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54 lines
1.9 KiB
C++
54 lines
1.9 KiB
C++
#pragma once
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#include <common/types.h>
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#include <Compression/ICompressionCodec.h>
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namespace DB
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{
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/// Get 64 integer valuses, makes 64x64 bit matrix, transpose it and crop unused bits (most significant zeroes).
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/// In example, if we have UInt8 with only 0 and 1 inside 64xUInt8 would be compressed into 1xUInt64.
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/// It detects unused bits by calculating min and max values of data part, saving them in header in compression phase.
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/// There's a special case with signed integers parts with crossing zero data. Here it stores one more bit to detect sign of value.
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class CompressionCodecT64 : public ICompressionCodec
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{
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public:
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static constexpr UInt32 HEADER_SIZE = 1 + 2 * sizeof(UInt64);
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static constexpr UInt32 MAX_COMPRESSED_BLOCK_SIZE = sizeof(UInt64) * 64;
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/// There're 2 compression variants:
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/// Byte - transpose bit matrix by bytes (only the last not full byte is transposed by bits). It's default.
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/// Bits - full bit-transpose of the bit matrix. It uses more resources and leads to better compression with ZSTD (but worse with LZ4).
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enum class Variant
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{
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Byte,
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Bit
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};
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CompressionCodecT64(TypeIndex type_idx_, Variant variant_);
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uint8_t getMethodByte() const override;
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void updateHash(SipHash & hash) const override;
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protected:
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UInt32 doCompressData(const char * src, UInt32 src_size, char * dst) const override;
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void doDecompressData(const char * src, UInt32 src_size, char * dst, UInt32 uncompressed_size) const override;
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UInt32 getMaxCompressedDataSize(UInt32 uncompressed_size) const override
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{
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/// uncompressed_size - (uncompressed_size % (sizeof(T) * 64)) + sizeof(UInt64) * sizeof(T) + header_size
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return uncompressed_size + MAX_COMPRESSED_BLOCK_SIZE + HEADER_SIZE;
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}
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bool isCompression() const override { return true; }
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bool isGenericCompression() const override { return false; }
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private:
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TypeIndex type_idx;
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Variant variant;
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};
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}
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