diff -burpN -x CVS -x 'cscope*' -x Makefile.in -x configure -x autom4te.cache -x aclocal.m4 coreutils/ChangeLog coreutils.lcm/ChangeLog
--- coreutils/ChangeLog	2005-11-18 16:24:52.000000000 -0600
+++ coreutils.lcm/ChangeLog	2005-11-18 16:24:34.000000000 -0600
@@ -1,3 +1,10 @@
+2005-11-18  Rob Latham <address@hidden>
+	* lib/Makefile.am, lib/buffer-lcm.c, lib/buffer-lcm.h: add code to find
+	  least common multiple of two values, with logic to handle unusual
+	  input (taken from diffutils)
+	* src/copy.c: use the LCM of the source and dest blocksize when
+	  figuring out the ideal blocksize.
+
 2005-11-17  Jim Meyering  <address@hidden>
 
 	* Version 6.0-cvs.
diff -burpN -x CVS -x 'cscope*' -x Makefile.in -x configure -x autom4te.cache -x aclocal.m4 coreutils/lib/buffer-lcm.c coreutils.lcm/lib/buffer-lcm.c
--- coreutils/lib/buffer-lcm.c	1969-12-31 18:00:00.000000000 -0600
+++ coreutils.lcm/lib/buffer-lcm.c	2005-11-18 10:04:54.000000000 -0600
@@ -0,0 +1,47 @@
+/* buffer-lcm.c - an lcm routine used for computing optimal buffer size
+ 
+   Copyright (C) 2005 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+
+/* Least common multiple of two buffer sizes A and B.  However, if
+   either A or B is zero, or if the multiple is greater than LCM_MAX,
+   return a reasonable buffer size.  
+ 
+   This method was taken from diffutils/lib/cmpbuf.c */
+
+#include <sys/types.h>
+
+size_t
+buffer_lcm (size_t a, size_t b, size_t lcm_max)
+{
+  size_t lcm, m, n, q, r;
+
+  /* Yield reasonable values if buffer sizes are zero.  */
+  if (!a)
+    return b ? b : 8 * 1024;
+  if (!b)
+    return a;
+
+  /* n = gcd (a, b) */
+  for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)
+    continue;
+
+  /* Yield a if there is an overflow.  */
+  q = a / n;
+  lcm = q * b;
+  return lcm <= lcm_max && lcm / b == q ? lcm : a;
+}
diff -burpN -x CVS -x 'cscope*' -x Makefile.in -x configure -x autom4te.cache -x aclocal.m4 coreutils/lib/buffer-lcm.h coreutils.lcm/lib/buffer-lcm.h
--- coreutils/lib/buffer-lcm.h	1969-12-31 18:00:00.000000000 -0600
+++ coreutils.lcm/lib/buffer-lcm.h	2005-11-18 10:04:54.000000000 -0600
@@ -0,0 +1,23 @@
+/* buffer-lcm.c - an lcm routine used for computing optimal buffer size
+
+   Copyright (C) 2005 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Taken from diffutils/lib/cmpbuf.c */
+
+#include <sys/types.h>
+
+size_t buffer_lcm(size_t a, size_t b, size_t lcm_max);
diff -burpN -x CVS -x 'cscope*' -x Makefile.in -x configure -x autom4te.cache -x aclocal.m4 coreutils/lib/Makefile.am coreutils.lcm/lib/Makefile.am
--- coreutils/lib/Makefile.am	2005-10-05 09:54:17.000000000 -0500
+++ coreutils.lcm/lib/Makefile.am	2005-11-18 10:04:54.000000000 -0600
@@ -27,6 +27,7 @@ DEFS += -DLIBDIR=\"$(libdir)\"
 
 libcoreutils_a_SOURCES = \
   allocsa.c allocsa.h \
+  buffer-lcm.c buffer-lcm.h \
   euidaccess.h \
   exit.h \
   fprintftime.c fprintftime.h \
diff -burpN -x CVS -x 'cscope*' -x Makefile.in -x configure -x autom4te.cache -x aclocal.m4 coreutils/src/copy.c coreutils.lcm/src/copy.c
--- coreutils/src/copy.c	2005-09-24 22:07:33.000000000 -0500
+++ coreutils.lcm/src/copy.c	2005-11-18 10:04:54.000000000 -0600
@@ -31,6 +31,7 @@
 
 #include "system.h"
 #include "backupfile.h"
+#include "buffer-lcm.h"
 #include "copy.h"
 #include "cp-hash.h"
 #include "dirname.h"
@@ -291,7 +292,7 @@ copy_reg (char const *src_name, char con
       goto close_src_and_dst_desc;
     }
 
-  buf_size = ST_BLKSIZE (sb);
+  buf_size = buffer_lcm(ST_BLKSIZE (sb), ST_BLKSIZE(src_open_sb), SIZE_MAX);
 
   /* Even with --sparse=always, try to create holes only
      if the destination is a regular file.  */