Optimize ascii/latin1+surrogateescape encoders

Issue #25227: Optimize ASCII and latin1 encoders with the ``surrogateescape``
error handler: the encoders are now up to 3 times as fast.

Initial patch written by Serhiy Storchaka.

Doc/whatsnew/3.6.rst

@@ -117,6 +117,9 @@ Optimizations
 * The ASCII decoder is now up to 60 times as fast for error handlers:
   ``surrogateescape``, ``ignore`` and ``replace``.
 
+* The ASCII and the Latin1 encoders are now up to 3 times as fast for the error
+  error ``surrogateescape``.
+
 
 Build and C API Changes
 =======================

Lib/test/test_codecs.py

@@ -3060,7 +3060,31 @@ class CodePageTest(unittest.TestCase):
 
 
 class ASCIITest(unittest.TestCase):
+    def test_encode(self):
+        self.assertEqual('abc123'.encode('ascii'), b'abc123')
+
+    def test_encode_error(self):
+        for data, error_handler, expected in (
+            ('[\x80\xff\u20ac]', 'ignore', b'[]'),
+            ('[\x80\xff\u20ac]', 'replace', b'[???]'),
+            ('[\x80\xff\u20ac]', 'xmlcharrefreplace', b'[€ÿ€]'),
+            ('[\x80\xff\u20ac]', 'backslashreplace', b'[\\x80\\xff\\u20ac]'),
+            ('[\udc80\udcff]', 'surrogateescape', b'[\x80\xff]'),
+        ):
+            with self.subTest(data=data, error_handler=error_handler,
+                              expected=expected):
+                self.assertEqual(data.encode('ascii', error_handler),
+                                 expected)
+
+    def test_encode_surrogateescape_error(self):
+        with self.assertRaises(UnicodeEncodeError):
+            # the first character can be decoded, but not the second
+            '\udc80\xff'.encode('ascii', 'surrogateescape')
+
     def test_decode(self):
+        self.assertEqual(b'abc'.decode('ascii'), 'abc')
+
+    def test_decode_error(self):
         for data, error_handler, expected in (
             (b'[\x80\xff]', 'ignore', '[]'),
             (b'[\x80\xff]', 'replace', '[\ufffd\ufffd]'),
@@ -3073,5 +3097,41 @@ class ASCIITest(unittest.TestCase):
                                  expected)
 
 
+class Latin1Test(unittest.TestCase):
+    def test_encode(self):
+        for data, expected in (
+            ('abc', b'abc'),
+            ('\x80\xe9\xff', b'\x80\xe9\xff'),
+        ):
+            with self.subTest(data=data, expected=expected):
+                self.assertEqual(data.encode('latin1'), expected)
+
+    def test_encode_errors(self):
+        for data, error_handler, expected in (
+            ('[\u20ac\udc80]', 'ignore', b'[]'),
+            ('[\u20ac\udc80]', 'replace', b'[??]'),
+            ('[\u20ac\udc80]', 'backslashreplace', b'[\\u20ac\\udc80]'),
+            ('[\u20ac\udc80]', 'xmlcharrefreplace', b'[€�]'),
+            ('[\udc80\udcff]', 'surrogateescape', b'[\x80\xff]'),
+        ):
+            with self.subTest(data=data, error_handler=error_handler,
+                              expected=expected):
+                self.assertEqual(data.encode('latin1', error_handler),
+                                 expected)
+
+    def test_encode_surrogateescape_error(self):
+        with self.assertRaises(UnicodeEncodeError):
+            # the first character can be decoded, but not the second
+            '\udc80\u20ac'.encode('latin1', 'surrogateescape')
+
+    def test_decode(self):
+        for data, expected in (
+            (b'abc', 'abc'),
+            (b'[\x80\xff]', '[\x80\xff]'),
+        ):
+            with self.subTest(data=data, expected=expected):
+                self.assertEqual(data.decode('latin1'), expected)
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS

@@ -10,6 +10,10 @@ Release date: XXXX-XX-XX
 Core and Builtins
 -----------------
 
+- Issue #25227: Optimize ASCII and latin1 encoders with the ``surrogateescape``
+  error handler: the encoders are now up to 3 times as fast. Initial patch
+  written by Serhiy Storchaka.
+
 - Issue #25003: On Solaris 11.3 or newer, os.urandom() now uses the
   getrandom() function instead of the getentropy() function. The getentropy()
   function is blocking to generate very good quality entropy, os.urandom()

Objects/unicodeobject.c

@@ -6532,6 +6532,22 @@ unicode_encode_ucs1(PyObject *unicode,
                 pos = collend;
                 break;
 
+            case _Py_ERROR_SURROGATEESCAPE:
+                for (i = collstart; i < collend; ++i) {
+                    ch = PyUnicode_READ(kind, data, i);
+                    if (ch < 0xdc80 || 0xdcff < ch) {
+                        /* Not a UTF-8b surrogate */
+                        break;
+                    }
+                    *str++ = (char)(ch - 0xdc00);
+                    ++pos;
+                }
+                if (i >= collend)
+                    break;
+                collstart = pos;
+                assert(collstart != collend);
+                /* fallback to general error handling */
+
             default:
                 repunicode = unicode_encode_call_errorhandler(errors, &error_handler_obj,
                                                               encoding, reason, unicode, &exc,