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#pragma once
#include "byte_reader.h"
#include "byte_writer.h"
#include "traits.h"
#include "zigzag.h"
#include <util/system/types.h>
#include <cstddef>
#include <type_traits>
namespace NYsonPull {
namespace NDetail {
namespace NVarInt {
namespace NImpl {
template <typename T>
constexpr inline size_t max_size() {
return (8 * sizeof(T) - 1) / 7 + 1;
}
template <typename T>
inline size_t write(ui64 value, T&& consume) {
auto stop = false;
auto nwritten = size_t{0};
while (!stop) {
++nwritten;
auto byte = static_cast<ui8>(value | 0x80);
value >>= 7;
if (value == 0) {
stop = true;
byte &= 0x7F;
}
consume(byte);
}
return nwritten;
}
template <typename U>
inline bool read_fast(byte_reader<U>& reader, ui64* value) {
auto& buf = reader.stream().buffer();
auto* ptr = buf.pos();
ui32 b;
// Splitting into 32-bit pieces gives better performance on 32-bit
// processors.
ui32 part0 = 0, part1 = 0, part2 = 0;
b = *(ptr++);
part0 = (b & 0x7F);
if (!(b & 0x80))
goto done;
b = *(ptr++);
part0 |= (b & 0x7F) << 7;
if (!(b & 0x80))
goto done;
b = *(ptr++);
part0 |= (b & 0x7F) << 14;
if (!(b & 0x80))
goto done;
b = *(ptr++);
part0 |= (b & 0x7F) << 21;
if (!(b & 0x80))
goto done;
b = *(ptr++);
part1 = (b & 0x7F);
if (!(b & 0x80))
goto done;
b = *(ptr++);
part1 |= (b & 0x7F) << 7;
if (!(b & 0x80))
goto done;
b = *(ptr++);
part1 |= (b & 0x7F) << 14;
if (!(b & 0x80))
goto done;
b = *(ptr++);
part1 |= (b & 0x7F) << 21;
if (!(b & 0x80))
goto done;
b = *(ptr++);
part2 = (b & 0x7F);
if (!(b & 0x80))
goto done;
b = *(ptr++);
part2 |= (b & 0x7F) << 7;
if (!(b & 0x80))
goto done;
// We have overrun the maximum size of a Varint (10 bytes). The data
// must be corrupt.
return false;
done:
reader.advance(ptr - buf.pos());
*value = (static_cast<ui64>(part0)) | (static_cast<ui64>(part1) << 28) | (static_cast<ui64>(part2) << 56);
return true;
}
template <typename U>
inline bool read_fast(byte_reader<U>& reader, ui32* value) {
// Fast path: We have enough bytes left in the buffer to guarantee that
// this read won't cross the end, so we can skip the checks.
auto& buf = reader.stream().buffer();
auto* ptr = buf.pos();
ui32 b;
ui32 result;
b = *(ptr++);
result = (b & 0x7F);
if (!(b & 0x80))
goto done;
b = *(ptr++);
result |= (b & 0x7F) << 7;
if (!(b & 0x80))
goto done;
b = *(ptr++);
result |= (b & 0x7F) << 14;
if (!(b & 0x80))
goto done;
b = *(ptr++);
result |= (b & 0x7F) << 21;
if (!(b & 0x80))
goto done;
b = *(ptr++);
result |= b << 28;
if (!(b & 0x80))
goto done;
// FIXME
// If the input is larger than 32 bits, we still need to read it all
// and discard the high-order bits.
for (size_t i = 0; i < max_size<ui64>() - max_size<ui32>(); i++) {
b = *(ptr++);
if (!(b & 0x80))
goto done;
}
// We have overrun the maximum size of a Varint (10 bytes). Assume
// the data is corrupt.
return false;
done:
reader.advance(ptr - buf.pos());
*value = result;
return true;
}
template <typename U>
inline bool read_slow(byte_reader<U>& reader, ui64* value) {
// Slow path: This read might cross the end of the buffer, so we
// need to check and refresh the buffer if and when it does.
auto& buf = reader.stream().buffer();
ui64 result = 0;
int count = 0;
ui32 b;
do {
if (count == max_size<ui64>()) {
return false;
}
reader.fill_buffer();
if (reader.stream().at_end()) {
return false;
}
b = *buf.pos();
result |= static_cast<ui64>(b & 0x7F) << (7 * count);
reader.advance(1);
++count;
} while (b & 0x80);
*value = result;
return true;
}
template <typename U>
inline bool read_slow(byte_reader<U>& reader, ui32* value) {
ui64 result;
// fallback to 64-bit reading
if (read_slow(reader, &result) && result <= std::numeric_limits<ui32>::max()) {
*value = static_cast<ui32>(result);
return true;
}
return false;
}
// Following functions is an adaptation
// of Protobuf code from coded_stream.cc
template <typename T, typename U>
inline bool read_dispatch(byte_reader<U>& reader, T* value) {
auto& buf = reader.stream().buffer();
// NOTE: checking for 64-bit max_size(), since 32-bit
// read_fast() might fallback to 64-bit reading
if (buf.available() >= max_size<ui64>() ||
// Optimization: If the Varint ends at exactly the end of the buffer,
// we can detect that and still use the fast path.
(!buf.is_empty() && !(buf.end()[-1] & 0x80)))
{
return read_fast(reader, value);
} else {
// Really slow case: we will incur the cost of an extra function call here,
// but moving this out of line reduces the size of this function, which
// improves the common case. In micro benchmarks, this is worth about 10-15%
return read_slow(reader, value);
}
}
}
// Various functions to read/write varints.
// Returns the number of bytes written.
template <typename T>
inline NTraits::if_unsigned<T, size_t> write(ui8* data, T value) {
return NImpl::write(
static_cast<ui64>(value),
[&](ui8 byte) { *data++ = byte; });
}
template <typename T>
inline NTraits::if_signed<T, size_t> write(ui8* data, T value) {
return NImpl::write(
static_cast<ui64>(NZigZag::encode(value)),
[&](ui8 byte) { *data++ = byte; });
}
template <typename T, typename U>
inline void write(byte_writer<U>& stream, T value) {
ui8 data[NImpl::max_size<T>()];
auto size = write(data, value);
stream.write(data, size);
}
template <typename T, typename U>
inline NTraits::if_unsigned<T, T> read(byte_reader<U>& reader) {
auto value = T{};
auto& buf = reader.stream().buffer();
if (!buf.is_empty() && *buf.pos() < 0x80) {
value = *buf.pos();
reader.advance(1);
return value;
}
if (Y_UNLIKELY(!NImpl::read_dispatch(reader, &value))) {
reader.fail("Error parsing varint value");
}
return value;
}
template <typename T, typename U>
inline NTraits::if_signed<T, T> read(byte_reader<U>& reader) {
return NZigZag::decode(
read<NTraits::to_unsigned<T>>(reader));
}
}
} // namespace NDetail
}
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