+/* Return width of Lisp string STRING when displayed in the current
+ buffer. The width is measured by how many columns it occupies on
+ the screen while paying attention to compositions. If PRECISION >
+ 0, return the width of longest substring that doesn't exceed
+ PRECISION, and set number of characters and bytes of the substring
+ in *NCHARS and *NBYTES respectively. */
+
+int
+lisp_string_width (string, precision, nchars, nbytes)
+ Lisp_Object string;
+ int precision, *nchars, *nbytes;
+{
+ int len = SCHARS (string);
+ int len_byte = SBYTES (string);
+ /* This set multibyte to 0 even if STRING is multibyte when it
+ contains only ascii and eight-bit-graphic, but that's
+ intentional. */
+ int multibyte = len < len_byte;
+ const unsigned char *str = SDATA (string);
+ int i = 0, i_byte = 0;
+ int width = 0;
+ struct Lisp_Char_Table *dp = buffer_display_table ();
+
+ while (i < len)
+ {
+ int chars, bytes, thiswidth;
+ Lisp_Object val;
+ int cmp_id;
+ int ignore, end;
+
+ if (find_composition (i, -1, &ignore, &end, &val, string)
+ && ((cmp_id = get_composition_id (i, i_byte, end - i, val, string))
+ >= 0))
+ {
+ thiswidth = composition_table[cmp_id]->width;
+ chars = end - i;
+ bytes = string_char_to_byte (string, end) - i_byte;
+ }
+ else if (dp)
+ {
+ int c;
+
+ if (multibyte)
+ c = STRING_CHAR_AND_LENGTH (str + i_byte, len - i_byte, bytes);
+ else
+ c = str[i_byte], bytes = 1;
+ chars = 1;
+ val = DISP_CHAR_VECTOR (dp, c);
+ if (VECTORP (val))
+ thiswidth = XVECTOR (val)->size;
+ else
+ thiswidth = ONE_BYTE_CHAR_WIDTH (str[i_byte]);
+ }