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// StringCompression.cpp
// Implements the wrapping functions for compression and decompression
#include "Globals.h"
#include "ByteBuffer.h"
#include "StringCompression.h"
#include <libdeflate.h>
std::string_view Compression::Result::GetStringView() const
{
const auto View = GetView();
return { reinterpret_cast<const char *>(View.data()), View.size() };
}
ContiguousByteBufferView Compression::Result::GetView() const
{
// Get a generic std::byte * to what the variant is currently storing:
return
{
std::visit([](const auto & Buffer) -> const std::byte *
{
using Variant = std::decay_t<decltype(Buffer)>;
if constexpr (std::is_same_v<Variant, Compression::Result::Static>)
{
return Buffer.data();
}
else
{
return Buffer.get();
}
}, Storage), Size
};
}
Compression::Compressor::Compressor(int CompressionFactor)
{
m_Handle = libdeflate_alloc_compressor(CompressionFactor);
if (m_Handle == nullptr)
{
throw std::bad_alloc();
}
}
Compression::Compressor::~Compressor()
{
libdeflate_free_compressor(m_Handle);
}
template <auto Algorithm>
Compression::Result Compression::Compressor::Compress(const void * const Input, const size_t Size)
{
// First see if the stack buffer has enough space:
{
Result::Static Buffer = {static_cast<std::byte>(0)};
const auto BytesWrittenOut = Algorithm(m_Handle, Input, Size, Buffer.data(), Buffer.size());
if (BytesWrittenOut != 0)
{
return { Buffer, BytesWrittenOut };
}
}
// No it doesn't. Allocate space on the heap to write the compression result, increasing in powers of 2.
// This will either succeed, or except with bad_alloc.
auto DynamicCapacity = Result::StaticCapacity * 2;
while (true)
{
auto Dynamic = cpp20::make_unique_for_overwrite<Result::Dynamic::element_type[]>(DynamicCapacity);
const auto BytesWrittenOut = Algorithm(m_Handle, Input, Size, Dynamic.get(), DynamicCapacity);
if (BytesWrittenOut != 0)
{
return { std::move(Dynamic), BytesWrittenOut };
}
DynamicCapacity *= 2;
}
}
Compression::Result Compression::Compressor::CompressGZip(const ContiguousByteBufferView Input)
{
return Compress<&libdeflate_gzip_compress>(Input.data(), Input.size());
}
Compression::Result Compression::Compressor::CompressZLib(const ContiguousByteBufferView Input)
{
return Compress<&libdeflate_zlib_compress>(Input.data(), Input.size());
}
Compression::Result Compression::Compressor::CompressZLib(const void * const Input, const size_t Size)
{
return Compress<&libdeflate_zlib_compress>(Input, Size);
}
Compression::Extractor::Extractor()
{
m_Handle = libdeflate_alloc_decompressor();
if (m_Handle == nullptr)
{
throw std::bad_alloc();
}
}
Compression::Extractor::~Extractor()
{
libdeflate_free_decompressor(m_Handle);
}
Compression::Result Compression::Extractor::ExtractGZip(ContiguousByteBufferView Input)
{
return Extract<&libdeflate_gzip_decompress>(Input);
}
Compression::Result Compression::Extractor::ExtractZLib(ContiguousByteBufferView Input)
{
return Extract<&libdeflate_zlib_decompress>(Input);
}
Compression::Result Compression::Extractor::ExtractZLib(ContiguousByteBufferView Input, size_t UncompressedSize)
{
return Extract<&libdeflate_zlib_decompress>(Input, UncompressedSize);
}
template <auto Algorithm>
Compression::Result Compression::Extractor::Extract(const ContiguousByteBufferView Input)
{
// First see if the stack buffer has enough space:
{
Result::Static Buffer = {static_cast<std::byte>(0)};
size_t BytesWrittenOut;
switch (Algorithm(m_Handle, Input.data(), Input.size(), Buffer.data(), Buffer.size(), &BytesWrittenOut))
{
case LIBDEFLATE_SUCCESS: return { Buffer, BytesWrittenOut };
case LIBDEFLATE_INSUFFICIENT_SPACE: break;
default: throw std::runtime_error("Data extraction failed.");
}
}
// No it doesn't. Allocate space on the heap to write the compression result, increasing in powers of 2.
auto DynamicCapacity = Result::StaticCapacity * 2;
while (true)
{
size_t BytesWrittenOut;
auto Dynamic = cpp20::make_unique_for_overwrite<Result::Dynamic::element_type[]>(DynamicCapacity);
switch (Algorithm(m_Handle, Input.data(), Input.size(), Dynamic.get(), DynamicCapacity, &BytesWrittenOut))
{
case libdeflate_result::LIBDEFLATE_SUCCESS: return { std::move(Dynamic), BytesWrittenOut };
case libdeflate_result::LIBDEFLATE_INSUFFICIENT_SPACE:
{
DynamicCapacity *= 2;
continue;
}
default: throw std::runtime_error("Data extraction failed.");
}
}
}
template <auto Algorithm>
Compression::Result Compression::Extractor::Extract(const ContiguousByteBufferView Input, size_t UncompressedSize)
{
// Here we have the expected size after extraction, so directly use a suitable buffer size:
if (UncompressedSize <= Result::StaticCapacity)
{
if (
Result::Static Buffer;
Algorithm(m_Handle, Input.data(), Input.size(), Buffer.data(), UncompressedSize, nullptr) == libdeflate_result::LIBDEFLATE_SUCCESS
)
{
return { Buffer, UncompressedSize };
}
}
else if (
auto Dynamic = cpp20::make_unique_for_overwrite<Result::Dynamic::element_type[]>(UncompressedSize);
Algorithm(m_Handle, Input.data(), Input.size(), Dynamic.get(), UncompressedSize, nullptr) == libdeflate_result::LIBDEFLATE_SUCCESS
)
{
return { std::move(Dynamic), UncompressedSize };
}
throw std::runtime_error("Data extraction failed.");
}
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