Fix fractional unix timestamps handling

spec/cbor/from_cbor_spec.cr

@@ -16,13 +16,13 @@ describe "CBOR helpers on basic types" do
        Bytes[0xc0, 0x74, 0x32, 0x30, 0x31, 0x33, 0x2d, 0x30, 0x33, 0x2d, 0x32, 0x31, 0x54, 0x32, 0x30, 0x3a, 0x30, 0x34, 0x3a, 0x30, 0x30, 0x5a],
        Time::Format::RFC_3339.parse("2013-03-21T20:04:00Z")},
       {Time, Bytes[0xc1, 0x1a, 0x51, 0x4b, 0x67, 0xb0], Time.unix(1363896240)},
-      {Time, Bytes[0xc1, 0xfb, 0x41, 0xd4, 0x52, 0xd9, 0xec, 0x20, 0x00, 0x00], Time.unix_ms((1363896240.5 * 1000).to_i)},
+      {Time, Bytes[0xc1, 0xfb, 0x41, 0xd4, 0x52, 0xd9, 0xec, 0x20, 0x00, 0x00], Time.unix_ms((BigFloat.new(1363896240.5) * 1000).to_u64)},
     ]
 
     tests.each do |tt|
       type, bytes, want = tt
 
-      it "decodes #{type.class}" do
+      it "decodes #{type}" do
         res = type.from_cbor(bytes)
         res.should eq(want)
       end

src/cbor/decoder.cr

@@ -42,7 +42,7 @@ class CBOR::Decoder
   end
 
   def read_tag : Tag
-    read_type(Token::TagT) { |token| token.value }
+    read_type(Token::TagT, ignore_tag: false) { |token| token.value }
   end
 
   def read_bool : Bool
@@ -64,7 +64,7 @@ class CBOR::Decoder
 
   private macro read_type(type, finish_token = true, ignore_tag = true, &block)
     # Skip the tag unless the token we want to read is a tag
-    {% if type != Token::TagT && ignore_tag %}
+    {% if ignore_tag %}
       if @current_token.is_a?(Token::TagT)
         finish_token!
       end

src/cbor/from_cbor.cr

@@ -40,7 +40,7 @@ def Time.new(decoder : CBOR::Decoder)
     when Int
       Time.unix(num)
     when Float
-      Time.unix_ms((num * 1000).to_i)
+      Time.unix_ms((BigFloat.new(num) * 1_000).to_u64)
     end
   else
     raise CBOR::ParseError.new("Expected tag to have value 0 or 1, got #{tag.value.to_s}")