1 files changed, 30 insertions, 7 deletions

diff --git a/src/coding.c b/src/coding.c
index 0bea2a0c2bc..49c1e625d57 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -9471,6 +9471,17 @@ not fully specified.)  */)
   return code_convert_region (start, end, coding_system, destination, 1, 0);
 }
 
+/* Whether a string only contains chars in the 0..127 range.  */
+static bool
+string_ascii_p (Lisp_Object str)
+{
+  ptrdiff_t nbytes = SBYTES (str);
+  for (ptrdiff_t i = 0; i < nbytes; i++)
+    if (SREF (str, i) > 127)
+      return false;
+  return true;
+}
+
 Lisp_Object
 code_convert_string (Lisp_Object string, Lisp_Object coding_system,
                      Lisp_Object dst_object, bool encodep, bool nocopy,
@@ -9485,7 +9496,7 @@ code_convert_string (Lisp_Object string, Lisp_Object coding_system,
       if (! norecord)
         Vlast_coding_system_used = Qno_conversion;
       if (NILP (dst_object))
-        return (nocopy ? Fcopy_sequence (string) : string);
+        return nocopy ? string : Fcopy_sequence (string);
     }
 
   if (NILP (coding_system))
@@ -9502,7 +9513,21 @@ code_convert_string (Lisp_Object string, Lisp_Object coding_system,
   chars = SCHARS (string);
   bytes = SBYTES (string);
 
-  if (BUFFERP (dst_object))
+  if (EQ (dst_object, Qt))
+    {
+      /* Fast path for ASCII-only input and an ASCII-compatible coding:
+         act as identity.  */
+      Lisp_Object attrs = CODING_ID_ATTRS (coding.id);
+      if (! NILP (CODING_ATTR_ASCII_COMPAT (attrs))
+          && (STRING_MULTIBYTE (string)
+              ? (chars == bytes) : string_ascii_p (string)))
+        return (nocopy
+                ? string
+                : (encodep
+                   ? make_unibyte_string (SSDATA (string), bytes)
+                   : make_multibyte_string (SSDATA (string), bytes, bytes)));
+    }
+  else if (BUFFERP (dst_object))
     {
       struct buffer *buf = XBUFFER (dst_object);
       ptrdiff_t buf_pt = BUF_PT (buf);
@@ -11061,10 +11086,8 @@ usage: (define-coding-system-internal ...)  */)
           else
             {
               CHECK_CONS (val);
-              CHECK_RANGED_INTEGER (XCAR (val), 0, 255);
-              from = XFIXNUM (XCAR (val));
-              CHECK_RANGED_INTEGER (XCDR (val), from, 255);
-              to = XFIXNUM (XCDR (val));
+              from = check_integer_range (XCAR (val), 0, 255);
+              to = check_integer_range (XCDR (val), from, 255);
             }
           for (int i = from; i <= to; i++)
             SSET (valids, i, 1);
@@ -11149,7 +11172,7 @@ usage: (define-coding-system-internal ...)  */)
           val = XCAR (tail);
           CHECK_CONS (val);
           CHECK_CHARSET_GET_ID (XCAR (val), id);
-          CHECK_RANGED_INTEGER (XCDR (val), 0, 3);
+          check_integer_range (XCDR (val), 0, 3);
           XSETCAR (val, make_fixnum (id));
         }