RtlReserveChunk - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H

NTSYSAPI
NTSTATUS
NTAPI
RtlReserveChunk(
    _In_ USHORT CompressionFormat,
    _Inout_ PUCHAR *CompressedBuffer,
    _In_ PUCHAR EndOfCompressedBufferPlus1,
    _Out_ PUCHAR *ChunkBuffer,
    _In_ ULONG ChunkSize
    );

#endif

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This function is documented in Windows Driver Kit.