* lib/xalloc.h (x2nrealloc): Fix an unlikely bug in the overflow

checking code.  Set N = ceil (1.5 * N) rather than to a slightly
larger value.

        Give tools a better chance to allocate space for very large buffers.
* lib/xalloc.h (x2nrealloc): Use 3/2, not 2, as buffer size factor.

diff --git a/ChangeLog b/ChangeLog
index 7b35b21..dc7195b 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
+2007-02-03  Paul Eggert  <eggert@cs.ucla.edu>
+
+       * lib/xalloc.h (x2nrealloc): Fix an unlikely bug in the overflow
+       checking code.  Set N = ceil (1.5 * N) rather than to a slightly
+       larger value.
+
 2007-02-03  Jim Meyering  <jim@meyering.net>
 
+        Give tools a better chance to allocate space for very large buffers.
+       * lib/xalloc.h (x2nrealloc): Use 3/2, not 2, as buffer size factor.
+
        Make pwd and readlink work also when run with an unreadable parent dir
        on systems with openat support.
        * lib/getcwd.c (__getcwd) [HAVE_PARTLY_WORKING_GETCWD]: Use the system

diff --git a/lib/xalloc.h b/lib/xalloc.h
index fb5cdca..0c6d8dc 100644 (file)
--- a/lib/xalloc.h
+++ b/lib/xalloc.h
@@ -141,7 +141,7 @@ xnrealloc (void *p, size_t n, size_t s)
 
    In the following implementation, nonzero sizes are increased by a
    factor of approximately 1.5 so that repeated reallocations have
-   O(N log N) overall cost rather than O(N**2) cost, but the
+   O(N) overall cost rather than O(N**2) cost, but the
    specification for this function does not guarantee that rate.
 
    Here is an example of use:
@@ -204,9 +204,13 @@ x2nrealloc (void *p, size_t *pn, size_t s)
     }
   else
     {
-      if ((2 * (((size_t) -1 - 1) / 3)) / s < n)
+      /* Set N = ceil (1.5 * N) so that progress is made if N == 1.
+        Check for overflow, so that N * S stays in size_t range.
+        The check is slightly conservative, but an exact check isn't
+        worth the trouble.  */
+      if ((size_t) -1 / 3 * 2 / s <= n)
        xalloc_die ();
-      n = n + n / 2 + 1;
+      n += (n + 1) / 2;
     }
 
   *pn = n;