1 files changed, 59 insertions, 0 deletions
diff --git a/lib/buffer-lcm.c b/lib/buffer-lcm.c
new file mode 100644
index 0000000..3439864
--- /dev/null
+++ b/lib/buffer-lcm.c
@@ -0,0 +1,59 @@
+/* buffer-lcm.c - compute a good buffer size for dealing with two files
+
+   Copyright (C) 2002-2020 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 3 of the License, 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, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+#include "buffer-lcm.h"
+
+/* Return a buffer size suitable for doing I/O with files whose block
+   sizes are A and B.  However, never return a value greater than
+   LCM_MAX.  */
+
+size_t
+buffer_lcm (size_t a, size_t b, size_t lcm_max)
+{
+  size_t size;
+
+  /* Use reasonable values if buffer sizes are zero.  */
+  if (!a)
+    size = b ? b : 8 * 1024;
+  else
+    {
+      if (b)
+        {
+          /* Return lcm (A, B) if it is in range; otherwise, fall back
+             on A.  */
+
+          size_t lcm, m, n, q, r;
+
+          /* N = gcd (A, B).  */
+          for (m = a, n = b;  (r = m % n) != 0;  m = n, n = r)
+            continue;
+
+          /* LCM = lcm (A, B), if in range.  */
+          q = a / n;
+          lcm = q * b;
+          if (lcm <= lcm_max && lcm / b == q)
+            return lcm;
+        }
+
+      size = a;
+    }
+
+  return size <= lcm_max ? size : lcm_max;
+}