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#pragma once
#include "codecs.h"
#include <util/generic/array_ref.h>
#include <util/generic/typetraits.h>
#include <util/generic/bitops.h>
#include <util/string/cast.h>
namespace NCodecs {
template <typename T = ui64, bool UnsignedDelta = true>
class TDeltaCodec: public ICodec {
static_assert(std::is_integral<T>::value, "expect std::is_integral<T>::value");
public:
using TUnsigned = std::make_unsigned_t<T>;
using TSigned = std::make_signed_t<T>;
using TDelta = std::conditional_t<UnsignedDelta, TUnsigned, TSigned>;
private:
const TDelta MinDelta{Min<TDelta>()};
const TDelta MaxDelta{Max<TDelta>() - 1};
const TDelta InvalidDelta{MaxDelta + 1};
Y_FORCE_INLINE static TDelta AddSafe(TUnsigned a, TUnsigned b) {
return a + b;
}
Y_FORCE_INLINE static TDelta SubSafe(TUnsigned a, TUnsigned b) {
return a - b;
}
public:
struct TDecoder {
const TDelta InvalidDelta{Max<TDelta>()};
T Last = 0;
T Result = 0;
bool First = true;
bool Invalid = false;
Y_FORCE_INLINE bool Decode(TDelta t) {
if (Y_UNLIKELY(First)) {
First = false;
Result = Last = t;
return true;
}
if (Y_UNLIKELY(Invalid)) {
Invalid = false;
Last = 0;
Result = t;
return true;
}
Result = (Last += t);
Invalid = t == InvalidDelta;
return !Invalid;
}
};
public:
static TStringBuf MyName();
TDeltaCodec() {
MyTraits.SizeOfInputElement = sizeof(T);
MyTraits.AssumesStructuredInput = true;
}
TString GetName() const override {
return ToString(MyName());
}
template <class TItem>
static void AppendTo(TBuffer& b, TItem t) {
b.Append((char*)&t, sizeof(t));
}
ui8 Encode(TStringBuf s, TBuffer& b) const override {
b.Clear();
if (s.empty()) {
return 0;
}
b.Reserve(s.size());
TArrayRef<const T> tin{(const T*)s.data(), s.size() / sizeof(T)};
const T* it = tin.begin();
TDelta last = *(it++);
AppendTo(b, last);
TDelta maxt = SubSafe(MaxDelta, last);
TDelta mint = AddSafe(MinDelta, last);
for (; it != tin.end(); ++it) {
TDelta t = *it;
if (Y_LIKELY((t >= mint) & (t <= maxt))) {
AppendTo(b, t - last);
last = t;
maxt = SubSafe(MaxDelta, last);
mint = AddSafe(MinDelta, last);
} else {
// delta overflow
AppendTo(b, InvalidDelta);
AppendTo(b, t);
last = 0;
maxt = MaxDelta;
mint = MinDelta;
}
}
return 0;
}
void Decode(TStringBuf s, TBuffer& b) const override {
b.Clear();
if (s.empty()) {
return;
}
b.Reserve(s.size());
TArrayRef<const T> tin{(const T*)s.data(), s.size() / sizeof(T)};
TDecoder dec;
for (const T* it = tin.begin(); it != tin.end(); ++it) {
T tmp;
memcpy(&tmp, it, sizeof(tmp));
if (dec.Decode(tmp)) {
AppendTo(b, dec.Result);
}
}
}
protected:
void DoLearn(ISequenceReader&) override {
}
};
}
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