fixes #3985

compiler/semfold.nim

@@ -375,7 +375,12 @@ proc getAppType(n: PNode): PNode =
     result = newStrNodeT("console", n)
 
 proc rangeCheck(n: PNode, value: BiggestInt) =
-  if value < firstOrd(n.typ) or value > lastOrd(n.typ):
+  var err = false
+  if n.typ.skipTypes({tyRange}).kind in {tyUInt..tyUInt64}:
+    err = value <% firstOrd(n.typ) or value >% lastOrd(n.typ, fixedUnsigned=true)
+  else:
+    err = value < firstOrd(n.typ) or value > lastOrd(n.typ)
+  if err:
     localError(n.info, errGenerated, "cannot convert " & $value &
                                      " to " & typeToString(n.typ))
 

compiler/types.nim

@@ -621,7 +621,7 @@ proc firstOrd*(t: PType): BiggestInt =
     internalError("invalid kind for first(" & $t.kind & ')')
     result = 0
 
-proc lastOrd*(t: PType): BiggestInt =
+proc lastOrd*(t: PType; fixedUnsigned = false): BiggestInt =
   case t.kind
   of tyBool: result = 1
   of tyChar: result = 255
@@ -640,11 +640,14 @@ proc lastOrd*(t: PType): BiggestInt =
   of tyInt64: result = 0x7FFFFFFFFFFFFFFF'i64
   of tyUInt:
     if platform.intSize == 4: result = 0xFFFFFFFF
+    elif fixedUnsigned: result = 0xFFFFFFFFFFFFFFFF'i64
     else: result = 0x7FFFFFFFFFFFFFFF'i64
   of tyUInt8: result = 0xFF
   of tyUInt16: result = 0xFFFF
   of tyUInt32: result = 0xFFFFFFFF
-  of tyUInt64: result = 0x7FFFFFFFFFFFFFFF'i64
+  of tyUInt64:
+    if fixedUnsigned: result = 0xFFFFFFFFFFFFFFFF'i64
+    else: result = 0x7FFFFFFFFFFFFFFF'i64
   of tyEnum:
     assert(t.n.sons[sonsLen(t.n) - 1].kind == nkSym)
     result = t.n.sons[sonsLen(t.n) - 1].sym.position

tests/misc/tunsignedcmp.nim

@@ -9,6 +9,8 @@ true
 1
 0
 it should stop now
+18446744073709551615
+4294967295
 '''
 """
 
@@ -31,3 +33,11 @@ for i in countdown(count, 0):
   if i == 0:
     echo "it should stop now"
     stop_me = true
+
+# bug #3985
+const
+  HIGHEST_64BIT_UINT = 0xFFFFFFFFFFFFFFFF'u
+  HIGHEST_32BIT_UINT = 0xFFFFFFFF'u
+
+echo($HIGHEST_64BIT_UINT)
+echo($HIGHEST_32BIT_UINT)