Issue #14744: Use the new _PyUnicodeWriter internal API to speed up str%args and str.format(args)

 * Formatting string, int, float and complex use the _PyUnicodeWriter API. It
   avoids a temporary buffer in most cases.
 * Add _PyUnicodeWriter_WriteStr() to restore the PyAccu optimization: just
   keep a reference to the string if the output is only composed of one string
 * Disable overallocation when formatting the last argument of str%args and
   str.format(args)
 * Overallocation allocates at least 100 characters: add min_length attribute
   to the _PyUnicodeWriter structure
 * Add new private functions: _PyUnicode_FastCopyCharacters(),
   _PyUnicode_FastFill() and _PyUnicode_FromASCII()

The speed up is around 20% in average.

1 files changed, 13 insertions, 5 deletions

diff --git a/Include/longobject.h b/Include/longobject.h
index c58ddf4400..d741f1b4c0 100644
--- a/Include/longobject.h
+++ b/Include/longobject.h
@@ -151,14 +151,22 @@ PyAPI_FUNC(int) _PyLong_AsByteArray(PyLongObject* v,
 
 /* _PyLong_Format: Convert the long to a string object with given base,
    appending a base prefix of 0[box] if base is 2, 8 or 16. */
-PyAPI_FUNC(PyObject *) _PyLong_Format(PyObject *aa, int base);
+PyAPI_FUNC(PyObject *) _PyLong_Format(PyObject *obj, int base);
+
+PyAPI_FUNC(int) _PyLong_FormatWriter(
+    _PyUnicodeWriter *writer,
+    PyObject *obj,
+    int base,
+    int alternate);
 
 /* Format the object based on the format_spec, as defined in PEP 3101
    (Advanced String Formatting). */
-PyAPI_FUNC(PyObject *) _PyLong_FormatAdvanced(PyObject *obj,
-                                              PyObject *format_spec,
-                                              Py_ssize_t start,
-                                              Py_ssize_t end);
+PyAPI_FUNC(int) _PyLong_FormatAdvancedWriter(
+    _PyUnicodeWriter *writer,
+    PyObject *obj,
+    PyObject *format_spec,
+    Py_ssize_t start,
+    Py_ssize_t end);
 #endif /* Py_LIMITED_API */
 
 /* These aren't really part of the long object, but they're handy. The