Perform build and magnum tuning

Building o//third_party/python now takes 5 seconds on my PC

This change works towards modifying Python to use runtime dispatching
when appropriate. For example, when loading the magnums in the socket
module, it's a good idea to check if the magnum is zero, because that
means the local system platform doesn't support it.

third_party/python/Objects/stringlib/find.inc

@@ -0,0 +1,120 @@
+/* clang-format off */
+/* stringlib: find/index implementation */
+
+#ifndef STRINGLIB_FASTSEARCH_H
+#error must include fastsearch.inc before including this module
+#endif
+
+Py_LOCAL_INLINE(Py_ssize_t)
+STRINGLIB(find)(const STRINGLIB_CHAR* str, Py_ssize_t str_len,
+               const STRINGLIB_CHAR* sub, Py_ssize_t sub_len,
+               Py_ssize_t offset)
+{
+    Py_ssize_t pos;
+
+    assert(str_len >= 0);
+    if (sub_len == 0)
+        return offset;
+
+    pos = FASTSEARCH(str, str_len, sub, sub_len, -1, FAST_SEARCH);
+
+    if (pos >= 0)
+        pos += offset;
+
+    return pos;
+}
+
+Py_LOCAL_INLINE(Py_ssize_t)
+STRINGLIB(rfind)(const STRINGLIB_CHAR* str, Py_ssize_t str_len,
+                const STRINGLIB_CHAR* sub, Py_ssize_t sub_len,
+                Py_ssize_t offset)
+{
+    Py_ssize_t pos;
+
+    assert(str_len >= 0);
+    if (sub_len == 0)
+        return str_len + offset;
+
+    pos = FASTSEARCH(str, str_len, sub, sub_len, -1, FAST_RSEARCH);
+
+    if (pos >= 0)
+        pos += offset;
+
+    return pos;
+}
+
+Py_LOCAL_INLINE(Py_ssize_t)
+STRINGLIB(find_slice)(const STRINGLIB_CHAR* str, Py_ssize_t str_len,
+                     const STRINGLIB_CHAR* sub, Py_ssize_t sub_len,
+                     Py_ssize_t start, Py_ssize_t end)
+{
+    return STRINGLIB(find)(str + start, end - start, sub, sub_len, start);
+}
+
+Py_LOCAL_INLINE(Py_ssize_t)
+STRINGLIB(rfind_slice)(const STRINGLIB_CHAR* str, Py_ssize_t str_len,
+                      const STRINGLIB_CHAR* sub, Py_ssize_t sub_len,
+                      Py_ssize_t start, Py_ssize_t end)
+{
+    return STRINGLIB(rfind)(str + start, end - start, sub, sub_len, start);
+}
+
+#ifdef STRINGLIB_WANT_CONTAINS_OBJ
+
+Py_LOCAL_INLINE(int)
+STRINGLIB(contains_obj)(PyObject* str, PyObject* sub)
+{
+    return STRINGLIB(find)(
+        STRINGLIB_STR(str), STRINGLIB_LEN(str),
+        STRINGLIB_STR(sub), STRINGLIB_LEN(sub), 0
+        ) != -1;
+}
+
+#endif /* STRINGLIB_WANT_CONTAINS_OBJ */
+
+/*
+This function is a helper for the "find" family (find, rfind, index,
+rindex) and for count, startswith and endswith, because they all have
+the same behaviour for the arguments.
+
+It does not touch the variables received until it knows everything
+is ok.
+*/
+
+#define FORMAT_BUFFER_SIZE 50
+
+Py_LOCAL_INLINE(int)
+STRINGLIB(parse_args_finds)(const char * function_name, PyObject *args,
+                           PyObject **subobj,
+                           Py_ssize_t *start, Py_ssize_t *end)
+{
+    PyObject *tmp_subobj;
+    Py_ssize_t tmp_start = 0;
+    Py_ssize_t tmp_end = PY_SSIZE_T_MAX;
+    PyObject *obj_start=Py_None, *obj_end=Py_None;
+    char format[FORMAT_BUFFER_SIZE] = "O|OO:";
+    size_t len = strlen(format);
+
+    strncpy(format + len, function_name, FORMAT_BUFFER_SIZE - len - 1);
+    format[FORMAT_BUFFER_SIZE - 1] = '\0';
+
+    if (!PyArg_ParseTuple(args, format, &tmp_subobj, &obj_start, &obj_end))
+        return 0;
+
+    /* To support None in "start" and "end" arguments, meaning
+       the same as if they were not passed.
+    */
+    if (obj_start != Py_None)
+        if (!_PyEval_SliceIndex(obj_start, &tmp_start))
+            return 0;
+    if (obj_end != Py_None)
+        if (!_PyEval_SliceIndex(obj_end, &tmp_end))
+            return 0;
+
+    *start = tmp_start;
+    *end = tmp_end;
+    *subobj = tmp_subobj;
+    return 1;
+}
+
+#undef FORMAT_BUFFER_SIZE