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RtlGetCompressionWorkSpaceSize function

The RtlGetCompressionWorkSpaceSize function is used to determine the correct size of the WorkSpace buffer for the RtlCompressBuffer and RtlDecompressFragment functions.

Syntax

Copy

NTSTATUS RtlGetCompressionWorkSpaceSize(
  __in   USHORT CompressionFormatAndEngine,
  __out  PULONG CompressBufferWorkSpaceSize,
  __out  PULONG CompressFragmentWorkSpaceSize
);

Parameters

CompressionFormatAndEngine [in]

Bitmask specifying the compression format and engine type. This parameter must be set to one of the following bitwise OR combinations:

COMPRESSION_FORMAT_LZNT1 | COMPRESSION_ENGINE_STANDARD
COMPRESSION_FORMAT_LZNT1 | COMPRESSION_ENGINE_MAXIMUM

The meanings of these, and other related values, are as follows:

Value	Meaning
COMPRESSION_FORMAT_NONE	Not supported by this function.
COMPRESSION_FORMAT_DEFAULT	Not supported by this function.
COMPRESSION_FORMAT_LZNT1	Specifies that compression should be performed. This value is required.
COMPRESSION_ENGINE_STANDARD	Data is compressed using an algorithm which provides a balance between data compression and performance. This value cannot be used with COMPRESSION_ENGINE_MAXIMUM.
COMPRESSION_ENGINE_MAXIMUM	Data is compressed using an algorithm which provides maximum data compression but with relatively slower performance. This value cannot be used with COMPRESSION_ENGINE_STANDARD.
COMPRESSION_ENGINE_HIBER	Not supported by this function.

CompressBufferWorkSpaceSize [out]

A pointer to a caller-allocated buffer receiving the size, in bytes, required to compress a buffer. This value is used to determine the correct size of RtlCompressBuffer's WorkSpace buffer.

CompressFragmentWorkSpaceSize [out]

A pointer to a caller-allocated buffer receiving the size, in bytes, required to decompress a compressed buffer to a fragment. This value is used to determine the correct size of RtlDecompressFragment's WorkSpace buffer. Note that the RtlCompressFragment function does not currently exist.

Return value

RtlGetCompressionWorkSpaceSizereturns an appropriate error status, such as one of the following:

Return code	Description
STATUS_SUCCESS	The required buffer sizes, in bytes, were successfully returned.
STATUS_INVALID_PARAMETER	An invalid compression format was specified via the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is either COMPRESSION_FORMAT_NONE or COMPRESSION_FORMAT_DEFAULT (but not both), this value is returned.
STATUS_UNSUPPORTED_COMPRESSION	An invalid compression format was specified via the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is not one of the following, STATUS_UNSUPPORTED_COMPRESSION is returned: COMPRESSION_FORMAT_LZNT1 COMPRESSION_FORMAT_NONE (in this case, STATUS_INVALID_PARAMETER is returned) COMPRESSION_FORMAT_DEFAULT (in this case, STATUS_INVALID_PARAMETER is returned)
STATUS_NOT_SUPPORTED	An invalid compression engine was specified via the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is not COMPRESSION_ENGINE_STANDARD or COMPRESSION_ENGINE_MAXIMUM (but not both), this value is returned.

Remarks

The RtlCompressBuffer and RtlDecompressFragmentfunctions require an appropriately sized work space buffer to compress and decompress successfully. To determine the correct work space buffer size, in bytes, call the RtlGetCompressionWorkSpaceSize function.

As an example, the WorkSpace parameter of the RtlCompressBuffer function must point to an adequately sized work space buffer. The CompressBufferWorkSpaceSize parameter of the RtlGetCompressionWorkSpaceSize provides this size.

To compress an uncompressed buffer, use the RtlCompressBuffer function.

To decompress a compressed buffer, use the RtlDecompressBuffer function.

To decompress only a portion of a compressed buffer (that is, a "fragment" of the buffer), use the RtlDecompressFragment function.

Requirements