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RtlFindLastBackwardRunClear routine

The RtlFindLastBackwardRunClear routine searches a given bitmap for the preceding clear run of bits, starting from the specified index position.

Syntax


ULONG RtlFindLastBackwardRunClear(
  _In_   PRTL_BITMAP BitMapHeader,
  _In_   ULONG FromIndex,
  _Out_  PULONG StartingRunIndex
);

Parameters

BitMapHeader [in]

A pointer to the RTL_BITMAP structure that describes the bitmap. This structure must have been initialized by the RtlInitializeBitMap routine.

FromIndex [in]

Specifies a zero-based bit position at which to start looking for a clear run of bits.

StartingRunIndex [out]

Pointer to a variable in which the starting index of the clear run found in the bitmap is returned. This is a zero-based value indicating the bit position of the first clear bit in the run preceding the given FromIndex. Its value is meaningless if RtlFindLastBackwardRunClear cannot find a run of clear bits.

Return value

RtlFindLastBackwardRunClear returns the number of bits in the run beginning at StartingRunIndex, or zero if it cannot find a run of clear bits preceding FromIndex in the bitmap.

Remarks

On checked builds of Windows Vista and earlier versions of Windows, the internal implementation of the RtlFindLastBackwardRunClear routine can fail a bogus assertion if the caller is running at IRQL = DISPATCH_LEVEL. The failure of this assertion is harmless and can safely be ignored.

Callers of RtlFindLastBackwardRunClear must be running at IRQL <= APC_LEVEL if the memory that contains the bitmap variable is pageable or the memory at BitMapHeader is pageable. Otherwise, RtlFindLastBackwardRunClear can be called at any IRQL.

Requirements

Version

Available starting with Windows 2000.

Header

Wdm.h (include Wdm.h, Ntddk.h, or Ntifs.h)

Library

Ntoskrnl.lib

IRQL

<= APC_LEVEL (see Remarks section)

See also

RtlAreBitsClear
RTL_BITMAP
RtlFindClearBits
RtlFindClearRuns
RtlFindFirstRunClear
RtlFindLastBackwardRunClear
RtlFindLongestRunClear
RtlFindNextForwardRunClear
RtlInitializeBitMap

 

 

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