Try to use PyLong_As/FromNativeBytes API for mpz <-> int conversion

gmp.c

@@ -180,49 +180,12 @@ MPZ_from_str(PyObject *obj, int base)
     return res;
 }
 
+static zz_err zz_set_bytes(const unsigned char *buffer, size_t length,
+                           bool is_signed, zz_t *u);
+
 static MPZ_Object *
 MPZ_from_int(PyObject *obj)
 {
-#if defined(ON_CPYTHON) && !defined(Py_LIMITED_API)
-    PyLongExport long_export = {0, 0, 0, 0, 0};
-    const zz_layout *int_layout = (zz_layout *)PyLong_GetNativeLayout();
-    MPZ_Object *res = NULL;
-
-    if (PyLong_Export(obj, &long_export) < 0) {
-        return res; /* LCOV_EXCL_LINE */
-    }
-    if (long_export.digits) {
-        res = MPZ_new();
-        if (!res) {
-            return NULL; /* LCOV_EXCL_LINE */
-        }
-
-        zz_err ret = zz_import((size_t)long_export.ndigits,
-                               long_export.digits, *int_layout, &res->z);
-
-        if (ret) {
-            /* LCOV_EXCL_START */
-            if (ret == ZZ_MEM) {
-                return (MPZ_Object *)PyErr_NoMemory();
-            }
-            PyErr_SetString(PyExc_OverflowError,
-                            "too many digits in integer");
-            return NULL;
-            /* LCOV_EXCL_STOP */
-        }
-        if (long_export.negative) {
-            (void)zz_neg(&res->z, &res->z);
-        }
-        PyLong_FreeExport(&long_export);
-    }
-    else {
-        res = MPZ_new();
-        if (res && zz_set(long_export.value, &res->z)) {
-            PyErr_NoMemory(); /* LCOV_EXCL_LINE */
-        }
-    }
-    return res;
-#else
     int64_t value;
 
     if (!PyLong_AsInt64(obj, &value)) {
@@ -235,6 +198,50 @@ MPZ_from_int(PyObject *obj)
     }
     PyErr_Clear();
 
+#if defined(ON_CPYTHON) && PY_VERSION_HEX > 0x030D00A0 \
+        && !defined(Py_LIMITED_API)
+    Py_ssize_t expected = PyLong_AsNativeBytes(obj, NULL, 0, 0);
+
+    if (expected < 0) {
+        return NULL; /* LCOV_EXCL_LINE */
+    }
+
+    unsigned char *buffer = malloc((size_t)expected);
+
+    if (!buffer) {
+        return (MPZ_Object *)PyErr_NoMemory(); /* LCOV_EXCL_LINE */
+    }
+
+    expected = PyLong_AsNativeBytes(obj, buffer, expected, 0);
+    if (expected < 0) {
+free:
+        /* LCOV_EXCL_START */
+        free(buffer);
+        return NULL;
+        /* LCOV_EXCL_STOP */
+    }
+
+    MPZ_Object *res = MPZ_new();
+
+    if (!res) {
+        goto free; /* LCOV_EXCL_LINE */
+    }
+
+    zz_err ret = zz_set_bytes(buffer, (size_t)expected, true, &res->z);
+
+    free(buffer);
+    if (ret) {
+        /* LCOV_EXCL_START */
+        if (ret == ZZ_MEM) {
+            return (MPZ_Object *)PyErr_NoMemory();
+        }
+        PyErr_SetString(PyExc_OverflowError,
+                        "too many digits in integer");
+        return NULL;
+        /* LCOV_EXCL_STOP */
+    }
+    return res;
+#else
     PyObject *str = PyNumber_ToBase(obj, 16);
 
     if (!str) {
@@ -245,9 +252,14 @@ MPZ_from_int(PyObject *obj)
 
     Py_DECREF(str);
     return res;
-#endif /* defined(ON_CPYTHON) && !defined(Py_LIMITED_API) */
+#endif /* defined(ON_CPYTHON) && PY_VERSION_HEX > 0x030D00A0
+          && !defined(Py_LIMITED_API) */
 }
 
+static zz_err zz_get_bytes(const zz_t *u, size_t length,
+                           bool is_signed, unsigned char **buffer);
+static void revstr(unsigned char *s, Py_ssize_t l, Py_ssize_t r);
+
 static PyObject *
 MPZ_to_int(MPZ_Object *u)
 {
@@ -257,19 +269,21 @@ MPZ_to_int(MPZ_Object *u)
         return PyLong_FromInt64(value);
     }
 
-#if defined(ON_CPYTHON) && !defined(Py_LIMITED_API)
-    const zz_layout *int_layout = (zz_layout *)PyLong_GetNativeLayout();
-    size_t size = (zz_bitlen(&u->z) + int_layout->bits_per_digit
-                   - 1)/int_layout->bits_per_digit;
-    void *digits;
-    PyLongWriter *writer = PyLongWriter_Create(zz_isneg(&u->z),
-                                               (Py_ssize_t)size, &digits);
+#if defined(ON_CPYTHON) && PY_VERSION_HEX > 0x030D00A0 \
+        && !defined(Py_LIMITED_API)
+    size_t size = (zz_bitlen(&u->z) + 7)/8 + 1;
+    unsigned char *buffer = malloc(size);
 
-    if (!writer) {
-        return NULL; /* LCOV_EXCL_LINE */
+    if (!buffer) {
+        return PyErr_NoMemory(); /* LCOV_EXCL_LINE */
     }
-    (void)zz_export(&u->z, *int_layout, size, digits);
-    return PyLongWriter_Finish(writer);
+    (void)zz_get_bytes(&u->z, size, true, &buffer);
+    revstr(buffer, 0, (Py_ssize_t)size - 1);
+
+    PyObject *res = PyLong_FromNativeBytes(buffer, size, -1);
+
+    free(buffer);
+    return res;
 #else
     size_t len;
 
@@ -289,7 +303,8 @@ MPZ_to_int(MPZ_Object *u)
 
     free(buf);
     return res;
-#endif /* defined(ON_CPYTHON) && !defined(Py_LIMITED_API) */
+#endif /* defined(ON_CPYTHON) && PY_VERSION_HEX > 0x030D00A0
+          && !defined(Py_LIMITED_API) */
 }
 
 static void