gh-123497: New limit for Python integers on 64-bit platforms

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 64-bit integer.

Both limits are much larger than what can be available on practice, so
there is no effect on users.

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

Author: serhiy-storchaka

Include/cpython/longobject.h

@@ -71,8 +71,7 @@ PyAPI_FUNC(int) _PyLong_Sign(PyObject *v);
    absolute value of a long.  For example, this returns 1 for 1 and -1, 2
    for 2 and -2, and 2 for 3 and -3.  It returns 0 for 0.
    v must not be NULL, and must be a normalized long.
-   (uint64_t)-1 is returned and OverflowError set if the true result doesn't
-   fit in a size_t.
+   Always successful.
 */
 PyAPI_FUNC(uint64_t) _PyLong_NumBits(PyObject *v);
 

Include/internal/pycore_long.h

@@ -79,14 +79,13 @@ static inline PyObject* _PyLong_FromUnsignedChar(unsigned char i)
 }
 
 // _PyLong_Frexp returns a double x and an exponent e such that the
-// true value is approximately equal to x * 2**e.  e is >= 0.  x is
+// true value is approximately equal to x * 2**e.  x is
 // 0.0 if and only if the input is 0 (in which case, e and x are both
-// zeroes); otherwise, 0.5 <= abs(x) < 1.0.  On overflow, which is
-// possible if the number of bits doesn't fit into a Py_ssize_t, sets
-// OverflowError and returns -1.0 for x, 0 for e.
+// zeroes); otherwise, 0.5 <= abs(x) < 1.0.
+// Always successful.
 //
 // Export for 'math' shared extension
-PyAPI_DATA(double) _PyLong_Frexp(PyLongObject *a, int64_t *e);
+PyAPI_DATA(double) _PyLong_Frexp(PyLongObject *a, uint64_t *e);
 
 extern PyObject* _PyLong_FromBytes(const char *, Py_ssize_t, int);
 

Modules/_pickle.c

@@ -2155,8 +2155,7 @@ save_long(PicklerObject *self, PyObject *obj)
             return 0;
         }
         nbits = _PyLong_NumBits(obj);
-        if (nbits == (uint64_t)-1 && PyErr_Occurred())
-            goto error;
+        assert(!PyErr_Occurred());
         /* How many bytes do we need?  There are nbits >> 3 full
          * bytes of data, and nbits & 7 leftover bits.  If there
          * are any leftover bits, then we clearly need another

Modules/_randommodule.c

@@ -335,8 +335,7 @@ random_seed(RandomObject *self, PyObject *arg)
 
     /* Now split n into 32-bit chunks, from the right. */
     bits = _PyLong_NumBits(n);
-    if (bits == (uint64_t)-1 && PyErr_Occurred())
-        goto Done;
+    assert(!PyErr_Occurred());
 
     /* Figure out how many 32-bit chunks this gives us. */
     keyused = bits == 0 ? 1 : (size_t)((bits - 1) / 32 + 1);

Modules/mathmodule.c

@@ -1680,9 +1680,7 @@ math_isqrt(PyObject *module, PyObject *n)
 
     /* c = (n.bit_length() - 1) // 2 */
     c = _PyLong_NumBits(n);
-    if (c == (uint64_t)(-1)) {
-        goto error;
-    }
+    assert(!PyErr_Occurred());
     c = (c - 1U) / 2U;
 
     /* Fast path: if c <= 31 then n < 2**64 and we can compute directly with a
@@ -2185,7 +2183,7 @@ loghelper(PyObject* arg, double (*func)(double))
     /* If it is int, do it ourselves. */
     if (PyLong_Check(arg)) {
         double x, result;
-        int64_t e;
+        uint64_t e;
 
         /* Negative or zero inputs give a ValueError. */
         if (!_PyLong_IsPositive((PyLongObject *)arg)) {
@@ -2202,8 +2200,7 @@ loghelper(PyObject* arg, double (*func)(double))
                to compute the log anyway.  Clear the exception and continue. */
             PyErr_Clear();
             x = _PyLong_Frexp((PyLongObject *)arg, &e);
-            if (x == -1.0 && PyErr_Occurred())
-                return NULL;
+            assert(!PyErr_Occurred());
             /* Value is ~= x * 2**e, so the log ~= log(x) + log(2) * e. */
             result = func(x) + func(2.0) * e;
         }

Objects/floatobject.c

@@ -419,11 +419,7 @@ float_richcompare(PyObject *v, PyObject *w, int op)
              * its magnitude must exceed the magnitude of any
              * finite float.
              */
-            if (nbits64 == (uint64_t)-1 && PyErr_Occurred()) {
-                /* This Python integer is so large that uint64_t isn't
-                 * big enough to hold the # of bits. */
-                PyErr_Clear();
-            }
+            assert(!PyErr_Occurred());
             i = (double)vsign;
             assert(wsign != 0);
             j = wsign * 2.0;