root/net/quic/quic_data_writer.cc

DEFINITIONS

1. length_
2. take
3. WriteUInt8
4. WriteUInt16
5. WriteUInt32
6. WriteUInt48
7. WriteUInt64
8. WriteUFloat16
9. WriteStringPiece16
10. WriteIOVector
11. BeginWrite
12. WriteBytes
13. WriteRepeatedByte
14. WritePadding
15. WriteUInt8ToOffset
16. WriteUInt32ToOffset
17. WriteUInt48ToOffset

// Copyright (c) 2012 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 "net/quic/quic_data_writer.h"

#include <algorithm>
#include <limits>
#include <string>

#include "base/basictypes.h"
#include "base/logging.h"

using base::StringPiece;
using std::numeric_limits;

namespace net {

QuicDataWriter::QuicDataWriter(size_t size)
    : buffer_(new char[size]),
      capacity_(size),
      length_(0) {
}

QuicDataWriter::~QuicDataWriter() {
  delete[] buffer_;
}

char* QuicDataWriter::take() {
  char* rv = buffer_;
  buffer_ = NULL;
  capacity_ = 0;
  length_ = 0;
  return rv;
}

bool QuicDataWriter::WriteUInt8(uint8 value) {
  return WriteBytes(&value, sizeof(value));
}

bool QuicDataWriter::WriteUInt16(uint16 value) {
  return WriteBytes(&value, sizeof(value));
}

bool QuicDataWriter::WriteUInt32(uint32 value) {
  return WriteBytes(&value, sizeof(value));
}

bool QuicDataWriter::WriteUInt48(uint64 value) {
  uint32 hi = value >> 32;
  uint32 lo = value & GG_UINT64_C(0x00000000FFFFFFFF);
  return WriteUInt32(lo) && WriteUInt16(hi);
}

bool QuicDataWriter::WriteUInt64(uint64 value) {
  return WriteBytes(&value, sizeof(value));
}

bool QuicDataWriter::WriteUFloat16(uint64 value) {
  uint16 result;
  if (value < (GG_UINT64_C(1) << kUFloat16MantissaEffectiveBits)) {
    // Fast path: either the value is denormalized, or has exponent zero.
    // Both cases are represented by the value itself.
    result = value;
  } else if (value >= kUFloat16MaxValue) {
    // Value is out of range; clamp it to the maximum representable.
    result = numeric_limits<uint16>::max();
  } else {
    // The highest bit is between position 13 and 42 (zero-based), which
    // corresponds to exponent 1-30. In the output, mantissa is from 0 to 10,
    // hidden bit is 11 and exponent is 11 to 15. Shift the highest bit to 11
    // and count the shifts.
    uint16 exponent = 0;
    for (uint16 offset = 16; offset > 0; offset /= 2) {
      // Right-shift the value until the highest bit is in position 11.
      // For offset of 16, 8, 4, 2 and 1 (binary search over 1-30),
      // shift if the bit is at or above 11 + offset.
      if (value >= (GG_UINT64_C(1) << (kUFloat16MantissaBits + offset))) {
        exponent += offset;
        value >>= offset;
      }
    }

    DCHECK_GE(exponent, 1);
    DCHECK_LE(exponent, kUFloat16MaxExponent);
    DCHECK_GE(value, GG_UINT64_C(1) << kUFloat16MantissaBits);
    DCHECK_LT(value, GG_UINT64_C(1) << kUFloat16MantissaEffectiveBits);

    // Hidden bit (position 11) is set. We should remove it and increment the
    // exponent. Equivalently, we just add it to the exponent.
    // This hides the bit.
    result = value + (exponent << kUFloat16MantissaBits);
  }

  return WriteBytes(&result, sizeof(result));
}

bool QuicDataWriter::WriteStringPiece16(StringPiece val) {
  if (val.length() > numeric_limits<uint16>::max()) {
    return false;
  }
  if (!WriteUInt16(val.size())) {
    return false;
  }
  return WriteBytes(val.data(), val.size());
}

bool QuicDataWriter::WriteIOVector(const IOVector& data) {
  char *dest = BeginWrite(data.TotalBufferSize());
  if (!dest) {
    return false;
  }
  for (size_t i = 0; i < data.Size(); ++i) {
    WriteBytes(data.iovec()[i].iov_base,  data.iovec()[i].iov_len);
  }

  return true;
}

char* QuicDataWriter::BeginWrite(size_t length) {
  if (length_ > capacity_) {
    return NULL;
  }

  if (capacity_ - length_ < length) {
    return NULL;
  }

#ifdef ARCH_CPU_64_BITS
  DCHECK_LE(length, numeric_limits<uint32>::max());
#endif

  return buffer_ + length_;
}

bool QuicDataWriter::WriteBytes(const void* data, size_t data_len) {
  char* dest = BeginWrite(data_len);
  if (!dest) {
    return false;
  }

  memcpy(dest, data, data_len);

  length_ += data_len;
  return true;
}

bool QuicDataWriter::WriteRepeatedByte(uint8 byte, size_t count) {
  char* dest = BeginWrite(count);
  if (!dest) {
    return false;
  }

  memset(dest, byte, count);

  length_ += count;
  return true;
}

void QuicDataWriter::WritePadding() {
  DCHECK_LE(length_, capacity_);
  if (length_ > capacity_) {
    return;
  }
  memset(buffer_ + length_, 0x00, capacity_ - length_);
  length_ = capacity_;
}

bool QuicDataWriter::WriteUInt8ToOffset(uint8 value, size_t offset) {
  if (offset >= capacity_) {
    LOG(DFATAL) << "offset: " << offset << " >= capacity: " << capacity_;
    return false;
  }
  size_t latched_length = length_;
  length_ = offset;
  bool success = WriteUInt8(value);
  DCHECK_LE(length_, latched_length);
  length_ = latched_length;
  return success;
}

bool QuicDataWriter::WriteUInt32ToOffset(uint32 value, size_t offset) {
  DCHECK_LT(offset, capacity_);
  size_t latched_length = length_;
  length_ = offset;
  bool success = WriteUInt32(value);
  DCHECK_LE(length_, latched_length);
  length_ = latched_length;
  return success;
}

bool QuicDataWriter::WriteUInt48ToOffset(uint64 value, size_t offset) {
  DCHECK_LT(offset, capacity_);
  size_t latched_length = length_;
  length_ = offset;
  bool success = WriteUInt48(value);
  DCHECK_LE(length_, latched_length);
  length_ = latched_length;
  return success;
}

}  // namespace net