net/quic/quic_data_writer.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/quic/quic_data_writer.h"
   6
   7 #include <algorithm>
   8 #include <limits>
   9 #include <string>
  10
  11 #include "base/basictypes.h"
  12 #include "base/logging.h"
  13
  14 using base::StringPiece;
  15 using std::numeric_limits;
  16
  17 namespace net {
  18
  19 QuicDataWriter::QuicDataWriter(size_t size)
  20     : buffer_(new char[size]),
  21       capacity_(size),
  22       length_(0) {
  23 }
  24
  25 QuicDataWriter::~QuicDataWriter() {
  26   delete[] buffer_;
  27 }
  28
  29 char* QuicDataWriter::take() {
  30   char* rv = buffer_;
  31   buffer_ = NULL;
  32   capacity_ = 0;
  33   length_ = 0;
  34   return rv;
  35 }
  36
  37 bool QuicDataWriter::WriteUInt8(uint8 value) {
  38   return WriteBytes(&value, sizeof(value));
  39 }
  40
  41 bool QuicDataWriter::WriteUInt16(uint16 value) {
  42   return WriteBytes(&value, sizeof(value));
  43 }
  44
  45 bool QuicDataWriter::WriteUInt32(uint32 value) {
  46   return WriteBytes(&value, sizeof(value));
  47 }
  48
  49 bool QuicDataWriter::WriteUInt48(uint64 value) {
  50   uint32 hi = value >> 32;
  51   uint32 lo = value & GG_UINT64_C(0x00000000FFFFFFFF);
  52   return WriteUInt32(lo) && WriteUInt16(hi);
  53 }
  54
  55 bool QuicDataWriter::WriteUInt64(uint64 value) {
  56   return WriteBytes(&value, sizeof(value));
  57 }
  58
  59 bool QuicDataWriter::WriteUFloat16(uint64 value) {
  60   uint16 result;
  61   if (value < (GG_UINT64_C(1) << kUFloat16MantissaEffectiveBits)) {
  62     // Fast path: either the value is denormalized, or has exponent zero.
  63     // Both cases are represented by the value itself.
  64     result = value;
  65   } else if (value >= kUFloat16MaxValue) {
  66     // Value is out of range; clamp it to the maximum representable.
  67     result = numeric_limits<uint16>::max();
  68   } else {
  69     // The highest bit is between position 13 and 42 (zero-based), which
  70     // corresponds to exponent 1-30. In the output, mantissa is from 0 to 10,
  71     // hidden bit is 11 and exponent is 11 to 15. Shift the highest bit to 11
  72     // and count the shifts.
  73     uint16 exponent = 0;
  74     for (uint16 offset = 16; offset > 0; offset /= 2) {
  75       // Right-shift the value until the highest bit is in position 11.
  76       // For offset of 16, 8, 4, 2 and 1 (binary search over 1-30),
  77       // shift if the bit is at or above 11 + offset.
  78       if (value >= (GG_UINT64_C(1) << (kUFloat16MantissaBits + offset))) {
  79         exponent += offset;
  80         value >>= offset;
  81       }
  82     }
  83
  84     DCHECK_GE(exponent, 1);
  85     DCHECK_LE(exponent, kUFloat16MaxExponent);
  86     DCHECK_GE(value, GG_UINT64_C(1) << kUFloat16MantissaBits);
  87     DCHECK_LT(value, GG_UINT64_C(1) << kUFloat16MantissaEffectiveBits);
  88
  89     // Hidden bit (position 11) is set. We should remove it and increment the
  90     // exponent. Equivalently, we just add it to the exponent.
  91     // This hides the bit.
  92     result = value + (exponent << kUFloat16MantissaBits);
  93   }
  94
  95   return WriteBytes(&result, sizeof(result));
  96 }
  97
  98 bool QuicDataWriter::WriteStringPiece16(StringPiece val) {
  99   if (val.length() > numeric_limits<uint16>::max()) {
 100     return false;
 101   }
 102   if (!WriteUInt16(val.size())) {
 103     return false;
 104   }
 105   return WriteBytes(val.data(), val.size());
 106 }
 107
 108 bool QuicDataWriter::WriteIOVector(const IOVector& data) {
 109   char *dest = BeginWrite(data.TotalBufferSize());
 110   if (!dest) {
 111     return false;
 112   }
 113   for (size_t i = 0; i < data.Size(); ++i) {
 114     WriteBytes(data.iovec()[i].iov_base,  data.iovec()[i].iov_len);
 115   }
 116
 117   return true;
 118 }
 119
 120 char* QuicDataWriter::BeginWrite(size_t length) {
 121   if (length_ > capacity_) {
 122     return NULL;
 123   }
 124
 125   if (capacity_ - length_ < length) {
 126     return NULL;
 127   }
 128
 129 #ifdef ARCH_CPU_64_BITS
 130   DCHECK_LE(length, numeric_limits<uint32>::max());
 131 #endif
 132
 133   return buffer_ + length_;
 134 }
 135
 136 bool QuicDataWriter::WriteBytes(const void* data, size_t data_len) {
 137   char* dest = BeginWrite(data_len);
 138   if (!dest) {
 139     return false;
 140   }
 141
 142   memcpy(dest, data, data_len);
 143
 144   length_ += data_len;
 145   return true;
 146 }
 147
 148 bool QuicDataWriter::WriteRepeatedByte(uint8 byte, size_t count) {
 149   char* dest = BeginWrite(count);
 150   if (!dest) {
 151     return false;
 152   }
 153
 154   memset(dest, byte, count);
 155
 156   length_ += count;
 157   return true;
 158 }
 159
 160 void QuicDataWriter::WritePadding() {
 161   DCHECK_LE(length_, capacity_);
 162   if (length_ > capacity_) {
 163     return;
 164   }
 165   memset(buffer_ + length_, 0x00, capacity_ - length_);
 166   length_ = capacity_;
 167 }
 168
 169 bool QuicDataWriter::WriteUInt8ToOffset(uint8 value, size_t offset) {
 170   DCHECK_LT(offset, capacity_);
 171   size_t latched_length = length_;
 172   length_ = offset;
 173   bool success = WriteUInt8(value);
 174   DCHECK_LE(length_, latched_length);
 175   length_ = latched_length;
 176   return success;
 177 }
 178
 179 bool QuicDataWriter::WriteUInt32ToOffset(uint32 value, size_t offset) {
 180   DCHECK_LT(offset, capacity_);
 181   size_t latched_length = length_;
 182   length_ = offset;
 183   bool success = WriteUInt32(value);
 184   DCHECK_LE(length_, latched_length);
 185   length_ = latched_length;
 186   return success;
 187 }
 188
 189 bool QuicDataWriter::WriteUInt48ToOffset(uint64 value, size_t offset) {
 190   DCHECK_LT(offset, capacity_);
 191   size_t latched_length = length_;
 192   length_ = offset;
 193   bool success = WriteUInt48(value);
 194   DCHECK_LE(length_, latched_length);
 195   length_ = latched_length;
 196   return success;
 197 }
 198
 199 }  // namespace net