Fix bug in compact sequence constructor

rdata/parser/_parser.py

@@ -451,16 +451,21 @@ def compact_seq_constructor(
         reference=0,
     )
 
+    n = int(state.value[0])
     start = state.value[1]
-    stop = state.value[0]
     step = state.value[2]
 
     if is_int:
         start = int(start)
-        stop = int(stop)
         step = int(step)
-
-    value = np.arange(start, stop, step)
+        # Calculate stop with integer arithmetic
+        # and use built-in range() for numerical stability
+        stop = start + (n - 1) * step
+        value = np.array(range(start, stop + 1, step))
+    else:
+        # Calculate stop with floating-point arithmetic
+        stop = start + (n - 1) * step
+        value = np.linspace(start, stop, n)
 
     return new_info, value
 

rdata/tests/test_rdata.py

@@ -632,6 +632,22 @@ def test_altrep_compact_intseq(self) -> None:
             "test_altrep_compact_intseq": np.arange(1000),
         })
 
+    def test_altrep_compact_intseq_asymmetric(self) -> None:
+        """
+        Test alternative representation of sequences of ints.
+
+        This test an origin different from 0, to reproduce
+        issue #29.
+        """
+        parsed = rdata.parser.parse_file(
+            TESTDATA_PATH / "test_altrep_compact_intseq_asymmetric.rda",
+        )
+        converted = rdata.conversion.convert(parsed)
+
+        np.testing.assert_equal(converted, {
+            "test_altrep_compact_intseq_asymmetric": np.arange(-5, 6),
+        })
+
     def test_altrep_compact_realseq(self) -> None:
         """Test alternative representation of sequences of ints."""
         parsed = rdata.parser.parse_file(
@@ -643,6 +659,22 @@ def test_altrep_compact_realseq(self) -> None:
             "test_altrep_compact_realseq": np.arange(1000.0),
         })
 
+    def test_altrep_compact_realseq_asymmetric(self) -> None:
+        """
+        Test alternative representation of sequences of ints.
+
+        This test an origin different from 0, to reproduce
+        issue #29.
+        """
+        parsed = rdata.parser.parse_file(
+            TESTDATA_PATH / "test_altrep_compact_realseq_asymmetric.rda",
+        )
+        converted = rdata.conversion.convert(parsed)
+
+        np.testing.assert_equal(converted, {
+            "test_altrep_compact_realseq_asymmetric": np.arange(-5.0, 6.0),
+        })
+
     def test_altrep_deferred_string(self) -> None:
         """Test alternative representation of deferred strings."""
         parsed = rdata.parser.parse_file(