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// Author: Artyom Polkovnikov.
// Different variants of Varint encoding/decoding.
#pragma once
#include "coding/reader.hpp"
#include "coding/writer.hpp"
#include "base/assert.hpp"
#include "std/cstdint.hpp"
#include "std/vector.hpp"
// Encode Varint by appending to vector of bytes.
inline void VarintEncode(vector<uint8_t> & dst, uint64_t n)
{
if (n == 0)
{
dst.push_back(0);
}
else
{
while (n != 0)
{
uint8_t b = n & 0x7F;
n >>= 7;
b |= n == 0 ? 0 : 0x80;
dst.push_back(b);
}
}
}
// Encode varint using bytes Writer.
inline void VarintEncode(Writer & writer, uint64_t n)
{
if (n == 0)
{
writer.Write(&n, 1);
}
else
{
while (n != 0)
{
uint8_t b = n & 0x7F;
n >>= 7;
b |= n == 0 ? 0 : 0x80;
writer.Write(&b, 1);
}
}
}
// Deocde varint at given pointer and offset, offset is incremented after encoding.
inline uint64_t VarintDecode(void * src, uint64_t & offset)
{
uint64_t n = 0;
int shift = 0;
while (1)
{
uint8_t b = *(((uint8_t*)src) + offset);
CHECK_LESS_OR_EQUAL(shift, 56, ());
n |= uint64_t(b & 0x7F) << shift;
++offset;
if ((b & 0x80) == 0) break;
shift += 7;
}
return n;
}
// Decode varint using bytes Reader, offset is incremented after decoding.
inline uint64_t VarintDecode(Reader & reader, uint64_t & offset)
{
uint64_t n = 0;
int shift = 0;
while (1)
{
uint8_t b = 0;
reader.Read(offset, &b, 1);
CHECK_LESS_OR_EQUAL(shift, 56, ());
n |= uint64_t(b & 0x7F) << shift;
++offset;
if ((b & 0x80) == 0) break;
shift += 7;
}
return n;
}
// Reverse decode varint. Offset should point to last byte of decoded varint.
// It is compulsory that there is at least one encoded varint before this varint.
// After decoding offset points to the last byte of previous varint.
inline uint64_t VarintDecodeReverse(Reader & reader, uint64_t & offset)
{
uint8_t b = 0;
do
{
--offset;
reader.Read(offset, &b, 1);
}
while ((b & 0x80) != 0);
uint64_t prevLastEncodedByteOffset = offset;
++offset;
uint64_t num = VarintDecode(reader, offset);
offset = prevLastEncodedByteOffset;
return num;
}
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