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https://fuchsia.googlesource.com/third_party/pigweed.googlesource.com/pigweed/pigweed
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8c493bbf76
Change-Id: Ieff83592399946000fc806a037b0f5ffcaa3bd10
78 lines
2.1 KiB
C++
78 lines
2.1 KiB
C++
// Copyright 2019 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#include "pw_varint/varint.h"
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#include <algorithm>
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namespace pw::varint {
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namespace {
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constexpr int64_t ZigZagDecode64(uint64_t n) {
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return static_cast<int64_t>((n >> 1) ^ (~(n & 1) + 1));
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}
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} // namespace
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size_t EncodeLittleEndianBase128(uint64_t integer,
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const span<uint8_t>& output) {
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size_t written = 0;
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do {
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if (written >= output.size()) {
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return 0;
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}
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// Grab 7 bits; the eighth bit is set to 1 to indicate more data coming.
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output[written++] = static_cast<uint8_t>(integer) | '\x80';
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integer >>= 7;
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} while (integer != 0u);
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output[written - 1] &= '\x7f'; // clear the top bit of the last byte
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return written;
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}
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size_t DecodeVarint(const span<const uint8_t>& input, int64_t* value) {
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const size_t bytes = DecodeVarint(input, reinterpret_cast<uint64_t*>(value));
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*value = ZigZagDecode64(*value);
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return bytes;
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}
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size_t DecodeVarint(const span<const uint8_t>& input, uint64_t* value) {
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uint64_t decoded_value = 0;
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uint_fast8_t count = 0;
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// The largest 64-bit ints require 10 B.
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const size_t max_count = std::min(kMaxVarintSizeBytes, input.size());
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while (true) {
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if (count >= max_count) {
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return 0;
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}
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// Add the bottom seven bits of the next byte to the result.
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decoded_value |= static_cast<uint64_t>(input[count] & '\x7f')
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<< (7 * count);
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// Stop decoding if the top bit is not set.
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if ((input[count++] & '\x80') == 0) {
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break;
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}
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}
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*value = decoded_value;
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return count;
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}
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} // namespace pw::varint
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