blob: 87f4981bdf1e8765dbed5869301f20a774a3f138 [file] [log] [blame]
// Copyright 2016 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 "http2/hpack/varint/hpack_varint_encoder.h"
#include <limits>
#include "http2/platform/api/http2_logging.h"
namespace http2 {
// static
void HpackVarintEncoder::Encode(uint8_t high_bits,
uint8_t prefix_length,
uint64_t varint,
std::string* output) {
QUICHE_DCHECK_LE(1u, prefix_length);
QUICHE_DCHECK_LE(prefix_length, 8u);
// prefix_mask defines the sequence of low-order bits of the first byte
// that encode the prefix of the value. It is also the marker in those bits
// of the first byte indicating that at least one extension byte is needed.
const uint8_t prefix_mask = (1 << prefix_length) - 1;
QUICHE_DCHECK_EQ(0, high_bits & prefix_mask);
if (varint < prefix_mask) {
// The integer fits into the prefix in its entirety.
unsigned char first_byte = high_bits | static_cast<unsigned char>(varint);
// Extension bytes are needed.
unsigned char first_byte = high_bits | prefix_mask;
varint -= prefix_mask;
while (varint >= 128) {
// Encode the next seven bits, with continuation bit set to one.
output->push_back(0b10000000 | (varint % 128));
varint >>= 7;
// Encode final seven bits, with continuation bit set to zero.
} // namespace http2