RtlFindSetBits function (wdm.h)

Article
02/22/2024

The RtlFindSetBits routine searches for a range of set bits of a requested size within a bitmap.

Syntax

NTSYSAPI ULONG RtlFindSetBits(
  [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 set bits will satisfy this request.

[in] HintIndex

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

Return value

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

Remarks

For a successful call, the returned bit position is not necessarily equivalent to the given HintIndex. If necessary, RtlFindSetBits searches the whole bitmap to locate a set bit range of the requested size. However, it starts searching for the requested range near HintIndex, so callers can find such a range more quickly when they can supply appropriate hints about where to start looking.

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

Requirements

Requirement	Value
Minimum supported client	Available starting with Windows 2000.
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	<= APC_LEVEL (See Remarks section)