bpo-45061: Revert unicode_is_singleton() change (GH-28516)

vstinner · web-flow · commit 8620be99da93 · 2021-09-22T12:16:53.000+02:00
Don't use a loop over 256 items, only checks for a single singleton.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
@@ -1994,8 +1994,10 @@ unicode_is_singleton(PyObject *unicode)
     if (unicode == state->empty_string) {
         return 1;
     }
-    for (Py_ssize_t i = 0; i < 256; i++) {
-        if (unicode == state->latin1[i]) {
+    PyASCIIObject *ascii = (PyASCIIObject *)unicode;
+    if (ascii->state.kind != PyUnicode_WCHAR_KIND && ascii->length == 1) {
+        Py_UCS4 ch = PyUnicode_READ_CHAR(unicode, 0);
+        if (ch < 256 && state->latin1[ch] == unicode) {
             return 1;
         }
     }

Original file line number	Diff line number	Diff line change
`@@ -1994,8 +1994,10 @@ unicode_is_singleton(PyObject *unicode)`
`1994`	`1994`	`if (unicode == state->empty_string) {`
`1995`	`1995`	`return 1;`
`1996`	`1996`	`}`
`1997`		`- for (Py_ssize_t i = 0; i < 256; i++) {`
`1998`		`- if (unicode == state->latin1[i]) {`
	`1997`	`+ PyASCIIObject ascii = (PyASCIIObject )unicode;`
	`1998`	`+ if (ascii->state.kind != PyUnicode_WCHAR_KIND && ascii->length == 1) {`
	`1999`	`+ Py_UCS4 ch = PyUnicode_READ_CHAR(unicode, 0);`
	`2000`	`+ if (ch < 256 && state->latin1[ch] == unicode) {`
`1999`	`2001`	`return 1;`
`2000`	`2002`	`}`
`2001`	`2003`	`}`