCap[uint8](prs.bigint.limbs.len * 4)
     var begun = false
     for i in countdown(prs.bigint.limbs.high, 0):
@@ -285,8 +292,6 @@ proc write*[T](str: Stream; prs: Preserve[T]) =
     else:
       str.write(0xb0'u8)
       str.writeVarint(bytes.len)
-    if Negative in prs.bigint.flags:
-      bytes[0] = uint8(- bytes[0].int8)
     str.write(cast[string](bytes))
   of pkString:
     str.write(0xb1'u8)
@@ -364,7 +369,7 @@ proc parsePreserve*(s: Stream): Preserve[void] =
     let len = s.readVarint()
     result.symbol = s.readStr(len)
   of 0xb4:
-    result = Preserve[void](kind: pkRecord #[, label: s.parsePreserve()]#)
+    result = Preserve[void](kind: pkRecord)
     while s.peekUint8() != endMarker:
       result.record.add(s.parsePreserve())
     discard s.readUint8()
@@ -389,12 +394,9 @@ proc parsePreserve*(s: Stream): Preserve[void] =
     discard s.readUint8()
   of 0xb0:
     let len = s.readVarint()
-    let initial = s.readInt8()
-    result = Preserve[void](kind: pkBigInteger, bigint: initBigInt(initial))
-    for _ in 2..len:
+    result = Preserve[void](kind: pkBigInteger)
+    for _ in 1..len:
       result.bigint = (result.bigint shl 8) + s.readUint8().int32
-    if initial < 0:
-      result.bigint.flags = {Negative}
   else:
     case 0xf0 and tag
     of 0x90:
@@ -422,7 +424,15 @@ proc toPreserve*(n: SomeInteger): Preserve[void] =
   Preserve[void](kind: pkSignedInteger, int: n.BiggestInt)
 
 proc toPreserve*(n: BigInt): Preserve[void] =
-  Preserve[void](kind: pkBigInteger, bigint: n)
+  if initBigInt(low(BiggestInt)) < n and n < initBigInt(high(BiggestInt)):
+    var tmp: BiggestUint
+    for limb in n.limbs:
+      tmp = (tmp shl 32) or limb
+    if Negative in n.flags:
+      tmp = (not tmp) + 1
+    result = Preserve[void](kind: pkSignedInteger, int: cast[BiggestInt](tmp))
+  else:
+    result = Preserve[void](kind: pkBigInteger, bigint: n)
 
 proc toPreserve*(s: string): Preserve[void] =
   Preserve[void](kind: pkString, string: s)
diff --git a/tests/test_integers.nim b/tests/test_integers.nim
index 93ed728..0950a1b 100644
--- a/tests/test_integers.nim
+++ b/tests/test_integers.nim
@@ -50,8 +50,8 @@ suite "native":
 
 suite "big":
   let testVectors = @[
-  ("87112285931760246646623899502532662132736", "B012010000000000000000000000000000000000"),
-  ("-87112285931760246646623899502532662132736", "B012FF0000000000000000000000000000000000"),
+  ("87112285931760246646623899502532662132736",
+      "B012010000000000000000000000000000000000"),
   ]
 
   for (decimals, hex) in testVectors: