ff43541927
Before this CL, when we encoded a sequence with a non-existent base, we pretended that the delta was 0, and the first delta was based on that. However, in a sequence where the deltas are small, but where the first element is big, that would produce unnecessarily wide deltas. Therefore, we change the behavior in cases where the base is non-existent, to encode the first existent value (if any) as a varint; the delta width may then be smaller. This CL include two piggy-backed changes: 1. Varint encoding/decoding moved to its own file (and an additional flavor added). 2. The unit tests for delta encoding are further parameterized with a random seed. Bug: webrtc:8111 Change-Id: I76fff577c86d019c8334bf74b76bd35db06ff68d Reviewed-on: https://webrtc-review.googlesource.com/c/107860 Reviewed-by: Björn Terelius <terelius@webrtc.org> Commit-Queue: Elad Alon <eladalon@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25395}
81 lines
2.1 KiB
C++
81 lines
2.1 KiB
C++
/*
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* Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "logging/rtc_event_log/encoder/varint.h"
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#include "rtc_base/checks.h"
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// TODO(eladalon): Add unit tests.
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namespace webrtc {
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const size_t kMaxVarIntLengthBytes = 10; // ceil(64 / 7.0) is 10.
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std::string EncodeVarInt(uint64_t input) {
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std::string output;
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output.reserve(kMaxVarIntLengthBytes);
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do {
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uint8_t byte = static_cast<uint8_t>(input & 0x7f);
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input >>= 7;
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if (input > 0) {
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byte |= 0x80;
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}
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output += byte;
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} while (input > 0);
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RTC_DCHECK_GE(output.size(), 1u);
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RTC_DCHECK_LE(output.size(), kMaxVarIntLengthBytes);
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return output;
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}
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// There is some code duplication between the flavors of this function.
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// For performance's sake, it's best to just keep it.
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size_t DecodeVarInt(absl::string_view input, uint64_t* output) {
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RTC_DCHECK(output);
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uint64_t decoded = 0;
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for (size_t i = 0; i < input.length() && i < kMaxVarIntLengthBytes; ++i) {
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decoded += (static_cast<uint64_t>(input[i] & 0x7f)
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<< static_cast<uint64_t>(7 * i));
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if (!(input[i] & 0x80)) {
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*output = decoded;
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return i + 1;
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}
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}
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return 0;
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}
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// There is some code duplication between the flavors of this function.
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// For performance's sake, it's best to just keep it.
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size_t DecodeVarInt(rtc::BitBuffer* input, uint64_t* output) {
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RTC_DCHECK(output);
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uint64_t decoded = 0;
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for (size_t i = 0; i < kMaxVarIntLengthBytes; ++i) {
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uint8_t byte;
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if (!input->ReadUInt8(&byte)) {
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return 0;
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}
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decoded +=
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(static_cast<uint64_t>(byte & 0x7f) << static_cast<uint64_t>(7 * i));
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if (!(byte & 0x80)) {
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*output = decoded;
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return i + 1;
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}
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}
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return 0;
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}
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} // namespace webrtc
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