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833 lines
20 KiB
C
833 lines
20 KiB
C
/*
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* PROJECT: ReactOS system libraries
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* LICENSE: GNU GPL - See COPYING in the top level directory
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* BSD - See COPYING.ARM in the top level directory
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* FILE: lib/rtl/bitmap.c
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* PURPOSE: Bitmap functions
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* PROGRAMMER: Timo Kreuzer (timo.kreuzer@reactos.org)
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*/
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/* INCLUDES *****************************************************************/
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#include <rtl.h>
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#define NDEBUG
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#include <debug.h>
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// FIXME: hack
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#undef ASSERT
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#define ASSERT(...)
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/* DATA *********************************************************************/
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/* Number of set bits per byte value */
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static const
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UCHAR
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BitCountTable[256] =
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{
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/* x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 xA xB xC xD xE xF */
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0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, /* 0x */
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, /* 1x */
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, /* 2x */
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, /* 3x */
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, /* 4x */
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, /* 5x */
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, /* 6c */
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, /* 7x */
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, /* 8x */
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, /* 9x */
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, /* Ax */
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, /* Bx */
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, /* Cx */
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, /* Dx */
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, /* Ex */
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4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8 /* Fx */
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};
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/* PRIVATE FUNCTIONS ********************************************************/
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static __inline
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ULONG
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RtlpGetLengthOfRunClear(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG StartingIndex,
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IN ULONG MaxLength)
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{
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ULONG Value, BitPos, Length;
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PULONG Buffer, MaxBuffer;
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/* Calculate positions */
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Buffer = BitMapHeader->Buffer + StartingIndex / 32;
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BitPos = StartingIndex & 31;
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/* Calculate the maximum length */
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MaxLength = min(MaxLength, BitMapHeader->SizeOfBitMap - StartingIndex);
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MaxBuffer = Buffer + (BitPos + MaxLength + 31) / 32;
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/* Clear the bits that don't belong to this run */
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Value = *Buffer++ >> BitPos << BitPos;
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/* Skip all clear ULONGs */
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while (Value == 0 && Buffer < MaxBuffer)
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{
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Value = *Buffer++;
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}
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/* Did we reach the end? */
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if (Value == 0)
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{
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/* Return maximum length */
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return MaxLength;
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}
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/* We hit a set bit, check how many clear bits are left */
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BitScanForward(&BitPos, Value);
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/* Calculate length up to where we read */
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Length = (ULONG)(Buffer - BitMapHeader->Buffer) * 32 - StartingIndex;
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Length += BitPos - 32;
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/* Make sure we don't go past the last bit */
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if (Length > BitMapHeader->SizeOfBitMap - StartingIndex)
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Length = BitMapHeader->SizeOfBitMap - StartingIndex;
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/* Return the result */
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return Length;
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}
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static __inline
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ULONG
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RtlpGetLengthOfRunSet(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG StartingIndex,
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IN ULONG MaxLength)
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{
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ULONG InvValue, BitPos, Length;
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PULONG Buffer, MaxBuffer;
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/* Calculate positions */
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Buffer = BitMapHeader->Buffer + StartingIndex / 32;
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BitPos = StartingIndex & 31;
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/* Calculate the maximum length */
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MaxLength = min(MaxLength, BitMapHeader->SizeOfBitMap - StartingIndex);
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MaxBuffer = Buffer + (BitPos + MaxLength + 31) / 32;
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/* Get the inversed value, clear bits that don't belong to the run */
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InvValue = ~(*Buffer++) >> BitPos << BitPos;
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/* Skip all set ULONGs */
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while (InvValue == 0 && Buffer < MaxBuffer)
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{
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InvValue = ~(*Buffer++);
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}
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/* Did we reach the end? */
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if (InvValue == 0)
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{
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/* Yes, return maximum */
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return MaxLength;
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}
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/* We hit a clear bit, check how many set bits are left */
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BitScanForward(&BitPos, InvValue);
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/* Calculate length up to where we read */
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Length = (ULONG)(Buffer - BitMapHeader->Buffer) * 32 - StartingIndex;
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Length += BitPos - 32;
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/* Make sure we don't go past the last bit */
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if (Length > BitMapHeader->SizeOfBitMap - StartingIndex)
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Length = BitMapHeader->SizeOfBitMap - StartingIndex;
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/* Return the result */
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return Length;
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}
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/* PUBLIC FUNCTIONS **********************************************************/
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CCHAR
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NTAPI
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RtlFindMostSignificantBit(ULONGLONG Value)
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{
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ULONG Position;
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#ifdef _M_AMD64
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if (BitScanReverse64(&Position, Value))
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{
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return (CCHAR)Position;
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}
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#else
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if (BitScanReverse(&Position, Value >> 32))
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{
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return (CCHAR)(Position + 32);
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}
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else if (BitScanReverse(&Position, (ULONG)Value))
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{
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return (CCHAR)Position;
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}
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#endif
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return -1;
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}
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CCHAR
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NTAPI
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RtlFindLeastSignificantBit(ULONGLONG Value)
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{
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ULONG Position;
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#ifdef _M_AMD64
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if (BitScanForward64(&Position, Value))
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{
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return (CCHAR)Position;
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}
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#else
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if (BitScanForward(&Position, (ULONG)Value))
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{
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return (CCHAR)Position;
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}
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else if (BitScanForward(&Position, Value >> 32))
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{
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return (CCHAR)(Position + 32);
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}
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#endif
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return -1;
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}
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VOID
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NTAPI
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RtlInitializeBitMap(
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IN PRTL_BITMAP BitMapHeader,
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IN PULONG BitMapBuffer,
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IN ULONG SizeOfBitMap)
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{
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/* Setup the bitmap header */
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BitMapHeader->SizeOfBitMap = SizeOfBitMap;
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BitMapHeader->Buffer = BitMapBuffer;
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}
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VOID
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NTAPI
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RtlClearAllBits(
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IN OUT PRTL_BITMAP BitMapHeader)
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{
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ULONG LengthInUlongs;
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LengthInUlongs = (BitMapHeader->SizeOfBitMap + 31) >> 5;
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RtlFillMemoryUlong(BitMapHeader->Buffer, LengthInUlongs << 2, 0);
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}
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VOID
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NTAPI
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RtlSetAllBits(
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IN OUT PRTL_BITMAP BitMapHeader)
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{
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ULONG LengthInUlongs;
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LengthInUlongs = (BitMapHeader->SizeOfBitMap + 31) >> 5;
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RtlFillMemoryUlong(BitMapHeader->Buffer, LengthInUlongs << 2, ~0);
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}
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VOID
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NTAPI
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RtlClearBit(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG BitNumber)
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{
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ASSERT(BitNumber <= BitMapHeader->SizeOfBitMap);
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BitMapHeader->Buffer[BitNumber >> 5] &= ~(1 << (BitNumber & 31));
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}
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VOID
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NTAPI
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RtlSetBit(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG BitNumber)
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{
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ASSERT(BitNumber <= BitMapHeader->SizeOfBitMap);
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BitMapHeader->Buffer[BitNumber >> 5] |= (1 << (BitNumber & 31));
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}
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VOID
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NTAPI
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RtlClearBits(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG StartingIndex,
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IN ULONG NumberToClear)
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{
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ULONG Bits, Mask;
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PULONG Buffer;
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ASSERT(StartingIndex + NumberToClear <= BitMapHeader->SizeOfBitMap);
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/* Calculate buffer start and first bit index */
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Buffer = &BitMapHeader->Buffer[StartingIndex >> 5];
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Bits = StartingIndex & 31;
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/* Are we unaligned? */
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if (Bits)
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{
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/* Create an inverse mask by shifting MAXULONG */
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Mask = MAXULONG << Bits;
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/* This is what's left in the first ULONG */
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Bits = 32 - Bits;
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/* Even less bits to clear? */
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if (NumberToClear < Bits)
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{
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/* Calculate how many bits are left */
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Bits -= NumberToClear;
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/* Fixup the mask on the high side */
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Mask = Mask << Bits >> Bits;
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/* Clear bits and return */
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*Buffer &= ~Mask;
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return;
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}
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/* Clear bits */
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*Buffer &= ~Mask;
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/* Update buffer and left bits */
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Buffer++;
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NumberToClear -= Bits;
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}
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/* Clear all full ULONGs */
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RtlFillMemoryUlong(Buffer, NumberToClear >> 3, 0);
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Buffer += NumberToClear >> 5;
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/* Clear what's left */
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NumberToClear &= 31;
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Mask = MAXULONG << NumberToClear;
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*Buffer &= Mask;
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}
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VOID
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NTAPI
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RtlSetBits(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG StartingIndex,
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IN ULONG NumberToSet)
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{
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ULONG Bits, Mask;
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PULONG Buffer;
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ASSERT(StartingIndex + NumberToSet <= BitMapHeader->SizeOfBitMap);
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/* Calculate buffer start and first bit index */
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Buffer = &BitMapHeader->Buffer[StartingIndex >> 5];
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Bits = StartingIndex & 31;
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/* Are we unaligned? */
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if (Bits)
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{
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/* Create a mask by shifting MAXULONG */
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Mask = MAXULONG << Bits;
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/* This is what's left in the first ULONG */
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Bits = 32 - Bits;
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/* Even less bits to clear? */
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if (NumberToSet < Bits)
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{
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/* Calculate how many bits are left */
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Bits -= NumberToSet;
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/* Fixup the mask on the high side */
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Mask = Mask << Bits >> Bits;
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/* Set bits and return */
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*Buffer |= Mask;
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return;
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}
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/* Set bits */
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*Buffer |= Mask;
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/* Update buffer and left bits */
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Buffer++;
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NumberToSet -= Bits;
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}
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/* Set all full ULONGs */
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RtlFillMemoryUlong(Buffer, NumberToSet >> 3, MAXULONG);
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Buffer += NumberToSet >> 5;
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/* Set what's left */
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NumberToSet &= 31;
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Mask = MAXULONG << NumberToSet;
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*Buffer |= ~Mask;
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}
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BOOLEAN
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NTAPI
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RtlTestBit(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG BitNumber)
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{
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ASSERT(BitNumber < BitMapHeader->SizeOfBitMap);
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return (BitMapHeader->Buffer[BitNumber >> 5] >> (BitNumber & 31)) & 1;
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}
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BOOLEAN
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NTAPI
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RtlAreBitsClear(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG StartingIndex,
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IN ULONG Length)
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{
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/* Verify parameters */
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if ((StartingIndex + Length > BitMapHeader->SizeOfBitMap) ||
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(StartingIndex + Length <= StartingIndex))
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return FALSE;
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return RtlpGetLengthOfRunClear(BitMapHeader, StartingIndex, Length) >= Length;
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}
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BOOLEAN
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NTAPI
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RtlAreBitsSet(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG StartingIndex,
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IN ULONG Length)
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{
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/* Verify parameters */
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if ((StartingIndex + Length > BitMapHeader->SizeOfBitMap) ||
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(StartingIndex + Length <= StartingIndex))
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return FALSE;
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return RtlpGetLengthOfRunSet(BitMapHeader, StartingIndex, Length) >= Length;
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}
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ULONG
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NTAPI
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RtlNumberOfSetBits(
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IN PRTL_BITMAP BitMapHeader)
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{
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PUCHAR Byte, MaxByte;
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ULONG BitCount = 0, Shift;
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Byte = (PUCHAR)BitMapHeader->Buffer;
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MaxByte = Byte + BitMapHeader->SizeOfBitMap / 8;
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while (Byte < MaxByte)
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{
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BitCount += BitCountTable[*Byte++];
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}
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Shift = 8 - (BitMapHeader->SizeOfBitMap & 7);
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BitCount += BitCountTable[((*Byte) << Shift) & 0xFF];
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return BitCount;
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}
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ULONG
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NTAPI
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RtlNumberOfClearBits(
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IN PRTL_BITMAP BitMapHeader)
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{
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/* Do some math */
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return BitMapHeader->SizeOfBitMap - RtlNumberOfSetBits(BitMapHeader);
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}
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ULONG
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NTAPI
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RtlFindClearBits(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG NumberToFind,
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IN ULONG HintIndex)
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{
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ULONG CurrentBit, Margin, CurrentLength;
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/* Check for valid parameters */
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if (!BitMapHeader || NumberToFind > BitMapHeader->SizeOfBitMap)
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{
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return MAXULONG;
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}
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/* Check if the hint is outside the bitmap */
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if (HintIndex >= BitMapHeader->SizeOfBitMap) HintIndex = 0;
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/* Check for trivial case */
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if (NumberToFind == 0)
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{
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/* Return hint rounded down to byte margin */
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return HintIndex & ~7;
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}
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/* First margin is end of bitmap */
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Margin = BitMapHeader->SizeOfBitMap;
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retry:
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/* Start with hint index, length is 0 */
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CurrentBit = HintIndex;
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/* Loop until something is found or the end is reached */
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while (CurrentBit + NumberToFind < Margin)
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{
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/* Search for the next clear run, by skipping a set run */
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CurrentBit += RtlpGetLengthOfRunSet(BitMapHeader,
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CurrentBit,
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MAXULONG);
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/* Get length of the clear bit run */
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CurrentLength = RtlpGetLengthOfRunClear(BitMapHeader,
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CurrentBit,
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NumberToFind);
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/* Is this long enough? */
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if (CurrentLength >= NumberToFind)
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{
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/* It is */
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return CurrentBit;
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}
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CurrentBit += CurrentLength;
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}
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/* Did we start at a hint? */
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if (HintIndex)
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{
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/* Retry at the start */
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Margin = min(HintIndex + NumberToFind, BitMapHeader->SizeOfBitMap);
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HintIndex = 0;
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goto retry;
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}
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/* Nothing found */
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return MAXULONG;
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}
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ULONG
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NTAPI
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RtlFindSetBits(
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IN PRTL_BITMAP BitMapHeader,
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IN ULONG NumberToFind,
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IN ULONG HintIndex)
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{
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ULONG CurrentBit, Margin, CurrentLength;
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/* Check for valid parameters */
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if (!BitMapHeader || NumberToFind > BitMapHeader->SizeOfBitMap)
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{
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return MAXULONG;
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}
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/* Check if the hint is outside the bitmap */
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if (HintIndex >= BitMapHeader->SizeOfBitMap) HintIndex = 0;
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/* Check for trivial case */
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if (NumberToFind == 0)
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{
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/* Return hint rounded down to byte margin */
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return HintIndex & ~7;
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}
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/* First margin is end of bitmap */
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Margin = BitMapHeader->SizeOfBitMap;
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retry:
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/* Start with hint index, length is 0 */
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CurrentBit = HintIndex;
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/* Loop until something is found or the end is reached */
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while (CurrentBit + NumberToFind <= Margin)
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{
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/* Search for the next set run, by skipping a clear run */
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CurrentBit += RtlpGetLengthOfRunClear(BitMapHeader,
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CurrentBit,
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MAXULONG);
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/* Get length of the set bit run */
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CurrentLength = RtlpGetLengthOfRunSet(BitMapHeader,
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CurrentBit,
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NumberToFind);
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/* Is this long enough? */
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if (CurrentLength >= NumberToFind)
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{
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/* It is */
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return CurrentBit;
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}
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CurrentBit += CurrentLength;
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}
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/* Did we start at a hint? */
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if (HintIndex)
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{
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/* Retry at the start */
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Margin = min(HintIndex + NumberToFind, BitMapHeader->SizeOfBitMap);
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HintIndex = 0;
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goto retry;
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}
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/* Nothing found */
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return MAXULONG;
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}
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ULONG
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NTAPI
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|
RtlFindClearBitsAndSet(
|
|
PRTL_BITMAP BitMapHeader,
|
|
ULONG NumberToFind,
|
|
ULONG HintIndex)
|
|
{
|
|
ULONG Position;
|
|
|
|
/* Try to find clear bits */
|
|
Position = RtlFindClearBits(BitMapHeader, NumberToFind, HintIndex);
|
|
|
|
/* Did we get something? */
|
|
if (Position != MAXULONG)
|
|
{
|
|
/* Yes, set the bits */
|
|
RtlSetBits(BitMapHeader, Position, NumberToFind);
|
|
}
|
|
|
|
/* Return what we found */
|
|
return Position;
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindSetBitsAndClear(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN ULONG NumberToFind,
|
|
IN ULONG HintIndex)
|
|
{
|
|
ULONG Position;
|
|
|
|
/* Try to find set bits */
|
|
Position = RtlFindSetBits(BitMapHeader, NumberToFind, HintIndex);
|
|
|
|
/* Did we get something? */
|
|
if (Position != MAXULONG)
|
|
{
|
|
/* Yes, clear the bits */
|
|
RtlClearBits(BitMapHeader, Position, NumberToFind);
|
|
}
|
|
|
|
/* Return what we found */
|
|
return Position;
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindNextForwardRunClear(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN ULONG FromIndex,
|
|
IN PULONG StartingRunIndex)
|
|
{
|
|
ULONG Length;
|
|
|
|
/* Check for buffer overrun */
|
|
if (FromIndex >= BitMapHeader->SizeOfBitMap)
|
|
{
|
|
*StartingRunIndex = FromIndex;
|
|
return 0;
|
|
}
|
|
|
|
/* Assume a set run first, count it's length */
|
|
Length = RtlpGetLengthOfRunSet(BitMapHeader, FromIndex, MAXULONG);
|
|
*StartingRunIndex = FromIndex + Length;
|
|
|
|
/* Now return the length of the run */
|
|
return RtlpGetLengthOfRunClear(BitMapHeader, FromIndex + Length, MAXULONG);
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindNextForwardRunSet(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN ULONG FromIndex,
|
|
IN PULONG StartingRunIndex)
|
|
{
|
|
ULONG Length;
|
|
|
|
/* Check for buffer overrun */
|
|
if (FromIndex >= BitMapHeader->SizeOfBitMap)
|
|
{
|
|
*StartingRunIndex = FromIndex;
|
|
return 0;
|
|
}
|
|
|
|
/* Assume a clear run first, count it's length */
|
|
Length = RtlpGetLengthOfRunClear(BitMapHeader, FromIndex, MAXULONG);
|
|
*StartingRunIndex = FromIndex + Length;
|
|
|
|
/* Now return the length of the run */
|
|
return RtlpGetLengthOfRunSet(BitMapHeader, FromIndex, MAXULONG);
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindFirstRunClear(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN PULONG StartingIndex)
|
|
{
|
|
return RtlFindNextForwardRunClear(BitMapHeader, 0, StartingIndex);
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindLastBackwardRunClear(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN ULONG FromIndex,
|
|
IN PULONG StartingRunIndex)
|
|
{
|
|
UNIMPLEMENTED;
|
|
return 0;
|
|
}
|
|
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindClearRuns(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN PRTL_BITMAP_RUN RunArray,
|
|
IN ULONG SizeOfRunArray,
|
|
IN BOOLEAN LocateLongestRuns)
|
|
{
|
|
ULONG StartingIndex, NumberOfBits, Run, FromIndex = 0, SmallestRun = 0;
|
|
|
|
/* Loop the runs */
|
|
for (Run = 0; Run < SizeOfRunArray; Run++)
|
|
{
|
|
/* Look for a run */
|
|
NumberOfBits = RtlFindNextForwardRunClear(BitMapHeader,
|
|
FromIndex,
|
|
&StartingIndex);
|
|
|
|
/* Nothing more found? Quit looping. */
|
|
if (NumberOfBits == 0) break;
|
|
|
|
/* Add another run */
|
|
RunArray[Run].StartingIndex = StartingIndex;
|
|
RunArray[Run].NumberOfBits = NumberOfBits;
|
|
|
|
/* Update smallest run */
|
|
if (NumberOfBits < RunArray[SmallestRun].NumberOfBits)
|
|
{
|
|
SmallestRun = Run;
|
|
}
|
|
|
|
/* Advance bits */
|
|
FromIndex = StartingIndex + NumberOfBits;
|
|
}
|
|
|
|
/* Check if we are finished */
|
|
if (Run < SizeOfRunArray || !LocateLongestRuns)
|
|
{
|
|
/* Return the number of found runs */
|
|
return Run;
|
|
}
|
|
|
|
while (1)
|
|
{
|
|
/* Look for a run */
|
|
NumberOfBits = RtlFindNextForwardRunClear(BitMapHeader,
|
|
FromIndex,
|
|
&StartingIndex);
|
|
|
|
/* Nothing more found? Quit looping. */
|
|
if (NumberOfBits == 0) break;
|
|
|
|
/* Check if we have something to update */
|
|
if (NumberOfBits > RunArray[SmallestRun].NumberOfBits)
|
|
{
|
|
/* Update smallest run */
|
|
RunArray[SmallestRun].StartingIndex = StartingIndex;
|
|
RunArray[SmallestRun].NumberOfBits = NumberOfBits;
|
|
|
|
/* Loop all runs */
|
|
for (Run = 0; Run < SizeOfRunArray; Run++)
|
|
{
|
|
/*Is this the new smallest run? */
|
|
if (NumberOfBits < RunArray[SmallestRun].NumberOfBits)
|
|
{
|
|
/* Set it as new smallest run */
|
|
SmallestRun = Run;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Advance bits */
|
|
FromIndex += NumberOfBits;
|
|
}
|
|
|
|
return Run;
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindLongestRunClear(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN PULONG StartingIndex)
|
|
{
|
|
ULONG NumberOfBits, Index, MaxNumberOfBits = 0, FromIndex = 0;
|
|
|
|
while (1)
|
|
{
|
|
/* Look for a run */
|
|
NumberOfBits = RtlFindNextForwardRunClear(BitMapHeader,
|
|
FromIndex,
|
|
&Index);
|
|
|
|
/* Nothing more found? Quit looping. */
|
|
if (NumberOfBits == 0) break;
|
|
|
|
/* Was that the longest run? */
|
|
if (NumberOfBits > MaxNumberOfBits)
|
|
{
|
|
/* Update values */
|
|
MaxNumberOfBits = NumberOfBits;
|
|
*StartingIndex = Index;
|
|
}
|
|
|
|
/* Advance bits */
|
|
FromIndex += NumberOfBits;
|
|
}
|
|
|
|
return MaxNumberOfBits;
|
|
}
|
|
|
|
ULONG
|
|
NTAPI
|
|
RtlFindLongestRunSet(
|
|
IN PRTL_BITMAP BitMapHeader,
|
|
IN PULONG StartingIndex)
|
|
{
|
|
ULONG NumberOfBits, Index, MaxNumberOfBits = 0, FromIndex = 0;
|
|
|
|
while (1)
|
|
{
|
|
/* Look for a run */
|
|
NumberOfBits = RtlFindNextForwardRunSet(BitMapHeader,
|
|
FromIndex,
|
|
&Index);
|
|
|
|
/* Nothing more found? Quit looping. */
|
|
if (NumberOfBits == 0) break;
|
|
|
|
/* Was that the longest run? */
|
|
if (NumberOfBits > MaxNumberOfBits)
|
|
{
|
|
/* Update values */
|
|
MaxNumberOfBits = NumberOfBits;
|
|
*StartingIndex = Index;
|
|
}
|
|
|
|
/* Advance bits */
|
|
FromIndex += NumberOfBits;
|
|
}
|
|
|
|
return MaxNumberOfBits;
|
|
}
|
|
|