From 5be5e3b20e7cebcc99c4bc4ca3f4311496ecb4fb Mon Sep 17 00:00:00 2001
From: Alberto Restifo <alberto@restifo.dev>
Date: Fri, 24 Apr 2020 11:57:12 +0200
Subject: [PATCH] Add support for big numbers

---
 spec/rfc_spec.cr       |  6 +++---
 src/cbor.cr            |  2 ++
 src/cbor/diagnostic.cr | 23 ++++++++++++++++++++++-
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/spec/rfc_spec.cr b/spec/rfc_spec.cr
index 2ffe10f..534ed90 100644
--- a/spec/rfc_spec.cr
+++ b/spec/rfc_spec.cr
@@ -27,9 +27,9 @@ tests = [
   { %(1000000), "1a 00 0f 42 40" },
   { %(1000000000000), "1b 00 00 00 e8 d4 a5 10 00" },
   { %(18446744073709551615), "1b ff ff ff ff ff ff ff ff" },
-  # { %(18446744073709551616), "c2 49 01 00 00 00 00 00 00 00 00" },
+  { %(18446744073709551616), "c2 49 01 00 00 00 00 00 00 00 00" },
   { %(-18446744073709551616), "3b ff ff ff ff ff ff ff ff" },
-  # { %(-18446744073709551617), "c3 49 01 00 00 00 00 00 00 00 00" },
+  { %(-18446744073709551617), "c3 49 01 00 00 00 00 00 00 00 00" },
   { %(-1), "20" },
   { %(-10), "29" },
   { %(-100), "38 63" },
@@ -54,7 +54,7 @@ tests = [
   { %(simple(255)), "f8 ff" },
   { %(0("2013-03-21T20:04:00Z")), "c0 74 32 30 31 33 2d 30 33 2d 32 31 54 32 30 3a 30 34 3a 30 30 5a" },
   { %(1(1363896240)), "c1 1a 51 4b 67 b0" },
-  # { %(1(1363896240.5)), "c1 fb 41 d4 52 d9 ec 20 00 00" },
+  { %(1(1363896240.5)), "c1 fb 41 d4 52 d9 ec 20 00 00" },
   { %(23(h'01020304')), "d7 44 01 02 03 04" },
   { %(24(h'6449455446')), "d8 18 45 64 49 45 54 46" },
   { %(32("http://www.example.com")), "d8 20 76 68 74 74 70 3a 2f 2f 77 77 77 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d" },
diff --git a/src/cbor.cr b/src/cbor.cr
index 8418855..a1312c9 100644
--- a/src/cbor.cr
+++ b/src/cbor.cr
@@ -1,3 +1,5 @@
+require "big"
+
 require "./cbor/**"
 
 # TODO: Write documentation for `CBOR`
diff --git a/src/cbor/diagnostic.cr b/src/cbor/diagnostic.cr
index da06286..6d58652 100644
--- a/src/cbor/diagnostic.cr
+++ b/src/cbor/diagnostic.cr
@@ -53,7 +53,14 @@ class CBOR::Diagnostic
     when Token::SimpleValueT
       token.value.to_diagnostic
     when Token::TagT
-      "#{token.value.value.to_s}(#{next_value})"
+      case token.value
+      when Tag::PositiveBigNum
+        read_big_int
+      when Tag::NegativeBigNum
+        read_big_int(negative: true)
+      else
+        "#{token.value.value.to_s}(#{next_value})"
+      end
     when Token::FloatT
       return "NaN" if token.value.nan?
       return token.value.to_s if token.value.finite?
@@ -103,6 +110,20 @@ class CBOR::Diagnostic
     key_pairs
   end
 
+  private def read_big_int(negative : Bool = false) : String
+    token = @lexer.next_token
+    raise ParseError.new("Unexpected EOF after tag") unless token
+    raise ParseError.new("Unexpected type #{token.class}, want Token::BytesT") unless token.is_a?(Token::BytesT)
+
+    big = BigInt.new(token.value.hexstring, 16)
+    if negative
+      big *= -1
+      big -= 1
+    end
+
+    big.to_s
+  end
+
   private def key_value(key : Token::T, value : Token::T) : String
     "#{to_diagnostic(key)}: #{to_diagnostic(value)}"
   end