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Performance improvement for DoubleDelta:

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* inlined getDeltaWriteSpec
 * got rid of std::singbit()
This commit is contained in:
Vasily Nemkov 2019-11-22 14:29:22 +03:00
parent b6372d40f0
commit b29ed823ed
1 changed files with 8 additions and 5 deletions
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13
dbms/src/Compression/CompressionCodecDoubleDelta.cpp
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@ -26,7 +26,7 @@ extern const int CANNOT_DECOMPRESS;
namespace
{
Int64 getMaxValueForByteSize(UInt8 byte_size)
inline Int64 getMaxValueForByteSize(Int8 byte_size)
{
switch (byte_size)
{
@ -56,6 +56,7 @@ const std::array<UInt8, 5> DELTA_SIZES{7, 9, 12, 32, 64};
template <typename T>
WriteSpec getDeltaWriteSpec(const T & value)
{
// TODO: to speed up things a bit by counting number of leading zeroes instead of doing lost of comparisons
if (value > -63 && value < 64)
{
return WriteSpec{2, 0b10, 7};
@ -107,14 +108,15 @@ UInt32 getCompressedDataSize(UInt8 data_bytes_size, UInt32 uncompressed_size)
template <typename ValueType>
UInt32 compressDataForType(const char * source, UInt32 source_size, char * dest)
{
// Since only unsinged int has granted 2-compliment overflow handling, we are doing math here on unsigned types.
// To simplify and booletproof code, we operate enforce ValueType to be unsigned too.
// Since only unsinged int has granted 2-compliment overflow handling,
// we are doing math here only on unsigned types.
// To simplify and booletproof code, we enforce ValueType to be unsigned too.
static_assert(is_unsigned_v<ValueType>, "ValueType must be unsigned.");
using UnsignedDeltaType = ValueType;
// We use signed delta type to turn huge unsigned values into smaller signed:
// ffffffff => -1
using SignedDeltaType = typename std::make_signed<UnsignedDeltaType>::type;
using SignedDeltaType = typename std::make_signed_t<UnsignedDeltaType>;
if (source_size % sizeof(ValueType) != 0)
throw Exception("Cannot compress, data size " + toString(source_size)
@ -170,7 +172,8 @@ UInt32 compressDataForType(const char * source, UInt32 source_size, char * dest)
else
{
const SignedDeltaType signed_dd = static_cast<SignedDeltaType>(double_delta);
const auto sign = std::signbit(signed_dd);
const auto sign = signed_dd < 0;
// -1 shirnks dd down to fit into number of bits, and there can't be 0, so it is OK.
const auto abs_value = static_cast<UnsignedDeltaType>(std::abs(signed_dd) - 1);
const auto write_spec = getDeltaWriteSpec(signed_dd);