1 files changed, 68 insertions, 0 deletions
diff --git a/util/arena.cc b/util/arena.cc
new file mode 100644
index 0000000..4bf6e36
--- /dev/null
+++ b/util/arena.cc
@@ -0,0 +1,68 @@
+// 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 "util/arena.h"
+#include <assert.h>
+
+namespace leveldb {
+
+static const int kBlockSize = 4096;
+
+Arena::Arena() {
+  blocks_memory_ = 0;
+  alloc_ptr_ = NULL;  // First allocation will allocate a block
+  alloc_bytes_remaining_ = 0;
+}
+
+Arena::~Arena() {
+  for (int i = 0; i < blocks_.size(); i++) {
+    delete[] blocks_[i];
+  }
+}
+
+char* Arena::AllocateFallback(size_t bytes) {
+  if (bytes > kBlockSize / 4) {
+    // Object is more than a quarter of our block size.  Allocate it separately
+    // to avoid wasting too much space in leftover bytes.
+    char* result = AllocateNewBlock(bytes);
+    return result;
+  }
+
+  // We waste the remaining space in the current block.
+  alloc_ptr_ = AllocateNewBlock(kBlockSize);
+  alloc_bytes_remaining_ = kBlockSize;
+
+  char* result = alloc_ptr_;
+  alloc_ptr_ += bytes;
+  alloc_bytes_remaining_ -= bytes;
+  return result;
+}
+
+char* Arena::AllocateAligned(size_t bytes) {
+  const int align = sizeof(void*);    // We'll align to pointer size
+  assert((align & (align-1)) == 0);   // Pointer size should be a power of 2
+  size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1);
+  size_t slop = (current_mod == 0 ? 0 : align - current_mod);
+  size_t needed = bytes + slop;
+  char* result;
+  if (needed <= alloc_bytes_remaining_) {
+    result = alloc_ptr_ + slop;
+    alloc_ptr_ += needed;
+    alloc_bytes_remaining_ -= needed;
+  } else {
+    // AllocateFallback always returned aligned memory
+    result = AllocateFallback(bytes);
+  }
+  assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0);
+  return result;
+}
+
+char* Arena::AllocateNewBlock(size_t block_bytes) {
+  char* result = new char[block_bytes];
+  blocks_memory_ += block_bytes;
+  blocks_.push_back(result);
+  return result;
+}
+
+}