From 15318cad33835e4e2dc620d033e43cd930676cdd Mon Sep 17 00:00:00 2001
From: kergoth <kergoth>
Date: Fri, 25 Jan 2002 22:14:26 +0000
Subject: Initial revision

---
(limited to 'rsync/checksum.c')

diff --git a/rsync/checksum.c b/rsync/checksum.c
new file mode 100644
index 0000000..eab9e46
--- a/dev/null
+++ b/rsync/checksum.c
@@ -0,0 +1,81 @@
+/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
+ *
+ * librsync -- the library for network deltas
+ * $Id$
+ * 
+ * Copyright (C) 1999, 2000, 2001 by Martin Pool <mbp@samba.org>
+ * Copyright (C) 1996 by Andrew Tridgell
+ * Copyright (C) 1996 by Paul Mackerras
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config_rsync.h>
+
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "rsync.h"
+#include "checksum.h"
+
+
+/* This can possibly be used to restart the checksum system in the
+ * case where we detected corruption.  I'm not sure yet how to make
+ * this useful in librsync. */
+int checksum_seed = 0;
+
+/*
+ * A simple 32 bit checksum that can be updated from either end
+ * (inspired by Mark Adler's Adler-32 checksum)
+ */
+unsigned int rs_calc_weak_sum(void const *p, int len)
+{
+        int i;
+        unsigned        s1, s2;
+        unsigned char const    *buf = (unsigned char const *) p;
+
+        s1 = s2 = 0;
+        for (i = 0; i < (len - 4); i += 4) {
+                s2 += 4 * (s1 + buf[i]) + 3 * buf[i + 1] +
+                        2 * buf[i + 2] + buf[i + 3] + 10 * RS_CHAR_OFFSET;
+                s1 += (buf[i + 0] + buf[i + 1] + buf[i + 2] + buf[i + 3] +
+                       4 * RS_CHAR_OFFSET);
+        }
+        for (; i < len; i++) {
+                s1 += (buf[i] + RS_CHAR_OFFSET);
+                s2 += s1;
+        }
+        return (s1 & 0xffff) + (s2 << 16);
+}
+
+
+/**
+ * Calculate and store into SUM a strong MD4 checksum of the file
+ * blocks seen so far.
+ *
+ * In plain rsync, the checksum is perturbed by a seed value.  This is
+ * used when retrying a failed transmission: we've discovered that the
+ * hashes collided at some point, so we're going to try again with
+ * different hashes to see if we can get it right.  (Check tridge's
+ * thesis for details and to see if that's correct.)
+ *
+ * Since we can't retry a web transaction I'm not sure if it's very
+ * useful in rproxy.
+ */
+void rs_calc_strong_sum(void const *buf, size_t len, rs_strong_sum_t *sum)
+{
+    rs_mdfour((unsigned char *) sum, buf, len);
+}
--
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