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CompressedWriteBuffer added comment

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This commit is contained in:
Maksim Kita 2022-05-23 12:09:44 +02:00
parent 692c19b80d
commit 3a22d8ef2c
1 changed files with 11 additions and 4 deletions
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15
src/Compression/CompressedWriteBuffer.cpp
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@ -22,15 +22,22 @@ void CompressedWriteBuffer::nextImpl()
if (!offset())
return;
UInt32 compressed_size = 0;
size_t decompressed_size = offset();
UInt32 compressed_reserve_size = codec->getCompressedReserveSize(decompressed_size);
if (out.available() > compressed_reserve_size + CHECKSUM_SIZE)
/** During compression we need buffer with capacity >= compressed_reserve_size + CHECKSUM_SIZE.
*
* If output buffer has necessary capacity, we can compress data directly in output buffer.
* Then we can write checksum at the output buffer begin.
*
* If output buffer does not have necessary capacity. Compress data in temporary buffer.
* Then we can write checksum and temporary buffer in output buffer.
*/
if (out.available() >= compressed_reserve_size + CHECKSUM_SIZE)
{
char * out_checksum_ptr = out.position();
char * out_compressed_ptr = out.position() + CHECKSUM_SIZE;
compressed_size = codec->compress(working_buffer.begin(), decompressed_size, out_compressed_ptr);
UInt32 compressed_size = codec->compress(working_buffer.begin(), decompressed_size, out_compressed_ptr);
CityHash_v1_0_2::uint128 checksum = CityHash_v1_0_2::CityHash128(out_compressed_ptr, compressed_size);
memcpy(out_checksum_ptr, reinterpret_cast<const char *>(&checksum), CHECKSUM_SIZE);
@ -39,7 +46,7 @@ void CompressedWriteBuffer::nextImpl()
else
{
compressed_buffer.resize(compressed_reserve_size);
compressed_size = codec->compress(working_buffer.begin(), decompressed_size, compressed_buffer.data());
UInt32 compressed_size = codec->compress(working_buffer.begin(), decompressed_size, compressed_buffer.data());
CityHash_v1_0_2::uint128 checksum = CityHash_v1_0_2::CityHash128(compressed_buffer.data(), compressed_size);
out.write(reinterpret_cast<const char *>(&checksum), CHECKSUM_SIZE);