diff --git a/Makefile.pre.in b/Makefile.pre.in
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -627,6 +627,7 @@ BYTESTR_DEPS = \
 		$(srcdir)/Objects/stringlib/eq.h \
 		$(srcdir)/Objects/stringlib/fastsearch.h \
 		$(srcdir)/Objects/stringlib/find.h \
+		$(srcdir)/Objects/stringlib/findwidth.h \
 		$(srcdir)/Objects/stringlib/partition.h \
 		$(srcdir)/Objects/stringlib/split.h \
 		$(srcdir)/Objects/stringlib/stringdefs.h \
diff --git a/Objects/stringlib/findwidth.h b/Objects/stringlib/findwidth.h
new file mode 100644
--- /dev/null
+++ b/Objects/stringlib/findwidth.h
@@ -0,0 +1,124 @@
+/* Finding the optimal width of unicode characters in a buffer */
+
+#if STRINGLIB_IS_UNICODE
+
+/* Mask to check or force alignment of a pointer to C 'long' boundaries */
+#define LONG_PTR_MASK (size_t) (SIZEOF_LONG - 1)
+
+/* Mask to quickly check whether a C 'long' contains a
+   non-ASCII, UTF8-encoded char. */
+#if (SIZEOF_LONG == 8)
+# define UCS1_ASCII_CHAR_MASK 0x8080808080808080L
+#elif (SIZEOF_LONG == 4)
+# define UCS1_ASCII_CHAR_MASK 0x80808080L
+#else
+# error C 'long' size should be either 4 or 8!
+#endif
+
+#if STRINGLIB_SIZEOF_CHAR == 1
+
+Py_LOCAL_INLINE(Py_UCS4)
+STRINGLIB(find_max_char)(const STRINGLIB_CHAR *begin, const STRINGLIB_CHAR *end)
+{
+    const unsigned char *p = (const unsigned char *) begin;
+    const unsigned char *aligned_end = (const unsigned char *) ((size_t) end & ~LONG_PTR_MASK);
+
+    while (p < end) {
+        if (!((size_t) p & LONG_PTR_MASK)) {
+            /* Help register allocation */
+            register const unsigned char *_p = p;
+            while (_p < aligned_end) {
+                unsigned long value = *(unsigned long *) _p;
+                if (value & UCS1_ASCII_CHAR_MASK)
+                    return 255;
+                _p += SIZEOF_LONG;
+            }
+            p = _p;
+            if (p == end)
+                break;
+        }
+        if (*p++ & 0x80)
+            return 255;
+    }
+    return 127;
+}
+
+#undef LONG_PTR_MASK
+#undef ASCII_CHAR_MASK
+
+#else /* STRINGLIB_SIZEOF_CHAR == 1 */
+
+#define MASK_ASCII 0xFFFFFF80
+#define MASK_UCS1 0xFFFFFF00
+#define MASK_UCS2 0xFFFF0000
+
+Py_LOCAL_INLINE(Py_UCS4)
+STRINGLIB(find_max_char)(const STRINGLIB_CHAR *begin, const STRINGLIB_CHAR *end)
+{
+#if STRINGLIB_SIZEOF_CHAR == 2
+    const Py_UCS4 mask_limit = MASK_UCS1;
+#elif STRINGLIB_SIZEOF_CHAR == 4
+    const Py_UCS4 mask_limit = MASK_UCS2;
+#else
+#error Invalid STRINGLIB_SIZEOF_CHAR (must be 1, 2 or 4)
+#endif
+    register Py_UCS4 mask = MASK_ASCII;
+    Py_UCS4 ret;
+
+    const STRINGLIB_CHAR *p = begin;
+    Py_ssize_t n = end - begin;
+    const STRINGLIB_CHAR *unrolled_end = begin + (n & ~ (Py_ssize_t) 7);
+    while (p < unrolled_end) {
+        Py_UCS4 bits = p[0] | p[1] | p[2] | p[3];
+_recheck:
+        if (bits & mask) {
+            if (mask == mask_limit) {
+                /* Limit reached */
+                ret = ~mask + 1;
+                goto _end;
+            }
+            if (mask == MASK_ASCII) {
+                mask = MASK_UCS1;
+            }
+            else {
+                /* mask can't be MASK_UCS2 because of mask_limit above */
+                assert(mask == MASK_UCS1);
+                mask = MASK_UCS2;
+            }
+            goto _recheck;
+            /* We check the new mask on the same chars in the next iteration */
+            continue;
+        }
+        p += 4;
+    }
+    while (p < end) {
+        if (p[0] & mask) {
+            if (mask == mask_limit) {
+                /* Limit reached */
+                ret = ~mask + 1;
+                goto _end;
+            }
+            if (mask == MASK_ASCII) {
+                mask = MASK_UCS1;
+            }
+            else {
+                /* mask can't be MASK_UCS2 because of mask_limit above */
+                assert(mask == MASK_UCS1);
+                mask = MASK_UCS2;
+            }
+            /* We check the new mask on the same chars in the next iteration */
+            continue;
+        }
+        p++;
+    }
+    ret = ~mask;
+_end:
+    if (ret >= 0x10FFFF)
+        return 0x10FFFF;
+    else
+        return ret;
+}
+
+#endif /* STRINGLIB_SIZEOF_CHAR == 1 */
+#endif /* STRINGLIB_IS_UNICODE */
+
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -260,6 +260,15 @@ static int unicode_is_singleton(PyObject
 #endif
 
 static PyObject *
+unicode_fromascii(const unsigned char *s, Py_ssize_t size);
+static PyObject *
+_PyUnicode_FromUCS1(const unsigned char *s, Py_ssize_t size);
+static PyObject *
+_PyUnicode_FromUCS2(const Py_UCS2 *s, Py_ssize_t size);
+static PyObject *
+_PyUnicode_FromUCS4(const Py_UCS4 *s, Py_ssize_t size);
+
+static PyObject *
 unicode_encode_call_errorhandler(const char *errors,
        PyObject **errorHandler,const char *encoding, const char *reason,
        const Py_UNICODE *unicode, Py_ssize_t size, PyObject **exceptionObject,
@@ -468,6 +477,48 @@ make_bloom_mask(int kind, void* ptr, Py_
     (BLOOM(mask, chr) \
      && (PyUnicode_FindChar(str, chr, 0, PyUnicode_GET_LENGTH(str), 1) >= 0))
 
+/* Compilation of templated routines */
+
+#include "stringlib/asciilib.h"
+#include "stringlib/fastsearch.h"
+#include "stringlib/partition.h"
+#include "stringlib/split.h"
+#include "stringlib/count.h"
+#include "stringlib/find.h"
+#include "stringlib/findwidth.h"
+#include "stringlib/localeutil.h"
+#include "stringlib/undef.h"
+
+#include "stringlib/ucs1lib.h"
+#include "stringlib/fastsearch.h"
+#include "stringlib/partition.h"
+#include "stringlib/split.h"
+#include "stringlib/count.h"
+#include "stringlib/find.h"
+#include "stringlib/findwidth.h"
+#include "stringlib/localeutil.h"
+#include "stringlib/undef.h"
+
+#include "stringlib/ucs2lib.h"
+#include "stringlib/fastsearch.h"
+#include "stringlib/partition.h"
+#include "stringlib/split.h"
+#include "stringlib/count.h"
+#include "stringlib/find.h"
+#include "stringlib/findwidth.h"
+#include "stringlib/localeutil.h"
+#include "stringlib/undef.h"
+
+#include "stringlib/ucs4lib.h"
+#include "stringlib/fastsearch.h"
+#include "stringlib/partition.h"
+#include "stringlib/split.h"
+#include "stringlib/count.h"
+#include "stringlib/find.h"
+#include "stringlib/findwidth.h"
+#include "stringlib/localeutil.h"
+#include "stringlib/undef.h"
+
 /* --- Unicode Object ----------------------------------------------------- */
 
 static PyObject *
@@ -1689,17 +1740,11 @@ _PyUnicode_FromUCS1(const unsigned char*
 {
     PyObject *res;
     unsigned char max_char = 127;
-    Py_ssize_t i;
 
     assert(size >= 0);
     if (size == 1)
         return get_latin1_char(u[0]);
-    for (i = 0; i < size; i++) {
-        if (u[i] & 0x80) {
-            max_char = 255;
-            break;
-        }
-    }
+    max_char = ucs1lib_find_max_char(u, u + size);
     res = PyUnicode_New(size, max_char);
     if (!res)
         return NULL;
@@ -1713,26 +1758,20 @@ _PyUnicode_FromUCS2(const Py_UCS2 *u, Py
 {
     PyObject *res;
     Py_UCS2 max_char = 0;
-    Py_ssize_t i;
 
     assert(size >= 0);
     if (size == 1 && u[0] < 256)
         return get_latin1_char((unsigned char)u[0]);
-    for (i = 0; i < size; i++) {
-        if (u[i] > max_char) {
-            max_char = u[i];
-            if (max_char >= 256)
-                break;
-        }
-    }
+    max_char = ucs2lib_find_max_char(u, u + size);
     res = PyUnicode_New(size, max_char);
     if (!res)
         return NULL;
     if (max_char >= 256)
         memcpy(PyUnicode_2BYTE_DATA(res), u, sizeof(Py_UCS2)*size);
-    else
-        for (i = 0; i < size; i++)
-            PyUnicode_1BYTE_DATA(res)[i] = (Py_UCS1)u[i];
+    else {
+        _PyUnicode_CONVERT_BYTES(
+            Py_UCS2, Py_UCS1, u, u + size, PyUnicode_1BYTE_DATA(res));
+    }
     assert(_PyUnicode_CheckConsistency(res, 1));
     return res;
 }
@@ -1742,18 +1781,11 @@ _PyUnicode_FromUCS4(const Py_UCS4 *u, Py
 {
     PyObject *res;
     Py_UCS4 max_char = 0;
-    Py_ssize_t i;
 
     assert(size >= 0);
     if (size == 1 && u[0] < 256)
         return get_latin1_char(u[0]);
-    for (i = 0; i < size; i++) {
-        if (u[i] > max_char) {
-            max_char = u[i];
-            if (max_char >= 0x10000)
-                break;
-        }
-    }
+    max_char = ucs4lib_find_max_char(u, u + size);
     res = PyUnicode_New(size, max_char);
     if (!res)
         return NULL;
@@ -1794,7 +1826,7 @@ unicode_adjust_maxchar(PyObject **p_unic
 {
     PyObject *unicode, *copy;
     Py_UCS4 max_char;
-    Py_ssize_t i, len;
+    Py_ssize_t len;
     unsigned int kind;
 
     assert(p_unicode != NULL);
@@ -1807,37 +1839,23 @@ unicode_adjust_maxchar(PyObject **p_unic
     kind = PyUnicode_KIND(unicode);
     if (kind == PyUnicode_1BYTE_KIND) {
         const Py_UCS1 *u = PyUnicode_1BYTE_DATA(unicode);
-        for (i = 0; i < len; i++) {
-            if (u[i] & 0x80)
-                return;
-        }
-        max_char = 127;
+        max_char = ucs1lib_find_max_char(u, u + len);
+        if (max_char >= 128)
+            return;
     }
     else if (kind == PyUnicode_2BYTE_KIND) {
         const Py_UCS2 *u = PyUnicode_2BYTE_DATA(unicode);
-        max_char = 0;
-        for (i = 0; i < len; i++) {
-            if (u[i] > max_char) {
-                max_char = u[i];
-                if (max_char >= 256)
-                    return;
-            }
-        }
+        max_char = ucs2lib_find_max_char(u, u + len);
+        if (max_char >= 256)
+            return;
     }
     else {
-        const Py_UCS4 *u;
+        const Py_UCS4 *u = PyUnicode_4BYTE_DATA(unicode);
         assert(kind == PyUnicode_4BYTE_KIND);
-        u = PyUnicode_4BYTE_DATA(unicode);
-        max_char = 0;
-        for (i = 0; i < len; i++) {
-            if (u[i] > max_char) {
-                max_char = u[i];
-                if (max_char >= 0x10000)
-                    return;
-            }
-        }
-    }
-    assert(max_char < PyUnicode_MAX_CHAR_VALUE(unicode));
+        max_char = ucs4lib_find_max_char(u, u + len);
+        if (max_char >= 0x10000)
+            return;
+    }
     copy = PyUnicode_New(len, max_char);
     copy_characters(copy, 0, unicode, 0, len);
     Py_DECREF(unicode);
@@ -8508,42 +8526,6 @@ PyUnicode_EncodeDecimal(Py_UNICODE *s,
 
 /* --- Helpers ------------------------------------------------------------ */
 
-#include "stringlib/asciilib.h"
-#include "stringlib/fastsearch.h"
-#include "stringlib/partition.h"
-#include "stringlib/split.h"
-#include "stringlib/count.h"
-#include "stringlib/find.h"
-#include "stringlib/localeutil.h"
-#include "stringlib/undef.h"
-
-#include "stringlib/ucs1lib.h"
-#include "stringlib/fastsearch.h"
-#include "stringlib/partition.h"
-#include "stringlib/split.h"
-#include "stringlib/count.h"
-#include "stringlib/find.h"
-#include "stringlib/localeutil.h"
-#include "stringlib/undef.h"
-
-#include "stringlib/ucs2lib.h"
-#include "stringlib/fastsearch.h"
-#include "stringlib/partition.h"
-#include "stringlib/split.h"
-#include "stringlib/count.h"
-#include "stringlib/find.h"
-#include "stringlib/localeutil.h"
-#include "stringlib/undef.h"
-
-#include "stringlib/ucs4lib.h"
-#include "stringlib/fastsearch.h"
-#include "stringlib/partition.h"
-#include "stringlib/split.h"
-#include "stringlib/count.h"
-#include "stringlib/find.h"
-#include "stringlib/localeutil.h"
-#include "stringlib/undef.h"
-
 static Py_ssize_t
 any_find_slice(int direction, PyObject* s1, PyObject* s2,
                Py_ssize_t start,