dfilter: Allow existence check for slices

Allow checking if a slice exists. The result is true if the
slice has length greater than zero.

The len() function is implemented as a DFVM instruction instead.
The semantics are the same.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/suite_dfilter/group_range_method.py b/test/suite_dfilter/group_slice.py
index 143b223cd0..4aa686c57c 100644
--- a/test/suite_dfilter/group_range_method.py
+++ b/test/suite_dfilter/group_slice.py
@@ -78,3 +78,19 @@ class case_range(unittest.TestCase):
     def test_slice_range_5(self, checkDFilterSucceed):
         dfilter = "frame[20:] contains :12345678"
         checkDFilterSucceed(dfilter)
+
+    def test_slice_exists_1(self, checkDFilterCount):
+        dfilter = "frame[59]"
+        checkDFilterCount(dfilter, 1)
+
+    def test_slice_exists_2(self, checkDFilterCount):
+        dfilter = "frame[60]"
+        checkDFilterCount(dfilter, 0)
+
+    def test_slice_exists_3(self, checkDFilterCount):
+        dfilter = "frame[50-59]"
+        checkDFilterCount(dfilter, 1)
+
+    def test_slice_exists_4(self, checkDFilterCount):
+        dfilter = "frame[50-60]"
+        checkDFilterCount(dfilter, 0)