1#pragma once
2
3#include <Core/Types.h>
4#include <Compression/ICompressionCodec.h>
5
6namespace DB
7{
8
9/// Get 64 integer valuses, makes 64x64 bit matrix, transpose it and crop unused bits (most significant zeroes).
10/// In example, if we have UInt8 with only 0 and 1 inside 64xUInt8 would be compressed into 1xUInt64.
11/// It detects unused bits by calculating min and max values of data part, saving them in header in compression phase.
12/// There's a special case with signed integers parts with crossing zero data. Here it stores one more bit to detect sign of value.
13class CompressionCodecT64 : public ICompressionCodec
14{
15public:
16 static constexpr UInt32 HEADER_SIZE = 1 + 2 * sizeof(UInt64);
17 static constexpr UInt32 MAX_COMPRESSED_BLOCK_SIZE = sizeof(UInt64) * 64;
18
19 /// There're 2 compression variants:
20 /// Byte - transpose bit matrix by bytes (only the last not full byte is transposed by bits). It's default.
21 /// Bits - full bit-transpose of the bit matrix. It uses more resources and leads to better compression with ZSTD (but worse with LZ4).
22 enum class Variant
23 {
24 Byte,
25 Bit
26 };
27
28 CompressionCodecT64(TypeIndex type_idx_, Variant variant_)
29 : type_idx(type_idx_)
30 , variant(variant_)
31 {}
32
33 UInt8 getMethodByte() const override;
34 String getCodecDesc() const override
35 {
36 return String("T64") + ((variant == Variant::Byte) ? "" : "(\'bit\')");
37 }
38
39 void useInfoAboutType(DataTypePtr data_type) override;
40
41protected:
42 UInt32 doCompressData(const char * source, UInt32 source_size, char * dest) const override;
43 void doDecompressData(const char * source, UInt32 source_size, char * dest, UInt32 uncompressed_size) const override;
44
45 UInt32 getMaxCompressedDataSize(UInt32 uncompressed_size) const override
46 {
47 /// uncompressed_size - (uncompressed_size % (sizeof(T) * 64)) + sizeof(UInt64) * sizeof(T) + header_size
48 return uncompressed_size + MAX_COMPRESSED_BLOCK_SIZE + HEADER_SIZE;
49 }
50
51private:
52 TypeIndex type_idx;
53 Variant variant;
54};
55
56class CompressionCodecFactory;
57void registerCodecT64(CompressionCodecFactory & factory);
58
59}
60