diff --git a/Misc/NEWS.d/next/Library/2022-05-22-23-46-18.gh-issue-93033.wZfiL-.rst b/Misc/NEWS.d/next/Library/2022-05-22-23-46-18.gh-issue-93033.wZfiL-.rst
@@ -0,0 +1 @@
+Search in some strings (platform dependent i.e [U+0xFFFF, U+0x0100] on Windows or [U+0xFFFFFFFF, U+0x00010000] on Linux 64-bit) are now up to 10 times faster.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
@@ -1096,6 +1096,7 @@ bytearray_dealloc(PyByteArrayObject *self)
 #define STRINGLIB_ISSPACE Py_ISSPACE
 #define STRINGLIB_ISLINEBREAK(x) ((x == '\n') || (x == '\r'))
 #define STRINGLIB_CHECK_EXACT PyByteArray_CheckExact
+#define STRINGLIB_FAST_MEMCHR memchr
 #define STRINGLIB_MUTABLE 1
 
 #include "stringlib/fastsearch.h"

diff --git a/Objects/bytes_methods.c b/Objects/bytes_methods.c
@@ -431,6 +431,7 @@ _Py_bytes_maketrans(Py_buffer *frm, Py_buffer *to)
 #define STRINGLIB(F) stringlib_##F
 #define STRINGLIB_CHAR char
 #define STRINGLIB_SIZEOF_CHAR 1
+#define STRINGLIB_FAST_MEMCHR memchr
 
 #include "stringlib/fastsearch.h"
 #include "stringlib/count.h"

diff --git a/Objects/stringlib/asciilib.h b/Objects/stringlib/asciilib.h
@@ -21,6 +21,7 @@
 #define STRINGLIB_CHECK          PyUnicode_Check
 #define STRINGLIB_CHECK_EXACT    PyUnicode_CheckExact
 #define STRINGLIB_MUTABLE 0
+#define STRINGLIB_FAST_MEMCHR    memchr
 
 #define STRINGLIB_TOSTR          PyObject_Str
 #define STRINGLIB_TOASCII        PyObject_ASCII
diff --git a/Objects/stringlib/fastsearch.h b/Objects/stringlib/fastsearch.h
@@ -39,7 +39,7 @@
 #define STRINGLIB_BLOOM(mask, ch)     \
     ((mask &  (1UL << ((ch) & (STRINGLIB_BLOOM_WIDTH -1)))))
 
-#if STRINGLIB_SIZEOF_CHAR == 1
+#ifdef STRINGLIB_FAST_MEMCHR
 #  define MEMCHR_CUT_OFF 15
 #else
 #  define MEMCHR_CUT_OFF 40
@@ -53,8 +53,8 @@ STRINGLIB(find_char)(const STRINGLIB_CHAR* s, Py_ssize_t n, STRINGLIB_CHAR ch)
     p = s;
     e = s + n;
     if (n > MEMCHR_CUT_OFF) {
-#if STRINGLIB_SIZEOF_CHAR == 1
-        p = memchr(s, ch, n);
+#ifdef STRINGLIB_FAST_MEMCHR
+        p = STRINGLIB_FAST_MEMCHR(s, ch, n);
         if (p != NULL)
             return (p - s);
         return -1;
@@ -102,16 +102,26 @@ STRINGLIB(find_char)(const STRINGLIB_CHAR* s, Py_ssize_t n, STRINGLIB_CHAR ch)
     return -1;
 }
 
+#undef MEMCHR_CUT_OFF
+
+#if STRINGLIB_SIZEOF_CHAR == 1
+#  define MEMRCHR_CUT_OFF 15
+#else
+#  define MEMRCHR_CUT_OFF 40
+#endif
+
+
 Py_LOCAL_INLINE(Py_ssize_t)
 STRINGLIB(rfind_char)(const STRINGLIB_CHAR* s, Py_ssize_t n, STRINGLIB_CHAR ch)
 {
     const STRINGLIB_CHAR *p;
 #ifdef HAVE_MEMRCHR
-    /* memrchr() is a GNU extension, available since glibc 2.1.91.
-       it doesn't seem as optimized as memchr(), but is still quite
-       faster than our hand-written loop below */
+    /* memrchr() is a GNU extension, available since glibc 2.1.91.  it
+       doesn't seem as optimized as memchr(), but is still quite
+       faster than our hand-written loop below. There is no wmemrchr
+       for 4-byte chars. */
 
-    if (n > MEMCHR_CUT_OFF) {
+    if (n > MEMRCHR_CUT_OFF) {
 #if STRINGLIB_SIZEOF_CHAR == 1
         p = memrchr(s, ch, n);
         if (p != NULL)
@@ -139,19 +149,19 @@ STRINGLIB(rfind_char)(const STRINGLIB_CHAR* s, Py_ssize_t n, STRINGLIB_CHAR ch)
                 if (*p == ch)
                     return n;
                 /* False positive */
-                if (n1 - n > MEMCHR_CUT_OFF)
+                if (n1 - n > MEMRCHR_CUT_OFF)
                     continue;
-                if (n <= MEMCHR_CUT_OFF)
+                if (n <= MEMRCHR_CUT_OFF)
                     break;
-                s1 = p - MEMCHR_CUT_OFF;
+                s1 = p - MEMRCHR_CUT_OFF;
                 while (p > s1) {
                     p--;
                     if (*p == ch)
                         return (p - s);
                 }
                 n = p - s;
             }
-            while (n > MEMCHR_CUT_OFF);
+            while (n > MEMRCHR_CUT_OFF);
         }
 #endif
     }
@@ -165,7 +175,7 @@ STRINGLIB(rfind_char)(const STRINGLIB_CHAR* s, Py_ssize_t n, STRINGLIB_CHAR ch)
     return -1;
 }
 
-#undef MEMCHR_CUT_OFF
+#undef MEMRCHR_CUT_OFF
 
 /* Change to a 1 to see logging comments walk through the algorithm. */
 #if 0 && STRINGLIB_SIZEOF_CHAR == 1

diff --git a/Objects/stringlib/replace.h b/Objects/stringlib/replace.h
@@ -29,9 +29,9 @@ STRINGLIB(replace_1char_inplace)(STRINGLIB_CHAR* s, STRINGLIB_CHAR* end,
                 if (!--attempts) {
                     /* if u1 was not found for attempts iterations,
                        use FASTSEARCH() or memchr() */
-#if STRINGLIB_SIZEOF_CHAR == 1
+#ifdef STRINGLIB_FAST_MEMCHR
                     s++;
-                    s = memchr(s, u1, end - s);
+                    s = STRINGLIB_FAST_MEMCHR(s, u1, end - s);
                     if (s == NULL)
                         return;
 #else

diff --git a/Objects/stringlib/stringdefs.h b/Objects/stringlib/stringdefs.h
@@ -24,4 +24,5 @@
 #define STRINGLIB_CHECK_EXACT    PyBytes_CheckExact
 #define STRINGLIB_TOSTR          PyObject_Str
 #define STRINGLIB_TOASCII        PyObject_Repr
+#define STRINGLIB_FAST_MEMCHR    memchr
 #endif /* !STRINGLIB_STRINGDEFS_H */
diff --git a/Objects/stringlib/ucs1lib.h b/Objects/stringlib/ucs1lib.h
@@ -20,6 +20,7 @@
 #define STRINGLIB_NEW            _PyUnicode_FromUCS1
 #define STRINGLIB_CHECK          PyUnicode_Check
 #define STRINGLIB_CHECK_EXACT    PyUnicode_CheckExact
+#define STRINGLIB_FAST_MEMCHR    memchr
 #define STRINGLIB_MUTABLE 0
 
 #define STRINGLIB_TOSTR          PyObject_Str

diff --git a/Objects/stringlib/ucs2lib.h b/Objects/stringlib/ucs2lib.h
@@ -21,6 +21,10 @@
 #define STRINGLIB_CHECK          PyUnicode_Check
 #define STRINGLIB_CHECK_EXACT    PyUnicode_CheckExact
 #define STRINGLIB_MUTABLE 0
+#if SIZEOF_WCHAR_T == 2
+#define STRINGLIB_FAST_MEMCHR(s, c, n)              \
+    (Py_UCS2 *)wmemchr((const wchar_t *)(s), c, n)
+#endif
 
 #define STRINGLIB_TOSTR          PyObject_Str
 #define STRINGLIB_TOASCII        PyObject_ASCII
diff --git a/Objects/stringlib/ucs4lib.h b/Objects/stringlib/ucs4lib.h
@@ -21,6 +21,10 @@
 #define STRINGLIB_CHECK          PyUnicode_Check
 #define STRINGLIB_CHECK_EXACT    PyUnicode_CheckExact
 #define STRINGLIB_MUTABLE 0
+#if SIZEOF_WCHAR_T == 4
+#define STRINGLIB_FAST_MEMCHR(s, c, n)              \
+    (Py_UCS4 *)wmemchr((const wchar_t *)(s), c, n)
+#endif
 
 #define STRINGLIB_TOSTR          PyObject_Str
 #define STRINGLIB_TOASCII        PyObject_ASCII

diff --git a/Objects/stringlib/undef.h b/Objects/stringlib/undef.h
@@ -8,3 +8,4 @@
 #undef STRINGLIB_NEW
 #undef STRINGLIB_IS_UNICODE
 #undef STRINGLIB_MUTABLE
+#undef STRINGLIB_FAST_MEMCHR
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Search in some strings (platform dependent i.e [U+0xFFFF, U+0x0100] on Windows or [U+0xFFFFFFFF, U+0x00010000] on Linux 64-bit) are now up to 10 times faster.