fixing subnormal cross-platform

Author: SwayamInSync

quaddtype/numpy_quaddtype/src/quaddtype_main.c

@@ -71,7 +71,26 @@ get_sleef_constant(PyObject *self, PyObject *args)
         result->value.sleef_value = SLEEF_QUAD_MIN;
     }
     else if (strcmp(constant_name, "smallest_subnormal") == 0) {
+#ifdef SLEEF_QUAD_C
+        // On platforms with native __float128 support, use the correct literal
         result->value.sleef_value = SLEEF_QUAD_DENORM_MIN;
+#else
+        // On platforms without native __float128, SLEEF_QUAD_DENORM_MIN is broken
+        // Manually constructing the smallest subnormal: 1 * 2^(-16382-112) = 2^(-16494)
+        // This represents 0x0.0000000000000000000000000001p-16382
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
+        struct {
+            uint64_t h, l;
+        } c;
+#else
+        struct {
+            uint64_t l, h;
+        } c;
+#endif
+        c.h = 0x0000000000000000ULL;  // exponent = 0 (subnormal), mantissa high = 0
+        c.l = 0x0000000000000001ULL;  // mantissa low = 1 (smallest possible)
+        memcpy(&result->value.sleef_value, &c, 16);
+#endif
     }
     else if (strcmp(constant_name, "bits") == 0) {
         Py_DECREF(result);

quaddtype/tests/test_quaddtype.py

@@ -24,6 +24,16 @@ def test_finfo_constant(name):
     assert isinstance(getattr(numpy_quaddtype, name), QuadPrecision)
 
 
+def test_smallest_subnormal_value():
+    """Test that smallest_subnormal has the correct value across all platforms."""
+    smallest_sub = numpy_quaddtype.smallest_subnormal
+    repr_str = repr(smallest_sub)
+    
+    # The repr should show QuadPrecision('6.0e-4966', backend='sleef')
+    assert "6.0e-4966" in repr_str, f"Expected '6.0e-4966' in repr, got {repr_str}"
+    
+    assert smallest_sub > 0, "smallest_subnormal should be positive"
+
 @pytest.mark.parametrize("name,value", [("bits", 128), ("precision", 33)])
 def test_finfo_int_constant(name, value):
     assert getattr(numpy_quaddtype, name) == value