GH-101291: Rearrange the size bits in PyLongObject (GH-102464)

* Eliminate all remaining uses of Py_SIZE and Py_SET_SIZE on PyLongObject, adding asserts.

* Change layout of size/sign bits in longobject to support future addition of immortal ints and tagged medium ints.

* Add functions to hide some internals of long object, and for setting sign and digit count.

* Replace uses of IS_MEDIUM_VALUE macro with _PyLong_IsCompact().

1 files changed, 17 insertions, 9 deletions

diff --git a/Tools/gdb/libpython.py b/Tools/gdb/libpython.py
index 56d6970..e38bd59 100755
--- a/Tools/gdb/libpython.py
+++ b/Tools/gdb/libpython.py
@@ -882,10 +882,16 @@ class PyLongObjectPtr(PyObjectPtr):
     def proxyval(self, visited):
         '''
         Python's Include/longobjrep.h has this declaration:
-           struct _longobject {
-               PyObject_VAR_HEAD
-               digit ob_digit[1];
-           };
+
+            typedef struct _PyLongValue {
+                uintptr_t lv_tag; /* Number of digits, sign and flags */
+                digit ob_digit[1];
+            } _PyLongValue;
+
+            struct _longobject {
+                PyObject_HEAD
+               _PyLongValue long_value;
+            };
 
         with this description:
             The absolute value of a number is equal to
@@ -897,11 +903,13 @@ class PyLongObjectPtr(PyObjectPtr):
             #define PyLong_SHIFT        30
             #define PyLong_SHIFT        15
         '''
-        ob_size = int(self.field('ob_size'))
-        if ob_size == 0:
+        long_value = self.field('long_value')
+        lv_tag = int(long_value['lv_tag'])
+        size = lv_tag >> 3
+        if size == 0:
             return 0
 
-        ob_digit = self.field('long_value')['ob_digit']
+        ob_digit = long_value['ob_digit']
 
         if gdb.lookup_type('digit').sizeof == 2:
             SHIFT = 15
@@ -909,9 +917,9 @@ class PyLongObjectPtr(PyObjectPtr):
             SHIFT = 30
 
         digits = [int(ob_digit[i]) * 2**(SHIFT*i)
-                  for i in safe_range(abs(ob_size))]
+                  for i in safe_range(size)]
         result = sum(digits)
-        if ob_size < 0:
+        if (lv_tag & 3) == 2:
             result = -result
         return result