Patch #416953: Cache ASCII characters to speed up ASCII decoding.

Objects/unicodeobject.c

@@ -90,6 +90,8 @@ static PyUnicodeObject *unicode_empty;
 static PyUnicodeObject *unicode_freelist;
 static int unicode_freelist_size;
 
+static PyUnicodeObject *unicode_ascii[128];
+
 /* Default encoding to use and assume when NULL is passed as encoding
    parameter; it is initialized by _PyUnicode_Init().
 
@@ -251,6 +253,19 @@ PyObject *PyUnicode_FromUnicode(const Py_UNICODE *u,
 {
     PyUnicodeObject *unicode;
 
+    if (size == 1 && *u < 128) {
+	    unicode = unicode_ascii[*u];
+	    if (!unicode) {
+		    unicode = _PyUnicode_New(1);
+		    unicode->str[0] = *u;
+		    if (!unicode)
+			    return NULL;
+		    unicode_ascii[*u] = unicode;
+	    }
+	    Py_INCREF(unicode);
+	    return (PyObject*)unicode;
+    }
+
     unicode = _PyUnicode_New(size);
     if (!unicode)
         return NULL;
@@ -1656,6 +1671,11 @@ PyObject *PyUnicode_DecodeASCII(const char *s,
     PyUnicodeObject *v;
     Py_UNICODE *p;
 
+    if (size == 1 && *(unsigned char*)s < 128) {
+	    Py_UNICODE r = *(unsigned char*)s;
+	    return PyUnicode_FromUnicode(&r, 1);
+    }
+    
     /* ASCII is equivalent to the first 128 ordinals in Unicode. */
     v = _PyUnicode_New(size);
     if (v == NULL)
@@ -5189,6 +5209,8 @@ PyTypeObject PyUnicode_Type = {
 
 void _PyUnicode_Init(void)
 {
+    int i;
+
     /* Doublecheck the configuration... */
     if (sizeof(Py_UNICODE) != 2)
         Py_FatalError("Unicode configuration error: "
@@ -5199,6 +5221,9 @@ void _PyUnicode_Init(void)
     unicode_freelist_size = 0;
     unicode_empty = _PyUnicode_New(0);
     strcpy(unicode_default_encoding, "ascii");
+
+    for (i = 0; i < 128; i++)
+	unicode_ascii[i] = NULL;
 }
 
 /* Finalize the Unicode implementation */
@@ -5207,10 +5232,18 @@ void
 _PyUnicode_Fini(void)
 {
     PyUnicodeObject *u;
+    int i;
 
     Py_XDECREF(unicode_empty);
     unicode_empty = NULL;
 
+    for (i = 0; i < 128; i++) {
+	if (unicode_ascii[i]) {
+	    Py_DECREF(unicode_ascii[i]);
+	    unicode_ascii[i] = NULL;
+	}
+    }
+
     for (u = unicode_freelist; u != NULL;) {
 	PyUnicodeObject *v = u;
 	u = *(PyUnicodeObject **)u;