RtlFindClearRuns - NtDoc

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

NTSYSAPI
ULONG
NTAPI
RtlFindClearRuns(
    _In_ PRTL_BITMAP BitMapHeader,
    _Out_writes_to_(SizeOfRunArray, return) PRTL_BITMAP_RUN RunArray,
    _In_range_(>, 0) ULONG SizeOfRunArray,
    _In_ BOOLEAN LocateLongestRuns
    );

#endif

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This function is documented in Windows Driver Kit.