RtlFindClearBits function (wdm.h)

Article
01/13/2023

The RtlFindClearBits routine searches for a range of clear bits of a requested size within a bitmap.

Syntax

NTSYSAPI ULONG RtlFindClearBits(
  [in] PRTL_BITMAP BitMapHeader,
  [in] ULONG       NumberToFind,
  [in] ULONG       HintIndex
);

Parameters

[in] BitMapHeader

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

[in] NumberToFind

Specifies how many contiguous clear bits will satisfy this request.

[in] HintIndex

Specifies a zero-based bit position from which to start looking for a clear bit range of the given size.

Return value

RtlFindClearBits either returns the zero-based starting bit index for a clear bit range of at least the requested size, or it returns 0xFFFFFFFF if it cannot find such a range within the given bitmap.

Remarks

For a successful call, the returned bit position is not necessarily equivalent to the given HintIndex. If necessary, RtlFindClearBits searches the whole bitmap to locate a clear bit range of the requested size. Callers can find such a range more quickly when they can supply appropriate hints about where to start looking.

If a matching range is not found between the hint index and the end of the bitmap, RtlFindClearBits continues searching from the beginning of the bitmap back to the hint index.

If you only want an index returned that is greater than or equal to some value, use RtlFindNextForwardRunClear instead.

Callers of RtlFindClearBits 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, RtlFindClearBits can be called at any IRQL.

Requirements

Requirement	Value
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	IRQL <= APC_LEVEL (See Remarks section)