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 <stdint.h>
   8 #include <algorithm>
   9 #include <limits>
  10
  11 using base::StringPiece;
  12 using std::numeric_limits;
  13
  14 namespace net {
  15
  16 QuicDataWriter::QuicDataWriter(size_t size, char* buffer)
  17     : buffer_(buffer), capacity_(size), length_(0) {
  18 }
  19
  20 QuicDataWriter::~QuicDataWriter() {
  21 }
  22
  23 char* QuicDataWriter::data() {
  24   return buffer_;
  25 }
  26
  27 bool QuicDataWriter::WriteUInt8(uint8 value) {
  28   return WriteBytes(&value, sizeof(value));
  29 }
  30
  31 bool QuicDataWriter::WriteUInt16(uint16 value) {
  32   return WriteBytes(&value, sizeof(value));
  33 }
  34
  35 bool QuicDataWriter::WriteUInt32(uint32 value) {
  36   return WriteBytes(&value, sizeof(value));
  37 }
  38
  39 bool QuicDataWriter::WriteUInt48(uint64 value) {
  40   uint16 hi = static_cast<uint16>(value >> 32);
  41   uint32 lo = static_cast<uint32>(value);
  42   return WriteUInt32(lo) && WriteUInt16(hi);
  43 }
  44
  45 bool QuicDataWriter::WriteUInt64(uint64 value) {
  46   return WriteBytes(&value, sizeof(value));
  47 }
  48
  49 bool QuicDataWriter::WriteUFloat16(uint64 value) {
  50   uint16 result;
  51   if (value < (UINT64_C(1) << kUFloat16MantissaEffectiveBits)) {
  52     // Fast path: either the value is denormalized, or has exponent zero.
  53     // Both cases are represented by the value itself.
  54     result = static_cast<uint16>(value);
  55   } else if (value >= kUFloat16MaxValue) {
  56     // Value is out of range; clamp it to the maximum representable.
  57     result = numeric_limits<uint16>::max();
  58   } else {
  59     // The highest bit is between position 13 and 42 (zero-based), which
  60     // corresponds to exponent 1-30. In the output, mantissa is from 0 to 10,
  61     // hidden bit is 11 and exponent is 11 to 15. Shift the highest bit to 11
  62     // and count the shifts.
  63     uint16 exponent = 0;
  64     for (uint16 offset = 16; offset > 0; offset /= 2) {
  65       // Right-shift the value until the highest bit is in position 11.
  66       // For offset of 16, 8, 4, 2 and 1 (binary search over 1-30),
  67       // shift if the bit is at or above 11 + offset.
  68       if (value >= (UINT64_C(1) << (kUFloat16MantissaBits + offset))) {
  69         exponent += offset;
  70         value >>= offset;
  71       }
  72     }
  73
  74     DCHECK_GE(exponent, 1);
  75     DCHECK_LE(exponent, kUFloat16MaxExponent);
  76     DCHECK_GE(value, UINT64_C(1) << kUFloat16MantissaBits);
  77     DCHECK_LT(value, UINT64_C(1) << kUFloat16MantissaEffectiveBits);
  78
  79     // Hidden bit (position 11) is set. We should remove it and increment the
  80     // exponent. Equivalently, we just add it to the exponent.
  81     // This hides the bit.
  82     result = static_cast<uint16>(value + (exponent << kUFloat16MantissaBits));
  83   }
  84
  85   return WriteBytes(&result, sizeof(result));
  86 }
  87
  88 bool QuicDataWriter::WriteStringPiece16(StringPiece val) {
  89   if (val.size() > numeric_limits<uint16>::max()) {
  90     return false;
  91   }
  92   if (!WriteUInt16(static_cast<uint16>(val.size()))) {
  93     return false;
  94   }
  95   return WriteBytes(val.data(), val.size());
  96 }
  97
  98 char* QuicDataWriter::BeginWrite(size_t length) {
  99   if (length_ > capacity_) {
 100     return nullptr;
 101   }
 102
 103   if (capacity_ - length_ < length) {
 104     return nullptr;
 105   }
 106
 107 #ifdef ARCH_CPU_64_BITS
 108   DCHECK_LE(length, std::numeric_limits<uint32>::max());
 109 #endif
 110
 111   return buffer_ + length_;
 112 }
 113
 114 bool QuicDataWriter::WriteBytes(const void* data, size_t data_len) {
 115   char* dest = BeginWrite(data_len);
 116   if (!dest) {
 117     return false;
 118   }
 119
 120   memcpy(dest, data, data_len);
 121
 122   length_ += data_len;
 123   return true;
 124 }
 125
 126 bool QuicDataWriter::WriteRepeatedByte(uint8 byte, size_t count) {
 127   char* dest = BeginWrite(count);
 128   if (!dest) {
 129     return false;
 130   }
 131
 132   memset(dest, byte, count);
 133
 134   length_ += count;
 135   return true;
 136 }
 137
 138 void QuicDataWriter::WritePadding() {
 139   DCHECK_LE(length_, capacity_);
 140   if (length_ > capacity_) {
 141     return;
 142   }
 143   memset(buffer_ + length_, 0x00, capacity_ - length_);
 144   length_ = capacity_;
 145 }
 146
 147
 148 }  // namespace net