Squashed 'gitstatus/' content from commit 6b9ba17

git-subtree-dir: gitstatus
git-subtree-split: 6b9ba179c6655286c4c399e7926d5098dd6bd706

src/arena.cc

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+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "arena.h"
+
+#include <algorithm>
+#include <type_traits>
+
+#include "bits.h"
+#include "check.h"
+
+namespace gitstatus {
+
+namespace {
+
+size_t Clamp(size_t min, size_t val, size_t max) { return std::min(max, std::max(min, val)); }
+
+static const uintptr_t kSingularity = reinterpret_cast<uintptr_t>(&kSingularity);
+
+}  // namespace
+
+// Triple singularity. We are all fucked.
+Arena::Block Arena::g_empty_block = {kSingularity, kSingularity, kSingularity};
+
+Arena::Arena(Arena::Options opt) : opt_(std::move(opt)), top_(&g_empty_block) {
+  CHECK(opt_.min_block_size <= opt_.max_block_size);
+}
+
+Arena::Arena(Arena&& other) : Arena() { *this = std::move(other); }
+
+Arena::~Arena() {
+  // See comments in Makefile for the reason sized deallocation is not used.
+  for (const Block& b : blocks_) ::operator delete(reinterpret_cast<void*>(b.start));
+}
+
+Arena& Arena::operator=(Arena&& other) {
+  if (this != &other) {
+    // In case std::vector ever gets small object optimization.
+    size_t idx = other.reusable_ ? other.top_ - other.blocks_.data() : 0;
+    opt_ = other.opt_;
+    blocks_ = std::move(other.blocks_);
+    reusable_ = other.reusable_;
+    top_ = reusable_ ? blocks_.data() + idx : &g_empty_block;
+    other.blocks_.clear();
+    other.reusable_ = 0;
+    other.top_ = &g_empty_block;
+  }
+  return *this;
+}
+
+void Arena::Reuse(size_t num_blocks) {
+  reusable_ = std::min(reusable_, num_blocks);
+  for (size_t i = reusable_; i != blocks_.size(); ++i) {
+    const Block& b = blocks_[i];
+    // See comments in Makefile for the reason sized deallocation is not used.
+    ::operator delete(reinterpret_cast<void*>(b.start));
+  }
+  blocks_.resize(reusable_);
+  if (reusable_) {
+    top_ = blocks_.data();
+    top_->tip = top_->start;
+  } else {
+    top_ = &g_empty_block;
+  }
+}
+
+void Arena::AddBlock(size_t size, size_t alignment) {
+  if (alignment > alignof(std::max_align_t)) {
+    size += alignment - 1;
+  } else {
+    size = std::max(size, alignment);
+  }
+  if (size <= top_->size() && top_ < blocks_.data() + reusable_ - 1) {
+    assert(blocks_.front().size() == top_->size());
+    ++top_;
+    top_->tip = top_->start;
+    return;
+  }
+  if (size <= opt_.max_alloc_threshold) {
+    size =
+        std::max(size, Clamp(opt_.min_block_size, NextPow2(top_->size() + 1), opt_.max_block_size));
+  }
+
+  auto p = reinterpret_cast<uintptr_t>(::operator new(size));
+  blocks_.push_back(Block{p, p, p + size});
+  if (reusable_) {
+    if (size < blocks_.front().size()) {
+      top_ = &blocks_.back();
+      return;
+    }
+    if (size > blocks_.front().size()) reusable_ = 0;
+  }
+  std::swap(blocks_.back(), blocks_[reusable_]);
+  top_ = &blocks_[reusable_++];
+}
+
+void* Arena::AllocateSlow(size_t size, size_t alignment) {
+  assert(alignment && !(alignment & (alignment - 1)));
+  AddBlock(size, alignment);
+  assert(Align(top_->tip, alignment) + size <= top_->end);
+  return Allocate(size, alignment);
+}
+
+}  // namespace gitstatus