Threadsafe bitmap class

src/xenia/base/bit_map.cc

@@ -0,0 +1,96 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2015 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#include "xenia/base/bit_map.h"
+
+#include "xenia/base/assert.h"
+#include "xenia/base/atomic.h"
+#include "xenia/base/math.h"
+
+namespace xe {
+
+BitMap::BitMap() = default;
+
+BitMap::BitMap(size_t size) { Resize(size); }
+
+BitMap::BitMap(uint32_t* data, size_t size) {
+  assert_true(size % 4 == 0);
+
+  data_.resize(size / 4);
+  std::memcpy(data_.data(), data, size);
+}
+
+size_t BitMap::Acquire() {
+  for (size_t i = 0; i < data_.size(); i++) {
+    uint32_t entry = 0;
+    uint32_t new_entry = 0;
+    int acquired_idx = -1;
+
+    do {
+      entry = data_[i];
+      uint8_t index = lzcnt(entry);
+      if (index == kDataSizeBits) {
+        // None free.
+        acquired_idx = -1;
+        break;
+      }
+
+      // Entry has a free bit. Acquire it.
+      uint32_t bit = 1 << (kDataSizeBits - index - 1);
+      new_entry = entry & ~bit;
+      assert_not_zero(entry & bit);
+
+      acquired_idx = index;
+    } while (!atomic_cas(entry, new_entry, &data_[i]));
+
+    if (acquired_idx != -1) {
+      // Acquired.
+      return (i * kDataSizeBits) + acquired_idx;
+    }
+  }
+
+  return -1;
+}
+
+void BitMap::Release(size_t index) {
+  auto slot = index / kDataSizeBits;
+  index -= slot * kDataSizeBits;
+
+  uint32_t bit = 1 << (kDataSizeBits - index - 1);
+
+  uint32_t entry = 0;
+  uint32_t new_entry = 0;
+  do {
+    entry = data_[slot];
+    assert_zero(entry & bit);
+
+    new_entry = entry | bit;
+  } while (!atomic_cas(entry, new_entry, &data_[slot]));
+}
+
+void BitMap::Resize(size_t new_size) {
+  auto old_size = data_.size();
+  assert_true(new_size % 4 == 0);
+  data_.resize(new_size / 4);
+
+  // Initialize new entries.
+  if (data_.size() > old_size) {
+    for (size_t i = old_size; i < data_.size(); i++) {
+      data_[i] = -1;
+    }
+  }
+}
+
+void BitMap::Reset() {
+  for (size_t i = 0; i < data_.size(); i++) {
+    data_[i] = -1;
+  }
+}
+
+}  // namespace xe

src/xenia/base/bit_map.h

@@ -0,0 +1,56 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2015 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_BASE_BIT_MAP_H_
+#define XENIA_BASE_BIT_MAP_H_
+
+#include <cstdint>
+#include <vector>
+
+namespace xe {
+
+// Bit Map: Efficient lookup of free/used entries.
+class BitMap {
+ public:
+  BitMap();
+
+  // Size is the number of 8-bit entries, must be a multiple of 4.
+  BitMap(size_t size);
+
+  // Data does not have to be aligned to a 4-byte boundary, but it is
+  // preferable.
+  // Size is the number of 8-bit entries, must be a multiple of 4.
+  BitMap(uint32_t* data, size_t size);
+
+  // (threadsafe) Acquires an entry and returns its index. Returns -1 if there
+  // are no more free entries.
+  size_t Acquire();
+
+  // (threadsafe) Releases an entry by an index.
+  void Release(size_t index);
+
+  // Resize the bitmap. Size is the number of 8-bit entries, must be a multiple
+  // of 4.
+  void Resize(size_t new_size);
+
+  // Sets all entries to free.
+  void Reset();
+
+  const std::vector<uint32_t> data() const { return data_; }
+  std::vector<uint32_t>& data() { return data_; }
+
+ private:
+  const static uint32_t kDataSize = 4;
+  const static uint32_t kDataSizeBits = kDataSize * 8;
+  std::vector<uint32_t> data_;
+};
+
+}  // namespace xe
+
+#endif  // XENIA_BASE_BIT_MAP_H_