1 files changed, 216 insertions, 0 deletions
diff --git a/src/rocksdb/util/comparator.cc b/src/rocksdb/util/comparator.cc
new file mode 100644
index 000000000..48340bd96
--- /dev/null
+++ b/src/rocksdb/util/comparator.cc
@@ -0,0 +1,216 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#include "rocksdb/comparator.h"
+#include <stdint.h>
+#include <algorithm>
+#include <memory>
+#include "logging/logging.h"
+#include "port/port.h"
+#include "rocksdb/slice.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+namespace {
+class BytewiseComparatorImpl : public Comparator {
+ public:
+  BytewiseComparatorImpl() { }
+
+  const char* Name() const override { return "leveldb.BytewiseComparator"; }
+
+  int Compare(const Slice& a, const Slice& b) const override {
+    return a.compare(b);
+  }
+
+  bool Equal(const Slice& a, const Slice& b) const override { return a == b; }
+
+  void FindShortestSeparator(std::string* start,
+                             const Slice& limit) const override {
+    // Find length of common prefix
+    size_t min_length = std::min(start->size(), limit.size());
+    size_t diff_index = 0;
+    while ((diff_index < min_length) &&
+           ((*start)[diff_index] == limit[diff_index])) {
+      diff_index++;
+    }
+
+    if (diff_index >= min_length) {
+      // Do not shorten if one string is a prefix of the other
+    } else {
+      uint8_t start_byte = static_cast<uint8_t>((*start)[diff_index]);
+      uint8_t limit_byte = static_cast<uint8_t>(limit[diff_index]);
+      if (start_byte >= limit_byte) {
+        // Cannot shorten since limit is smaller than start or start is
+        // already the shortest possible.
+        return;
+      }
+      assert(start_byte < limit_byte);
+
+      if (diff_index < limit.size() - 1 || start_byte + 1 < limit_byte) {
+        (*start)[diff_index]++;
+        start->resize(diff_index + 1);
+      } else {
+        //     v
+        // A A 1 A A A
+        // A A 2
+        //
+        // Incrementing the current byte will make start bigger than limit, we
+        // will skip this byte, and find the first non 0xFF byte in start and
+        // increment it.
+        diff_index++;
+
+        while (diff_index < start->size()) {
+          // Keep moving until we find the first non 0xFF byte to
+          // increment it
+          if (static_cast<uint8_t>((*start)[diff_index]) <
+              static_cast<uint8_t>(0xff)) {
+            (*start)[diff_index]++;
+            start->resize(diff_index + 1);
+            break;
+          }
+          diff_index++;
+        }
+      }
+      assert(Compare(*start, limit) < 0);
+    }
+  }
+
+  void FindShortSuccessor(std::string* key) const override {
+    // Find first character that can be incremented
+    size_t n = key->size();
+    for (size_t i = 0; i < n; i++) {
+      const uint8_t byte = (*key)[i];
+      if (byte != static_cast<uint8_t>(0xff)) {
+        (*key)[i] = byte + 1;
+        key->resize(i+1);
+        return;
+      }
+    }
+    // *key is a run of 0xffs.  Leave it alone.
+  }
+
+  bool IsSameLengthImmediateSuccessor(const Slice& s,
+                                      const Slice& t) const override {
+    if (s.size() != t.size() || s.size() == 0) {
+      return false;
+    }
+    size_t diff_ind = s.difference_offset(t);
+    // same slice
+    if (diff_ind >= s.size()) return false;
+    uint8_t byte_s = static_cast<uint8_t>(s[diff_ind]);
+    uint8_t byte_t = static_cast<uint8_t>(t[diff_ind]);
+    // first different byte must be consecutive, and remaining bytes must be
+    // 0xff for s and 0x00 for t
+    if (byte_s != uint8_t{0xff} && byte_s + 1 == byte_t) {
+      for (size_t i = diff_ind + 1; i < s.size(); ++i) {
+        byte_s = static_cast<uint8_t>(s[i]);
+        byte_t = static_cast<uint8_t>(t[i]);
+        if (byte_s != uint8_t{0xff} || byte_t != uint8_t{0x00}) {
+          return false;
+        }
+      }
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  bool CanKeysWithDifferentByteContentsBeEqual() const override {
+    return false;
+  }
+
+  int CompareWithoutTimestamp(const Slice& a, const Slice& b) const override {
+    return a.compare(b);
+  }
+};
+
+class ReverseBytewiseComparatorImpl : public BytewiseComparatorImpl {
+ public:
+  ReverseBytewiseComparatorImpl() { }
+
+  const char* Name() const override {
+    return "rocksdb.ReverseBytewiseComparator";
+  }
+
+  int Compare(const Slice& a, const Slice& b) const override {
+    return -a.compare(b);
+  }
+
+  void FindShortestSeparator(std::string* start,
+                             const Slice& limit) const override {
+    // Find length of common prefix
+    size_t min_length = std::min(start->size(), limit.size());
+    size_t diff_index = 0;
+    while ((diff_index < min_length) &&
+           ((*start)[diff_index] == limit[diff_index])) {
+      diff_index++;
+    }
+
+    assert(diff_index <= min_length);
+    if (diff_index == min_length) {
+      // Do not shorten if one string is a prefix of the other
+      //
+      // We could handle cases like:
+      //     V
+      // A A 2 X Y
+      // A A 2
+      // in a similar way as BytewiseComparator::FindShortestSeparator().
+      // We keep it simple by not implementing it. We can come back to it
+      // later when needed.
+    } else {
+      uint8_t start_byte = static_cast<uint8_t>((*start)[diff_index]);
+      uint8_t limit_byte = static_cast<uint8_t>(limit[diff_index]);
+      if (start_byte > limit_byte && diff_index < start->size() - 1) {
+        // Case like
+        //     V
+        // A A 3 A A
+        // A A 1 B B
+        //
+        // or
+        //     v
+        // A A 2 A A
+        // A A 1 B B
+        // In this case "AA2" will be good.
+#ifndef NDEBUG
+        std::string old_start = *start;
+#endif
+        start->resize(diff_index + 1);
+#ifndef NDEBUG
+        assert(old_start >= *start);
+#endif
+        assert(Slice(*start).compare(limit) > 0);
+      }
+    }
+  }
+
+  void FindShortSuccessor(std::string* /*key*/) const override {
+    // Don't do anything for simplicity.
+  }
+
+  bool CanKeysWithDifferentByteContentsBeEqual() const override {
+    return false;
+  }
+
+  int CompareWithoutTimestamp(const Slice& a, const Slice& b) const override {
+    return -a.compare(b);
+  }
+};
+}// namespace
+
+const Comparator* BytewiseComparator() {
+  static BytewiseComparatorImpl bytewise;
+  return &bytewise;
+}
+
+const Comparator* ReverseBytewiseComparator() {
+  static ReverseBytewiseComparatorImpl rbytewise;
+  return &rbytewise;
+}
+
+}  // namespace ROCKSDB_NAMESPACE