LARGE_INTEGER NTAPI INIT_FUNCTION KiComputeReciprocal	(	IN LONG	Divisor,
		OUT PUCHAR	Shift
	)

Definition at line 123 of file krnlinit.c.

Referenced by KiInitializeKernel().

{
    LARGE_INTEGER Reciprocal = {{0, 0}};
    LONG BitCount = 0, Remainder = 1;

    /* Start by calculating the remainder */
    while (Reciprocal.HighPart >= 0)
    {
        /* Increase the loop (bit) count */
        BitCount++;

        /* Calculate the current fraction */
        Reciprocal.HighPart = (Reciprocal.HighPart << 1) |
                              (Reciprocal.LowPart >> 31);
        Reciprocal.LowPart <<= 1;

        /* Double the remainder and see if we went past the divisor */
        Remainder <<= 1;
        if (Remainder >= Divisor)
        {
            /* Set the low-bit and calculate the new remainder */
            Remainder -= Divisor;
            Reciprocal.LowPart |= 1;
        }
    }

    /* Check if we have a remainder */
    if (Remainder)
    {
        /* Check if the current fraction value is too large */
        if ((Reciprocal.LowPart == 0xFFFFFFFF) &&
            (Reciprocal.HighPart == (LONG)0xFFFFFFFF))
        {
            /* Set the high bit and reduce the bit count */
            Reciprocal.LowPart = 0;
            Reciprocal.HighPart = 0x80000000;
            BitCount--;
        }
        else
        {
            /* Check if only the lowest bits got too large */
            if (Reciprocal.LowPart == 0xFFFFFFFF)
            {
                /* Reset them and increase the high bits instead */
                Reciprocal.LowPart = 0;
                Reciprocal.HighPart++;
            }
            else
            {
                /* All is well, increase the low bits */
                Reciprocal.LowPart++;
            }
        }
    }

    /* Now calculate the actual shift and return the reciprocal */
    *Shift = (UCHAR)BitCount - 64;
    return Reciprocal;
}

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