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Unified Diff: content/common/partial_circular_buffer.cc

Issue 13473005: Adding partially circular memory buffer wrapper. (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: Code review and rebase. Created 7 years, 8 months ago
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Index: content/common/partial_circular_buffer.cc
diff --git a/content/common/partial_circular_buffer.cc b/content/common/partial_circular_buffer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8026fdb1cc585cea92088118f07243e14dd7e47b
--- /dev/null
+++ b/content/common/partial_circular_buffer.cc
@@ -0,0 +1,156 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/common/partial_circular_buffer.h"
+
+#include "base/logging.h"
+
+namespace content {
+
+PartialCircularBuffer::PartialCircularBuffer(void* buffer,
+ uint32 buffer_size)
+ : buffer_data_(reinterpret_cast<BufferData*>(buffer)),
+ memory_buffer_size_(buffer_size),
+ data_size_(0),
+ position_(0),
+ total_read_(0) {
+ uint32 header_size =
+ buffer_data_->data - reinterpret_cast<uint8*>(buffer_data_);
+ data_size_ = memory_buffer_size_ - header_size;
+
+ DCHECK(buffer_data_);
+ DCHECK_GE(memory_buffer_size_, header_size);
+ DCHECK_LE(buffer_data_->total_written, data_size_);
+ DCHECK_LT(buffer_data_->wrap_position, data_size_);
+ DCHECK_LT(buffer_data_->end_position, data_size_);
+}
+
+PartialCircularBuffer::PartialCircularBuffer(void* buffer,
+ uint32 buffer_size,
+ uint32 wrap_position)
+ : buffer_data_(reinterpret_cast<BufferData*>(buffer)),
+ memory_buffer_size_(buffer_size),
+ data_size_(0),
+ position_(0),
+ total_read_(0) {
+ uint32 header_size =
+ buffer_data_->data - reinterpret_cast<uint8*>(buffer_data_);
+ data_size_ = memory_buffer_size_ - header_size;
+
+ DCHECK(buffer_data_);
+ DCHECK_GE(memory_buffer_size_, header_size);
+ DCHECK_LT(wrap_position, data_size_);
+
+ buffer_data_->total_written = 0;
+ buffer_data_->wrap_position = wrap_position;
+ buffer_data_->end_position = 0;
+}
+
+uint32 PartialCircularBuffer::Read(void* buffer, uint32 buffer_size) {
+ DCHECK(buffer_data_);
+ if (total_read_ >= buffer_data_->total_written)
+ return 0;
+
+ uint8* buffer_uint8 = reinterpret_cast<uint8*>(buffer);
+ uint32 read = 0;
+
+ // Read from beginning part.
+ if (position_ < buffer_data_->wrap_position) {
+ uint32 to_wrap_pos = buffer_data_->wrap_position - position_;
+ uint32 to_eow = buffer_data_->total_written - total_read_;
+ uint32 to_read = Min3(buffer_size, to_wrap_pos, to_eow);
+ memcpy(buffer_uint8, buffer_data_->data + position_, to_read);
+ position_ += to_read;
+ total_read_ += to_read;
+ read += to_read;
+ if (position_ == buffer_data_->wrap_position &&
+ buffer_data_->total_written == data_size_) {
+ // We've read all the beginning part, set the position to the middle part.
+ // (The second condition above checks if the wrapping part is filled, i.e.
+ // writing has wrapped.)
+ position_ = buffer_data_->end_position;
+ }
+ if (read >= buffer_size) {
+ DCHECK_EQ(read, buffer_size);
+ return read;
+ }
+ if (read >= to_eow) {
+ DCHECK_EQ(read, to_eow);
+ DCHECK_EQ(total_read_, buffer_data_->total_written);
+ return read;
+ }
+ }
+
+ // Read from middle part.
+ DCHECK_GE(position_, buffer_data_->wrap_position);
+ if (position_ >= buffer_data_->end_position) {
+ uint32 remaining_buffer_size = buffer_size - read;
+ uint32 to_eof = data_size_ - position_;
+ uint32 to_eow = buffer_data_->total_written - total_read_;
+ uint32 to_read = Min3(remaining_buffer_size, to_eof, to_eow);
+ memcpy(buffer_uint8 + read, buffer_data_->data + position_, to_read);
+ position_ += to_read;
+ total_read_ += to_read;
+ read += to_read;
+ if (position_ == data_size_) {
+ // We've read all the middle part, set position to the end part.
+ position_ = buffer_data_->wrap_position;
+ }
+ if (read >= buffer_size) {
+ DCHECK_EQ(read, buffer_size);
+ return read;
+ }
+ if (total_read_ >= buffer_data_->total_written) {
+ DCHECK_EQ(total_read_, buffer_data_->total_written);
+ return read;
+ }
+ }
+
+ // Read from end part.
+ DCHECK_GE(position_, buffer_data_->wrap_position);
+ DCHECK_LT(position_, buffer_data_->end_position);
+ uint32 remaining_buffer_size = buffer_size - read;
+ uint32 to_eob = buffer_data_->end_position - position_;
+ uint32 to_eow = buffer_data_->total_written - total_read_;
+ uint32 to_read = Min3(remaining_buffer_size, to_eob, to_eow);
+ memcpy(buffer_uint8 + read, buffer_data_->data + position_, to_read);
+ position_ += to_read;
+ total_read_ += to_read;
+ read += to_read;
+ DCHECK_LE(read, buffer_size);
+ DCHECK_LE(total_read_, buffer_data_->total_written);
+ return read;
+}
+
+void PartialCircularBuffer::Write(const void* buffer, uint32 buffer_size) {
+ DCHECK(buffer_data_);
+ uint32 position_before_write = position_;
+
+ uint32 to_eof = data_size_ - position_;
+ uint32 to_write = std::min(buffer_size, to_eof);
+ DoWrite(buffer_data_->data + position_, buffer, to_write);
+ if (position_ >= data_size_) {
+ DCHECK_EQ(position_, data_size_);
+ position_ = buffer_data_->wrap_position;
+ }
+
+ if (to_write < buffer_size) {
+ uint32 remainder_to_write = buffer_size - to_write;
+ DCHECK_LT(position_, position_before_write);
+ DCHECK_LE(position_ + remainder_to_write, position_before_write);
+ DoWrite(buffer_data_->data + position_,
+ reinterpret_cast<const uint8*>(buffer) + to_write,
+ remainder_to_write);
+ }
+}
+
+void PartialCircularBuffer::DoWrite(void* dest, const void* src, uint32 num) {
+ memcpy(dest, src, num);
+ position_ += num;
+ buffer_data_->total_written =
+ std::min(buffer_data_->total_written + num, data_size_);
+ buffer_data_->end_position = position_;
+}
+
+} // namespace content

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