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diff --git a/subversion/libsvn_subr/adler32.c b/subversion/libsvn_subr/adler32.c
new file mode 100644
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+++ b/subversion/libsvn_subr/adler32.c
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+/*
+ * adler32.c :  routines for handling Adler-32 checksums
+ *
+ * ====================================================================
+ *    Licensed to the Apache Software Foundation (ASF) under one
+ *    or more contributor license agreements.  See the NOTICE file
+ *    distributed with this work for additional information
+ *    regarding copyright ownership.  The ASF licenses this file
+ *    to you under the Apache License, Version 2.0 (the
+ *    "License"); you may not use this file except in compliance
+ *    with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing,
+ *    software distributed under the License is distributed on an
+ *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *    KIND, either express or implied.  See the License for the
+ *    specific language governing permissions and limitations
+ *    under the License.
+ * ====================================================================
+ */
+
+
+#include <apr.h>
+#include <zlib.h>
+
+#include "private/svn_adler32.h"
+
+/**
+ * An Adler-32 implementation per RFC1950.
+ *
+ * "The Adler-32 algorithm is much faster than the CRC32 algorithm yet
+ * still provides an extremely low probability of undetected errors"
+ */
+
+/*
+ * 65521 is the largest prime less than 65536.
+ * "That 65521 is prime is important to avoid a possible large class of
+ *  two-byte errors that leave the check unchanged."
+ */
+#define ADLER_MOD_BASE 65521
+
+/*
+ * Start with CHECKSUM and update the checksum by processing a chunk
+ * of DATA sized LEN.
+ */
+apr_uint32_t
+svn__adler32(apr_uint32_t checksum, const char *data, apr_off_t len)
+{
+  /* The actual limit can be set somewhat higher but should
+   * not be lower because the SIMD code would not be used
+   * in that case.
+   *
+   * However, it must be lower than 5552 to make sure our local
+   * implementation does not suffer from overflows.
+   */
+  if (len >= 80)
+    {
+      /* Larger buffers can be effiently handled by Marc Adler's
+       * optimized code. Also, new zlib versions will come with
+       * SIMD code for x86 and x64.
+       */
+      return (apr_uint32_t)adler32(checksum,
+                                   (const Bytef *)data,
+                                   (uInt)len);
+    }
+  else
+    {
+      const unsigned char *input = (const unsigned char *)data;
+      apr_uint32_t s1 = checksum & 0xFFFF;
+      apr_uint32_t s2 = checksum >> 16;
+      apr_uint32_t b;
+
+      /* Some loop unrolling
+       * (approx. one clock tick per byte + 2 ticks loop overhead)
+       */
+      for (; len >= 8; len -= 8, input += 8)
+      {
+        s1 += input[0]; s2 += s1;
+        s1 += input[1]; s2 += s1;
+        s1 += input[2]; s2 += s1;
+        s1 += input[3]; s2 += s1;
+        s1 += input[4]; s2 += s1;
+        s1 += input[5]; s2 += s1;
+        s1 += input[6]; s2 += s1;
+        s1 += input[7]; s2 += s1;
+      }
+
+      /* Adler-32 calculation as a simple two ticks per iteration loop.
+       */
+      while (len--)
+        {
+          b = *input++;
+          s1 += b;
+          s2 += s1;
+        }
+
+      return ((s2 % ADLER_MOD_BASE) << 16) | (s1 % ADLER_MOD_BASE);
+    }
+}