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// 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 "quiche/quic/core/quic_data_reader.h"
#include "absl/strings/string_view.h"
#include "quiche/quic/core/quic_packets.h"
#include "quiche/quic/core/quic_utils.h"
#include "quiche/quic/platform/api/quic_bug_tracker.h"
#include "quiche/quic/platform/api/quic_flags.h"
#include "quiche/common/quiche_endian.h"
namespace quic {
QuicDataReader::QuicDataReader(absl::string_view data)
: quiche::QuicheDataReader(data) {}
QuicDataReader::QuicDataReader(const char* data, const size_t len)
: QuicDataReader(data, len, quiche::NETWORK_BYTE_ORDER) {}
QuicDataReader::QuicDataReader(const char* data, const size_t len,
quiche::Endianness endianness)
: quiche::QuicheDataReader(data, len, endianness) {}
bool QuicDataReader::ReadUFloat16(uint64_t* result) {
uint16_t value;
if (!ReadUInt16(&value)) {
return false;
}
*result = value;
if (*result < (1 << kUFloat16MantissaEffectiveBits)) {
// Fast path: either the value is denormalized (no hidden bit), or
// normalized (hidden bit set, exponent offset by one) with exponent zero.
// Zero exponent offset by one sets the bit exactly where the hidden bit is.
// So in both cases the value encodes itself.
return true;
}
uint16_t exponent =
value >> kUFloat16MantissaBits; // No sign extend on uint!
// After the fast pass, the exponent is at least one (offset by one).
// Un-offset the exponent.
--exponent;
QUICHE_DCHECK_GE(exponent, 1);
QUICHE_DCHECK_LE(exponent, kUFloat16MaxExponent);
// Here we need to clear the exponent and set the hidden bit. We have already
// decremented the exponent, so when we subtract it, it leaves behind the
// hidden bit.
*result -= exponent << kUFloat16MantissaBits;
*result <<= exponent;
QUICHE_DCHECK_GE(*result,
static_cast<uint64_t>(1 << kUFloat16MantissaEffectiveBits));
QUICHE_DCHECK_LE(*result, kUFloat16MaxValue);
return true;
}
bool QuicDataReader::ReadConnectionId(QuicConnectionId* connection_id,
uint8_t length) {
if (length == 0) {
connection_id->set_length(0);
return true;
}
if (BytesRemaining() < length) {
return false;
}
connection_id->set_length(length);
const bool ok =
ReadBytes(connection_id->mutable_data(), connection_id->length());
QUICHE_DCHECK(ok);
return ok;
}
bool QuicDataReader::ReadLengthPrefixedConnectionId(
QuicConnectionId* connection_id) {
uint8_t connection_id_length;
if (!ReadUInt8(&connection_id_length)) {
return false;
}
return ReadConnectionId(connection_id, connection_id_length);
}
QuicVariableLengthIntegerLength QuicDataReader::PeekVarInt62Length() {
QUICHE_DCHECK_EQ(endianness(), quiche::NETWORK_BYTE_ORDER);
const unsigned char* next =
reinterpret_cast<const unsigned char*>(data() + pos());
if (BytesRemaining() == 0) {
return VARIABLE_LENGTH_INTEGER_LENGTH_0;
}
return static_cast<QuicVariableLengthIntegerLength>(
1 << ((*next & 0b11000000) >> 6));
}
// Read an IETF/QUIC formatted 62-bit Variable Length Integer.
//
// Performance notes
//
// Measurements and experiments showed that unrolling the four cases
// like this and dereferencing next_ as we do (*(next_+n) --- and then
// doing a single pos_+=x at the end) gains about 10% over making a
// loop and dereferencing next_ such as *(next_++)
//
// Using a register for pos_ was not helpful.
//
// Branches are ordered to increase the likelihood of the first being
// taken.
//
// Low-level optimization is useful here because this function will be
// called frequently, leading to outsize benefits.
bool QuicDataReader::ReadVarInt62(uint64_t* result) {
QUICHE_DCHECK_EQ(endianness(), quiche::NETWORK_BYTE_ORDER);
size_t remaining = BytesRemaining();
const unsigned char* next =
reinterpret_cast<const unsigned char*>(data() + pos());
if (remaining != 0) {
switch (*next & 0xc0) {
case 0xc0:
// Leading 0b11...... is 8 byte encoding
if (remaining >= 8) {
*result = (static_cast<uint64_t>((*(next)) & 0x3f) << 56) +
(static_cast<uint64_t>(*(next + 1)) << 48) +
(static_cast<uint64_t>(*(next + 2)) << 40) +
(static_cast<uint64_t>(*(next + 3)) << 32) +
(static_cast<uint64_t>(*(next + 4)) << 24) +
(static_cast<uint64_t>(*(next + 5)) << 16) +
(static_cast<uint64_t>(*(next + 6)) << 8) +
(static_cast<uint64_t>(*(next + 7)) << 0);
AdvancePos(8);
return true;
}
return false;
case 0x80:
// Leading 0b10...... is 4 byte encoding
if (remaining >= 4) {
*result = (((*(next)) & 0x3f) << 24) + (((*(next + 1)) << 16)) +
(((*(next + 2)) << 8)) + (((*(next + 3)) << 0));
AdvancePos(4);
return true;
}
return false;
case 0x40:
// Leading 0b01...... is 2 byte encoding
if (remaining >= 2) {
*result = (((*(next)) & 0x3f) << 8) + (*(next + 1));
AdvancePos(2);
return true;
}
return false;
case 0x00:
// Leading 0b00...... is 1 byte encoding
*result = (*next) & 0x3f;
AdvancePos(1);
return true;
}
}
return false;
}
bool QuicDataReader::ReadStringPieceVarInt62(absl::string_view* result) {
uint64_t result_length;
if (!ReadVarInt62(&result_length)) {
return false;
}
return ReadStringPiece(result, result_length);
}
#undef ENDPOINT // undef for jumbo builds
} // namespace quic
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