gh-123497: New limit for Python integers on 64-bit platforms (GH-123724)

Instead of be limited just by the size of addressable memory (2**63
bytes), Python integers are now also limited by the number of bits, so
the number of bit now always fit in a 64-bit integer.

Both limits are much larger than what might be available in practice,
so it doesn't affect users.

_PyLong_NumBits() and _PyLong_Frexp() are now always successful.

1 files changed, 12 insertions, 11 deletions

diff --git a/Python/ast_opt.c b/Python/ast_opt.c
index f5b0475..01e208b 100644
--- a/Python/ast_opt.c
+++ b/Python/ast_opt.c
@@ -169,11 +169,10 @@ safe_multiply(PyObject *v, PyObject *w)
     if (PyLong_Check(v) && PyLong_Check(w) &&
         !_PyLong_IsZero((PyLongObject *)v) && !_PyLong_IsZero((PyLongObject *)w)
     ) {
-        uint64_t vbits = _PyLong_NumBits(v);
-        uint64_t wbits = _PyLong_NumBits(w);
-        if (vbits == (uint64_t)-1 || wbits == (uint64_t)-1) {
-            return NULL;
-        }
+        int64_t vbits = _PyLong_NumBits(v);
+        int64_t wbits = _PyLong_NumBits(w);
+        assert(vbits >= 0);
+        assert(wbits >= 0);
         if (vbits + wbits > MAX_INT_SIZE) {
             return NULL;
         }
@@ -215,12 +214,13 @@ safe_power(PyObject *v, PyObject *w)
     if (PyLong_Check(v) && PyLong_Check(w) &&
         !_PyLong_IsZero((PyLongObject *)v) && _PyLong_IsPositive((PyLongObject *)w)
     ) {
-        uint64_t vbits = _PyLong_NumBits(v);
+        int64_t vbits = _PyLong_NumBits(v);
         size_t wbits = PyLong_AsSize_t(w);
-        if (vbits == (uint64_t)-1 || wbits == (size_t)-1) {
+        assert(vbits >= 0);
+        if (wbits == (size_t)-1) {
             return NULL;
         }
-        if (vbits > MAX_INT_SIZE / wbits) {
+        if ((uint64_t)vbits > MAX_INT_SIZE / wbits) {
             return NULL;
         }
     }
@@ -234,12 +234,13 @@ safe_lshift(PyObject *v, PyObject *w)
     if (PyLong_Check(v) && PyLong_Check(w) &&
         !_PyLong_IsZero((PyLongObject *)v) && !_PyLong_IsZero((PyLongObject *)w)
     ) {
-        uint64_t vbits = _PyLong_NumBits(v);
+        int64_t vbits = _PyLong_NumBits(v);
         size_t wbits = PyLong_AsSize_t(w);
-        if (vbits == (uint64_t)-1 || wbits == (size_t)-1) {
+        assert(vbits >= 0);
+        if (wbits == (size_t)-1) {
             return NULL;
         }
-        if (wbits > MAX_INT_SIZE || vbits > MAX_INT_SIZE - wbits) {
+        if (wbits > MAX_INT_SIZE || (uint64_t)vbits > MAX_INT_SIZE - wbits) {
             return NULL;
         }
     }