gh-73939: Fix bitfiled not matching C on mac/linux.

Lib/test/test_ctypes/test_structures.py

@@ -738,6 +738,30 @@ class Test8(Union):
  self.assertEqual(ctx.exception.args[0], 'item 1 in _argtypes_ passes '
  'a union by value, which is unsupported.')
 
+ def test_bitfield_matches_c(self):
+ class Test9(Structure):
+ _pack_ = 1
+ _fields_ = (('A', c_uint16), # 2 bytes
+ ('B', c_uint16, 9),
+ ('C', c_uint16, 1),
+ ('D', c_uint16, 1),
+ ('E', c_uint16, 1),
+ ('F', c_uint16, 1),
+ ('G', c_uint16, 3), # 4 bytes
+ ('H', c_uint32, 10),
+ ('I', c_uint32, 20),
+ ('J', c_uint32, 2)) # 8 bytes
+ dll = CDLL(_ctypes_test.__file__)
+ func = dll._testfunc_bitfield_by_reference3
+ func.restype = c_long
+ func.argtypes = (POINTER(Test9),c_long,)
+ ind = 0
+ for field in Test9._fields_:
+ test9 = Test9()
+ setattr(test9,field[0], 1)
+ self.assertEqual(func(test9, ind), 1)
+ ind += 1
+
 class PointerMemberTestCase(unittest.TestCase):
 
  def test(self):

Modules/_ctypes/_ctypes_test.c

@@ -231,6 +231,31 @@ _testfunc_bitfield_by_reference2(Test7 *in) {
  return result;
 }
 
+typedef struct{
+ uint16_t A ;
+ uint16_t B : 9;
+ uint16_t C : 1;
+ uint16_t D : 1;
+ uint16_t E : 1;
+ uint16_t F : 1;
+ uint16_t G : 3;
+ uint32_t H : 10;
+ uint32_t I : 20;
+ uint32_t J : 2;
+} Test9;
+
+EXPORT(long)
+_testfunc_bitfield_by_reference3(Test9 *in, long pos) {
+ long data[] = {in->A , in->B , in->C , in->D , in->E , in->F , in->G , in->H , in->I , in->J};
+ long data_length = (long) (sizeof(data)/sizeof(data[0]));
+ if(pos < 0)
+ return -1;
+ if(pos >= data_length)
+ return -1;
+
+ return data[pos];
+}
+
 typedef union {
  signed int A: 1, B:2, C:3, D:2;
 } Test8;

Modules/_ctypes/cfield.c

@@ -86,6 +86,7 @@ PyCField_FromDesc(PyObject *desc, Py_ssize_t index,
 #ifndef MS_WIN32
  } else if (bitsize /* this is a bitfield request */
  && *pfield_size /* we have a bitfield open */
+ && *pfield_size != *pbitofs /* Current field has been filled, start new one */
  && dict->size * 8 >= *pfield_size
  && (*pbitofs + bitsize) <= dict->size * 8) {
  /* expand bit field */