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77 lines
2.8 KiB
77 lines
2.8 KiB
/*
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* Copyright 2021 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://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,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <cstdint>
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#include "bits_util.h"
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class Varint {
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public:
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// Maximum lengths of varint encoding of uint64
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static constexpr int kMax64 = 10;
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// REQUIRES "ptr" points to a buffer of length sufficient to hold "v".
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// EFFECTS Encodes "v" into "ptr" and returns a pointer to the
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// byte just past the last encoded byte.
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static char* Encode32(char* ptr, uint32_t v);
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static char* Encode64(char* ptr, uint64_t v);
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// EFFECTS Returns the encoding length of the specified value.
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static int Length64(uint64_t v);
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private:
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// A fully inlined version of Encode32: useful in the most time critical
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// routines, but its code size is large
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static char* Encode32Inline(char* ptr, uint32_t v);
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};
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inline int Varint::Length64(uint64_t v) {
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// This computes value == 0 ? 1 : floor(log2(v)) / 7 + 1 using an explicit
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// multiplication to implement the division of a number in the 1..63 range.
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// Explicit OR 0x1 to handle v == 0.
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uint32_t log2value = BitsUtil::Log2FloorNonZero64(v | 0x1);
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return static_cast<int>((log2value * 9 + 73) / 64);
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}
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inline char* Varint::Encode32Inline(char* sptr, uint32_t v) {
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// Operate on characters as unsigneds
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uint8_t* ptr = reinterpret_cast<uint8_t*>(sptr);
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static const uint32_t B = 128;
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if (v < (1 << 7)) {
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*(ptr++) = static_cast<uint8_t>(v);
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} else if (v < (1 << 14)) {
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*(ptr++) = static_cast<uint8_t>(v | B);
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*(ptr++) = static_cast<uint8_t>(v >> 7);
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} else if (v < (1 << 21)) {
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*(ptr++) = static_cast<uint8_t>(v | B);
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*(ptr++) = static_cast<uint8_t>((v >> 7) | B);
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*(ptr++) = static_cast<uint8_t>(v >> 14);
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} else if (v < (1 << 28)) {
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*(ptr++) = static_cast<uint8_t>(v | B);
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*(ptr++) = static_cast<uint8_t>((v >> 7) | B);
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*(ptr++) = static_cast<uint8_t>((v >> 14) | B);
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*(ptr++) = static_cast<uint8_t>(v >> 21);
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} else {
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*(ptr++) = static_cast<uint8_t>(v | B);
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*(ptr++) = static_cast<uint8_t>((v >> 7) | B);
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*(ptr++) = static_cast<uint8_t>((v >> 14) | B);
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*(ptr++) = static_cast<uint8_t>((v >> 21) | B);
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*(ptr++) = static_cast<uint8_t>(v >> 28);
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}
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return reinterpret_cast<char*>(ptr);
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}
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