From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sun, 4 Feb 2007 02:20:40 +0000 (+0000)
Subject: * lib/xalloc.h (x2nrealloc): Fix an unlikely bug in the overflow
X-Git-Tag: cvs-readonly~1141
X-Git-Url: http://erislabs.org.uk/gitweb/?a=commitdiff_plain;h=9d7a0ecef081c6ff4233d7bd5fd4c38ab3939d52;p=gnulib.git

* 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 7b35b2103..dc7195b28 100644
--- 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 fb5cdcab3..0c6d8dcf5 100644
--- 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;