--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -132,6 +132,7 @@ static int dbcs_char2cells(int c);
 static int dbcs_ptr2cells_len(char_u *p, int size);
 static int dbcs_ptr2char(char_u *p);
 static int dbcs_head_off(char_u *base, char_u *p);
+static int cw_value(int c);
 
 /*
  * Lookup table to quickly get the length in bytes of a UTF-8 character from
@@ -1487,7 +1488,7 @@ utf_char2cells(int c)
     // Sorted list of non-overlapping intervals of Emoji characters that don't
     // have ambiguous or double width,
     // based on http://unicode.org/emoji/charts/emoji-list.html
-    static struct interval emoji_width[] =
+    static struct interval emoji_wide[] =
     {
 	{0x1f1e6, 0x1f1ff},
 	{0x1f321, 0x1f321},
@@ -1532,12 +1533,18 @@ utf_char2cells(int c)
 
     if (c >= 0x100)
     {
+	int	n;
+
+	n = cw_value(c);
+	if (n != 0)
+	    return n;
+
 #ifdef USE_WCHAR_FUNCTIONS
 	/*
 	 * Assume the library function wcwidth() works better than our own
 	 * stuff.  It should return 1 for ambiguous width chars!
 	 */
-	int	n = wcwidth(c);
+	n = wcwidth(c);
 
 	if (n < 0)
 	    return 6;		// unprintable, displays <xxxx>
@@ -1549,7 +1556,7 @@ utf_char2cells(int c)
 	if (intable(doublewidth, sizeof(doublewidth), c))
 	    return 2;
 #endif
-	if (p_emoji && intable(emoji_width, sizeof(emoji_width), c))
+	if (p_emoji && intable(emoji_wide, sizeof(emoji_wide), c))
 	    return 2;
     }
 
@@ -2570,6 +2577,8 @@ utf_printable(int c)
 
 // Sorted list of non-overlapping intervals of all Emoji characters,
 // based on http://unicode.org/emoji/charts/emoji-list.html
+// Generated by ../runtime/tools/unicode.vim.
+// Excludes 0x00a9 and 0x00ae because they are considered latin1.
 static struct interval emoji_all[] =
 {
     {0x203c, 0x203c},
@@ -5342,3 +5351,177 @@ string_convert_ext(
 
     return retval;
 }
+
+/*
+ * Table set by setcellwidths().
+ */
+typedef struct
+{
+    long    first;
+    long    last;
+    char    width;
+} cw_interval_T;
+
+static cw_interval_T	*cw_table = NULL;
+static size_t		cw_table_size = 0;
+
+/*
+ * Return 1 or 2 when "c" is in the cellwidth table.
+ * Return 0 if not.
+ */
+    static int
+cw_value(int c)
+{
+    int mid, bot, top;
+
+    if (cw_table == NULL)
+	return 0;
+
+    // first quick check for Latin1 etc. characters
+    if (c < cw_table[0].first)
+	return 0;
+
+    // binary search in table
+    bot = 0;
+    top = (int)cw_table_size - 1;
+    while (top >= bot)
+    {
+	mid = (bot + top) / 2;
+	if (cw_table[mid].last < c)
+	    bot = mid + 1;
+	else if (cw_table[mid].first > c)
+	    top = mid - 1;
+	else
+	    return cw_table[mid].width;
+    }
+    return 0;
+}
+
+    static int
+tv_nr_compare(const void *a1, const void *a2)
+{
+    listitem_T *li1 = (listitem_T *)a1;
+    listitem_T *li2 = (listitem_T *)a2;
+
+    return li1->li_tv.vval.v_number - li2->li_tv.vval.v_number;
+}
+
+    void
+f_setcellwidths(typval_T *argvars, typval_T *rettv UNUSED)
+{
+    list_T	    *l;
+    listitem_T	    *li;
+    int		    item;
+    int		    i;
+    listitem_T	    **ptrs;
+    cw_interval_T   *table;
+
+    if (argvars[0].v_type != VAR_LIST || argvars[0].vval.v_list == NULL)
+    {
+	emsg(_(e_listreq));
+	return;
+    }
+    l = argvars[0].vval.v_list;
+    if (l->lv_len == 0)
+    {
+	// Clearing the table.
+	vim_free(cw_table);
+	cw_table = NULL;
+	cw_table_size = 0;
+	return;
+    }
+
+    ptrs = ALLOC_MULT(listitem_T *, l->lv_len);
+    if (ptrs == NULL)
+	return;
+
+    // Check that all entries are a list with three numbers, the range is
+    // valid and the cell width is valid.
+    item = 0;
+    for (li = l->lv_first; li != NULL; li = li->li_next)
+    {
+	listitem_T *lili;
+	varnumber_T n1;
+
+	if (li->li_tv.v_type != VAR_LIST || li->li_tv.vval.v_list == NULL)
+	{
+	    semsg(_(e_list_item_nr_is_not_list), item);
+	    vim_free(ptrs);
+	    return;
+	}
+	for (lili = li->li_tv.vval.v_list->lv_first, i = 0; lili != NULL;
+						     lili = lili->li_next, ++i)
+	{
+	    if (lili->li_tv.v_type != VAR_NUMBER)
+		break;
+	    if (i == 0)
+	    {
+		n1 = lili->li_tv.vval.v_number;
+		if (n1 < 0x100)
+		{
+		    emsg(_(e_only_values_of_0x100_and_higher_supported));
+		    vim_free(ptrs);
+		    return;
+		}
+	    }
+	    else if (i == 1 && lili->li_tv.vval.v_number < n1)
+	    {
+		semsg(_(e_list_item_nr_range_invalid), item);
+		vim_free(ptrs);
+		return;
+	    }
+	    else if (i == 2 && (lili->li_tv.vval.v_number < 1
+					     || lili->li_tv.vval.v_number > 2))
+	    {
+		semsg(_(e_list_item_nr_cell_width_invalid), item);
+		vim_free(ptrs);
+		return;
+	    }
+	}
+	if (i != 3)
+	{
+	    semsg(_(e_list_item_nr_does_not_contain_3_numbers), item);
+	    vim_free(ptrs);
+	    return;
+	}
+	ptrs[item++] = lili;
+    }
+
+    // Sort the list on the first number.
+    qsort((void *)ptrs, (size_t)l->lv_len, sizeof(listitem_T *), tv_nr_compare);
+
+    table = ALLOC_MULT(cw_interval_T, l->lv_len);
+    if (table == NULL)
+    {
+	vim_free(ptrs);
+	return;
+    }
+
+    // Store the items in the new table.
+    item = 0;
+    for (li = l->lv_first; li != NULL; li = li->li_next)
+    {
+	listitem_T	*lili = li->li_tv.vval.v_list->lv_first;
+	varnumber_T	n1;
+
+	n1 = lili->li_tv.vval.v_number;
+	if (item > 0 && n1 <= table[item - 1].last)
+	{
+	    semsg(_(e_overlapping_ranges_for_nr), (long)n1);
+	    vim_free(ptrs);
+	    vim_free(table);
+	    return;
+	}
+	table[item].first = n1;
+	lili = lili->li_next;
+	table[item].last = lili->li_tv.vval.v_number;
+	lili = lili->li_next;
+	table[item].width = lili->li_tv.vval.v_number;
+	++item;
+    }
+
+    vim_free(ptrs);
+    vim_free(cw_table);
+    cw_table = table;
+    cw_table_size = l->lv_len;
+}