bitmask.c

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/*
 * Copyright (c) 2020 Bitdefender
 * SPDX-License-Identifier: Apache-2.0
 */
#include "bitmask.h"
#include "glue.h"
#include "introcrt.h"


static inline
UINT64 *
BitMaskGetBaseAndBit(
    _In_ BITMASK *BitMask,
    _Inout_ DWORD *BitPos
    )
{
    UINT64 *b = (UINT64 *)BitMask->Bits + (*BitPos / 64);

    *BitPos %= 64;

    return b;
}


static inline
UINT64 *
BitMaskGetBase(
    _In_ BITMASK *BitMask,
    _In_ DWORD BitPos
    )
{
    return (UINT64 *)BitMask->Bits + (BitPos / 64);
}


BITMASK *
BitMaskAlloc(
    _In_ size_t Size
    )
{
    BITMASK *bitmask = HpAllocWithTag(sizeof(*bitmask) + (Size / 8) + (Size % 8 != 0), IC_TAG_ALLOC);
    if (NULL == bitmask)
    {
        return NULL;
    }

    bitmask->Length = Size;

    return bitmask;
}


void
BitMaskFree(
    _Inout_ BITMASK **BitMask
    )
{
    HpFreeAndNullWithTag(BitMask, IC_TAG_ALLOC);
}


void
BitMaskSet(
    _Inout_ BITMASK *BitMask,
    _In_ DWORD BitPos
    )
{
    if (BitPos > BitMask->Length)
    {
        ERROR("[ERROR] Trying to set bit %u which is outside of the bitmask (%zu length)\n",
              BitPos, BitMask->Length);
        return;
    }

    UINT64 *bitBase = BitMaskGetBaseAndBit(BitMask, &BitPos);

    *bitBase |= (1ull << BitPos);
}


void
BitMaskClear(
    _Inout_ BITMASK *BitMask,
    _In_ DWORD BitPos
    )
{
    if (BitPos > BitMask->Length)
    {
        ERROR("[ERROR] Trying to set bit %u which is outside of the bitmask (%zu length)\n",
              BitPos, BitMask->Length);
        return;
    }

    UINT64 *bitBase = BitMaskGetBaseAndBit(BitMask, &BitPos);

    *bitBase &= ~(1ull << BitPos);
}


BYTE
BitMaskTest(
    _In_ BITMASK *BitMask,
    _In_ DWORD BitPos
    )
{
    if (BitPos > BitMask->Length)
    {
        ERROR("[ERROR] Trying to set bit %u which is outside of the bitmask (%zu length)\n",
              BitPos, BitMask->Length);
        return 0;
    }

    UINT64 *bitBase = BitMaskGetBaseAndBit(BitMask, &BitPos);

    return (*bitBase >> BitPos) & 1;
}


BYTE
BitMaskTestAndSet(
    _Inout_ BITMASK *BitMask,
    _In_ DWORD BitPos
    )
{
    if (BitPos > BitMask->Length)
    {
        ERROR("[ERROR] Trying to set bit %u which is outside of the bitmask (%zu length)\n",
              BitPos, BitMask->Length);
        return 0;
    }

    UINT64 *bitBase = BitMaskGetBaseAndBit(BitMask, &BitPos);

    BYTE old = (*bitBase >> BitPos) & 1;

    *bitBase |= (1ull << BitPos);

    return old;
}


BYTE
BitMaskTestAndReset(
    _Inout_ BITMASK *BitMask,
    _In_ DWORD BitPos
    )
{
    if (BitPos > BitMask->Length)
    {
        ERROR("[ERROR] Trying to set bit %u which is outside of the bitmask (%zu length)\n",
              BitPos, BitMask->Length);

        return 0;
    }

    UINT64 *bitBase = BitMaskGetBaseAndBit(BitMask, &BitPos);

    BYTE old = (*bitBase >> BitPos) & 1;

    *bitBase &= ~(1ull << BitPos);

    return old;
}


DWORD
BitMaskScanForward(
    _In_ BITMASK *BitMask
    )
{
    DWORD index = 0;

    for (DWORD i = 0; i < BitMask->Length; i += 64)
    {
        UINT64 base = *BitMaskGetBase(BitMask, i);

        if (!_BitScanForward64(&index, ~base))
        {
            continue;
        }

        return i + index;
    }

    return (DWORD) -1;
}