(Qas, Qmake, Qto): New variables.

(Fset_buffer_multibyte): New optional arg METHOD.  Caller changed.
(syms_of_buffer): Intern and staticpro Qas, Qmake, and Qto.

1 files changed, 65 insertions, 11 deletions

diff --git a/src/buffer.c b/src/buffer.c
index f050305de59..b00bb5b06c2 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2012,15 +2012,30 @@ advance_to_char_boundary (byte_pos)
   return byte_pos;
 }
 
+
+/* Symbols used as the 2nd arg of Fset_buffer_multibyte.  */
+static Lisp_Object Qas, Qmake, Qto;
+
+
 DEFUN ("set-buffer-multibyte", Fset_buffer_multibyte, Sset_buffer_multibyte,
-       1, 1, 0,
+       1, 2, 0,
        doc: /* Set the multibyte flag of the current buffer to FLAG.
 If FLAG is t, this makes the buffer a multibyte buffer.
-If FLAG is nil, this makes the buffer a single-byte buffer.
-The buffer contents remain unchanged as a sequence of bytes
-but the contents viewed as characters do change.  */)
-     (flag)
-     Lisp_Object flag;
+If FLAG is nil, this makes the buffer a unibyte buffer.
+
+Optional second arg METHOD specifies how to convert the byte sequence
+of the buffer.
+
+If it is nil or `as', the buffer contents remain unchanged as a
+sequence of bytes but the contents viewed as characters do change.
+
+If it is `make', convert each character by unibyte-char-to-multibyte
+or multibyte-char-to-unibyte.
+
+If it is `to', convert each character by byte-to-char or
+char-to-byte.  */)
+     (flag, method)
+     Lisp_Object flag, method;
 {
   Lisp_Object tail, markers;
   struct buffer *other;
@@ -2029,6 +2044,13 @@ but the contents viewed as characters do change.  */)
   int narrowed = (BEG != begv || Z != zv);
   int modified_p = !NILP (Fbuffer_modified_p (Qnil));
 
+  CHECK_SYMBOL (method);
+  if (NILP (method))
+    method = Qas;
+  else if (! EQ (method, Qas) && ! EQ (method, Qmake) && ! EQ (method, Qto))
+    error ("Invalid unibyte<->multibyte conversion method: %s",
+           XSYMBOL (method)->name->data);
+
   if (current_buffer->base_buffer)
     error ("Cannot do `set-buffer-multibyte' on an indirect buffer");
 
@@ -2105,11 +2127,27 @@ but the contents viewed as characters do change.  */)
                 zv -= bytes;
               stop = Z;
             }
-          else
+          else if (EQ (method, Qas))
             {
               bytes = BYTES_BY_CHAR_HEAD (*p);
               p += bytes, pos += bytes;
             }
+          else
+            {
+              /* Delete all bytes for this character but the last one,
+                 and change the last one to the unibyte code.  */
+              c = STRING_CHAR_AND_LENGTH (p, stop - pos, bytes);
+              bytes--;
+              del_range_2 (pos, pos, pos + bytes, pos + bytes, 0);
+              p = GAP_END_ADDR;
+              *p++ = CHAR_TO_BYTE (c);
+              pos++;
+              if (begv > pos)
+                begv -= bytes;
+              if (zv > pos)
+                zv -= bytes;
+              stop = Z;
+            }
         }
       if (narrowed)
         Fnarrow_to_region (make_number (begv), make_number (zv));
@@ -2124,7 +2162,8 @@ but the contents viewed as characters do change.  */)
          Ex: We change this: "...abc\302 _GAP_ \241def..."
              to: "...abc _GAP_ \302\241def..."  */
 
-      if (GPT_BYTE > 1 && GPT_BYTE < Z_BYTE
+      if (EQ (method, Qas)
+          && GPT_BYTE > 1 && GPT_BYTE < Z_BYTE
           && ! CHAR_HEAD_P (*(GAP_END_ADDR)))
         {
           unsigned char *p = GPT_ADDR - 1;
@@ -2157,12 +2196,20 @@ but the contents viewed as characters do change.  */)
               stop = Z;
             }
               
-          if ((bytes = MULTIBYTE_LENGTH (p, pend)) > 0)
+          if (ASCII_BYTE_P (*p))
+            p++, pos++;
+          else if (method == Qas
+                   && (bytes = MULTIBYTE_LENGTH (p, pend)) > 0)
             p += bytes, pos += bytes;
           else
             {
               unsigned char tmp[MAX_MULTIBYTE_LENGTH];
-              int c = BYTE8_TO_CHAR (*p);
+              int c;
+
+              if (method == Qmake)
+                c = unibyte_char_to_multibyte (*p);
+              else
+                c = BYTE8_TO_CHAR (*p);
 
               bytes = CHAR_STRING (c, tmp);
               *p = tmp[0];
@@ -4979,7 +5026,7 @@ init_buffer ()
   
   Fset_buffer (Fget_buffer_create (build_string ("*scratch*")));
   if (NILP (buffer_defaults.enable_multibyte_characters))
-    Fset_buffer_multibyte (Qnil);
+    Fset_buffer_multibyte (Qnil, Qnil);
 
   /* If PWD is accurate, use it instead of calling getwd.  PWD is
      sometimes a nicer name, and using it may avoid a fatal error if a
@@ -5073,6 +5120,13 @@ syms_of_buffer ()
   Qafter_change_functions = intern ("after-change-functions");
   staticpro (&Qafter_change_functions);
 
+  Qas = intern ("as");
+  staticpro (&Qas);
+  Qmake = intern ("make");
+  staticpro (&Qmake);
+  Qto = intern ("to");
+  staticpro (&Qto);
+
   Fput (Qprotected_field, Qerror_conditions,
         Fcons (Qprotected_field, Fcons (Qerror, Qnil)));
   Fput (Qprotected_field, Qerror_message,