Fix a bug spotted by Chris in my BigInteger patch; thanks!

The problem was this:
  Console.WriteLine(Int64.Parse("08000000000000000", NumberStyles.HexNumber));
  // => -9223372036854775808
  Console.WriteLine(Int64.Parse("9223372036854775808"));
  // => Value was either too large or too small for an Int64.

In other words, large hex numbers are interpreted as a sequence of bits, not as
an actual number.

3 files changed, 18 insertions, 2 deletions

diff --git a/Source/Dafny/BigIntegerParser.cs b/Source/Dafny/BigIntegerParser.cs
index 94e842cc..cd2cf314 100644
--- a/Source/Dafny/BigIntegerParser.cs
+++ b/Source/Dafny/BigIntegerParser.cs
@@ -11,8 +11,8 @@ namespace Microsoft.Dafny {
         ///   Int64, and only falling back if needed.
         /// </summary>
         internal static BigInteger Parse(string str, NumberStyles style) {
-            Int64 parsed;
-            if (Int64.TryParse(str, style, NumberFormatInfo.CurrentInfo, out parsed)) {
+            UInt64 parsed;
+            if (UInt64.TryParse(str, style, NumberFormatInfo.CurrentInfo, out parsed)) {
                 return new BigInteger(parsed);
             } else {
                 // Throws on Mono 3.2.8
diff --git a/Test/dafny4/LargeConstants.dfy b/Test/dafny4/LargeConstants.dfy
new file mode 100644
index 00000000..18435c30
--- /dev/null
+++ b/Test/dafny4/LargeConstants.dfy
@@ -0,0 +1,14 @@
+// RUN: %dafny /compile:0 /dprint:"%t.dprint" "%s" > "%t"

+// RUN: %diff "%s.expect" "%t"

+

+lemma largeIsLarge()

+  ensures 0x8000000000000000 > 0 {

+}

+

+lemma SmallIsSmall()

+  ensures -0x8000000000000000 < 0 {

+}

+

+lemma ShouldCancelOut()

+  ensures -0x8000000000000000 + 0x8000000000000000 == 0 {

+}

diff --git a/Test/dafny4/LargeConstants.dfy.expect b/Test/dafny4/LargeConstants.dfy.expect
new file mode 100644
index 00000000..4ef2de53
--- /dev/null
+++ b/Test/dafny4/LargeConstants.dfy.expect
@@ -0,0 +1,2 @@
+

+Dafny program verifier finished with 6 verified, 0 errors