gh-120196: Faster ascii_decode and find_max_char implementations

Objects/bytes_methods.c

@@ -92,57 +92,6 @@ _Py_bytes_isalnum(const char *cptr, Py_ssize_t len)
 }
 
 
-PyDoc_STRVAR_shared(_Py_isascii__doc__,
-"B.isascii() -> bool\n\
-\n\
-Return True if B is empty or all characters in B are ASCII,\n\
-False otherwise.");
-
-// Optimization is copied from ascii_decode in unicodeobject.c
-/* Mask to quickly check whether a C 'size_t' contains a
-   non-ASCII, UTF8-encoded char. */
-#if (SIZEOF_SIZE_T == 8)
-# define ASCII_CHAR_MASK 0x8080808080808080ULL
-#elif (SIZEOF_SIZE_T == 4)
-# define ASCII_CHAR_MASK 0x80808080U
-#else
-# error C 'size_t' size should be either 4 or 8!
-#endif
-
-PyObject*
-_Py_bytes_isascii(const char *cptr, Py_ssize_t len)
-{
-    const char *p = cptr;
-    const char *end = p + len;
-
-    while (p < end) {
-        /* Fast path, see in STRINGLIB(utf8_decode) in stringlib/codecs.h
-           for an explanation. */
-        if (_Py_IS_ALIGNED(p, ALIGNOF_SIZE_T)) {
-            /* Help allocation */
-            const char *_p = p;
-            while (_p + SIZEOF_SIZE_T <= end) {
-                size_t value = *(const size_t *) _p;
-                if (value & ASCII_CHAR_MASK) {
-                    Py_RETURN_FALSE;
-                }
-                _p += SIZEOF_SIZE_T;
-            }
-            p = _p;
-            if (_p == end)
-                break;
-        }
-        if ((unsigned char)*p & 0x80) {
-            Py_RETURN_FALSE;
-        }
-        p++;
-    }
-    Py_RETURN_TRUE;
-}
-
-#undef ASCII_CHAR_MASK
-
-
 PyDoc_STRVAR_shared(_Py_isdigit__doc__,
 "B.isdigit() -> bool\n\
 \n\
@@ -438,6 +387,7 @@ _Py_bytes_maketrans(Py_buffer *frm, Py_buffer *to)
 #include "stringlib/fastsearch.h"
 #include "stringlib/count.h"
 #include "stringlib/find.h"
+#include "stringlib/find_max_char.h"
 
 /*
 Wraps stringlib_parse_args_finds() and additionally checks the first
@@ -765,3 +715,21 @@ _Py_bytes_endswith(const char *str, Py_ssize_t len, PyObject *subobj,
 {
     return _Py_bytes_tailmatch(str, len, "endswith", subobj, start, end, +1);
 }
+
+PyDoc_STRVAR_shared(_Py_isascii__doc__,
+"B.isascii() -> bool\n\
+\n\
+Return True if B is empty or all characters in B are ASCII,\n\
+False otherwise.");
+
+PyObject*
+_Py_bytes_isascii(const char *cptr, Py_ssize_t len)
+{
+    const char *p = cptr;
+    const char *end = p + len;
+    Py_ssize_t max_char = stringlib_find_max_char(cptr, end);
+    if (max_char > 127) {
+        Py_RETURN_FALSE;
+    }
+    Py_RETURN_TRUE;
+}

Objects/stringlib/find_max_char.h

@@ -1,6 +1,7 @@
 /* Finding the optimal width of unicode characters in a buffer */
 
-#if !STRINGLIB_IS_UNICODE
+/* find_max_char for one-byte will work for bytes objects as well. */
+#if !STRINGLIB_IS_UNICODE && STRINGLIB_SIZEOF_CHAR > 1
 # error "find_max_char.h is specific to Unicode"
 #endif