Lift the MOST_POSITIVE_FIXNUM/4 limitation on visited files (bug#8528).

 src/fileio.c (Finsert_file_contents): Don't limit file size to 1/4
 of MOST_POSITIVE_FIXNUM.
 src/coding.c (coding_alloc_by_realloc): Error out if destination
 will grow beyond MOST_POSITIVE_FIXNUM.
 (decode_coding_emacs_mule): Abort if there isn't enough place in
 charbuf for the composition carryover bytes.  Reserve an extra
 space for up to 2 characters produced in a loop.
 (decode_coding_iso_2022): Abort if there isn't enough place in
 charbuf for the composition carryover bytes.

1 files changed, 3 insertions, 8 deletions

diff --git a/src/fileio.c b/src/fileio.c
index dcba6b6c0ae..7e6fd8c82a8 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3245,15 +3245,10 @@ variable `last-coding-system-used' to the coding system actually used.  */)
   record_unwind_protect (close_file_unwind, make_number (fd));
 
 
-  /* Arithmetic overflow can occur if an Emacs integer cannot represent the
-     file size, or if the calculations below overflow.  The calculations below
-     double the file size twice, so check that it can be multiplied by 4
-     safely.
-
-     Also check whether the size is negative, which can happen on a platform
-     that allows file sizes greater than the maximum off_t value.  */
+  /* Check whether the size is too large or negative, which can happen on a
+     platform that allows file sizes greater than the maximum off_t value.  */
   if (! not_regular
-      && ! (0 <= st.st_size && st.st_size <= MOST_POSITIVE_FIXNUM / 4))
+      && ! (0 <= st.st_size && st.st_size <= MOST_POSITIVE_FIXNUM))
     error ("Maximum buffer size exceeded");
 
   /* Prevent redisplay optimizations.  */