Speedup str[a:b:step] for step != 1
Try to stop the scanner of the maximum character before the end using a limit
depending on the kind (e.g. 256 for PyUnicode_2BYTE_KIND).
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 93459a7..417f955 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1520,6 +1520,22 @@
return res;
}
+static Py_UCS4
+kind_maxchar_limit(unsigned int kind)
+{
+ switch(kind) {
+ case PyUnicode_1BYTE_KIND:
+ return 0x80;
+ case PyUnicode_2BYTE_KIND:
+ return 0x100;
+ case PyUnicode_4BYTE_KIND:
+ return 0x10000;
+ default:
+ assert(0 && "invalid kind");
+ return 0x10ffff;
+ }
+}
+
static PyObject*
_PyUnicode_FromUCS1(const unsigned char* u, Py_ssize_t size)
{
@@ -12335,7 +12351,7 @@
PyObject *result;
void *src_data, *dest_data;
int src_kind, dest_kind;
- Py_UCS4 ch, max_char;
+ Py_UCS4 ch, max_char, kind_limit;
if (PySlice_GetIndicesEx(item, PyUnicode_GET_LENGTH(self),
&start, &stop, &step, &slicelength) < 0) {
@@ -12354,13 +12370,17 @@
start, start + slicelength);
}
/* General case */
- max_char = 127;
+ max_char = 0;
src_kind = PyUnicode_KIND(self);
+ kind_limit = kind_maxchar_limit(src_kind);
src_data = PyUnicode_DATA(self);
for (cur = start, i = 0; i < slicelength; cur += step, i++) {
ch = PyUnicode_READ(src_kind, src_data, cur);
- if (ch > max_char)
+ if (ch > max_char) {
max_char = ch;
+ if (max_char >= kind_limit)
+ break;
+ }
}
result = PyUnicode_New(slicelength, max_char);
if (result == NULL)