(readchar): Use readchar_backlog again

to read a character byte by byte, if its byte sequence
does not really match the character code.
(unreadchar): Handle readchar_backlog.
(readevalloop, Fread): Initialize readchar_backlog to -1.

1 files changed, 87 insertions, 13 deletions

diff --git a/src/lread.c b/src/lread.c
index 00d93192f30..3eb56a2c35a 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -183,14 +183,46 @@ readchar (readcharfun)
       int pt_byte = BUF_PT_BYTE (inbuffer);
       int orig_pt_byte = pt_byte;
 
+      if (readchar_backlog > 0)
+        /* We get the address of the byte just passed,
+           which is the last byte of the character.
+           The other bytes in this character are consecutive with it,
+           because the gap can't be in the middle of a character.  */
+        return *(BUF_BYTE_ADDRESS (inbuffer, BUF_PT_BYTE (inbuffer) - 1)
+                 - --readchar_backlog);
+
       if (pt_byte >= BUF_ZV_BYTE (inbuffer))
         return -1;
 
+      readchar_backlog = -1;
+
       if (! NILP (inbuffer->enable_multibyte_characters))
         {
+          unsigned char workbuf[4];
+          unsigned char *str = workbuf;
+          int length;
+
+          /* Fetch the character code from the buffer.  */
           unsigned char *p = BUF_BYTE_ADDRESS (inbuffer, pt_byte);
           BUF_INC_POS (inbuffer, pt_byte);
           c = STRING_CHAR (p, pt_byte - orig_pt_byte);
+
+          /* Find the byte-sequence representation of that character.  */
+          if (SINGLE_BYTE_CHAR_P (c))
+            length = 1, workbuf[0] = c;
+          else
+            length = non_ascii_char_to_string (c, workbuf, &str);
+
+          /* If the bytes for this character in the buffer
+             are not identical with what the character code implies,
+             read the bytes one by one from the buffer.  */
+          if (length != pt_byte - orig_pt_byte
+              || (length == 1 ? *str != *p : bcmp (str, p, length)))
+            {
+              readchar_backlog = pt_byte - orig_pt_byte;
+              c = BUF_FETCH_BYTE (inbuffer, orig_pt_byte);
+              readchar_backlog--;
+            }
         }
       else
         {
@@ -208,14 +240,46 @@ readchar (readcharfun)
       int bytepos = marker_byte_position (readcharfun);
       int orig_bytepos = bytepos;
 
+      if (readchar_backlog > 0)
+        /* We get the address of the byte just passed,
+           which is the last byte of the character.
+           The other bytes in this character are consecutive with it,
+           because the gap can't be in the middle of a character.  */
+        return *(BUF_BYTE_ADDRESS (inbuffer, XMARKER (readcharfun)->bytepos - 1)
+                 - --readchar_backlog);
+
       if (bytepos >= BUF_ZV_BYTE (inbuffer))
         return -1;
 
+      readchar_backlog = -1;
+
       if (! NILP (inbuffer->enable_multibyte_characters))
         {
+          unsigned char workbuf[4];
+          unsigned char *str = workbuf;
+          int length;
+
+          /* Fetch the character code from the buffer.  */
           unsigned char *p = BUF_BYTE_ADDRESS (inbuffer, bytepos);
           BUF_INC_POS (inbuffer, bytepos);
           c = STRING_CHAR (p, bytepos - orig_bytepos);
+
+          /* Find the byte-sequence representation of that character.  */
+          if (SINGLE_BYTE_CHAR_P (c))
+            length = 1, workbuf[0] = c;
+          else
+            length = non_ascii_char_to_string (c, workbuf, &str);
+
+          /* If the bytes for this character in the buffer
+             are not identical with what the character code implies,
+             read the bytes one by one from the buffer.  */
+          if (length != bytepos - orig_bytepos
+              || (length == 1 ? *str != *p : bcmp (str, p, length)))
+            {
+              readchar_backlog = bytepos - orig_bytepos;
+              c = BUF_FETCH_BYTE (inbuffer, orig_bytepos);
+              readchar_backlog--;
+            }
         }
       else
         {
@@ -280,26 +344,36 @@ unreadchar (readcharfun, c)
       struct buffer *b = XBUFFER (readcharfun);
       int bytepos = BUF_PT_BYTE (b);
 
-      BUF_PT (b)--;
-      if (! NILP (b->enable_multibyte_characters))
-        BUF_DEC_POS (b, bytepos);
+      if (readchar_backlog >= 0)
+        readchar_backlog++;
       else
-        bytepos--;
+        {
+          BUF_PT (b)--;
+          if (! NILP (b->enable_multibyte_characters))
+            BUF_DEC_POS (b, bytepos);
+          else
+            bytepos--;
 
-      BUF_PT_BYTE (b) = bytepos;
+          BUF_PT_BYTE (b) = bytepos;
+        }
     }
   else if (MARKERP (readcharfun))
     {
       struct buffer *b = XMARKER (readcharfun)->buffer;
       int bytepos = XMARKER (readcharfun)->bytepos;
 
-      XMARKER (readcharfun)->charpos--;
-      if (! NILP (b->enable_multibyte_characters))
-        BUF_DEC_POS (b, bytepos);
+      if (readchar_backlog >= 0)
+        readchar_backlog++;
       else
-        bytepos--;
+        {
+          XMARKER (readcharfun)->charpos--;
+          if (! NILP (b->enable_multibyte_characters))
+            BUF_DEC_POS (b, bytepos);
+          else
+            bytepos--;
 
-      XMARKER (readcharfun)->bytepos = bytepos;
+          XMARKER (readcharfun)->bytepos = bytepos;
+        }
     }
   else if (STRINGP (readcharfun))
     {
@@ -959,7 +1033,7 @@ readevalloop (readcharfun, stream, sourcename, evalfun, printflag, unibyte)
   record_unwind_protect (readevalloop_1, load_convert_to_unibyte ? Qt : Qnil);
   load_convert_to_unibyte = !NILP (unibyte);
 
-  readchar_backlog = 0;
+  readchar_backlog = -1;
 
   GCPRO1 (sourcename);
 
@@ -1147,7 +1221,7 @@ STREAM or the value of `standard-input' may be:\n\
   if (EQ (stream, Qt))
     stream = Qread_char;
 
-  readchar_backlog = 0;
+  readchar_backlog = -1;
   new_backquote_flag = 0;
   read_objects = Qnil;
 
@@ -1726,7 +1800,7 @@ read1 (readcharfun, pch, first_in_list)
         return make_number (c);
       }
 
-    case '\"':
+    case '"':
       {
         register char *p = read_buffer;
         register char *end = read_buffer + read_buffer_size;