/**
 * PROJECT:         ExectOS
 * COPYRIGHT:       See COPYING.md in the top level directory
 * FILE:            xtoskrnl/rtl/memory.cc
 * DESCRIPTION:     Memory related routines
 * DEVELOPERS:      Rafal Kupiec <belliash@codingworkshop.eu.org>
 */

#include <xtos.hh>


/**
 * This routine compares the first bytes of the specified memory buffers.
 *
 * @param LeftBuffer
 *        Supplies a pointer to the first block of memory to compare.
 *
 * @param RightBuffer
 *        Supplies a pointer to the second block of memory to compare.
 *
 * @param Length
 *        Specifies a number of bytes to compare.
 *
 * @return This routine returns a number of bytes that are equal in both memory blocks.
 *
 * @since NT 3.5
 */
XTAPI
SIZE_T
RTL::Memory::CompareMemory(IN PCVOID LeftBuffer,
                           IN PCVOID RightBuffer,
                           IN SIZE_T Length)
{
    SIZE_T Bytes = 0;

    /* Check if there is anything to compare */
    if(Length)
    {
        /* Iterate through whole buffer length */
        while(Bytes < Length)
        {
            /* Compare bytes from both bufers */
            if(((CONST PBYTE)LeftBuffer)[Bytes] != ((CONST PBYTE)RightBuffer)[Bytes])
            {
                /* Buffers are different */
                break;
            }

            /* Increase number of common bytes */
            Bytes++;
        }
    }

    /* Return number of equal characters */
    return Bytes;
}

/**
 * Copies a block of memory from a source buffer to a destination buffer.
 *
 * @param Destination
 *        Supplies a pointer to the target buffer where the data will be copied.
 *
 * @param Source
 *        Supplies a pointer to the source buffer containing the data to copy.
 *
 * @param Length
 *        Specifies the number of bytes to transfer.
 *
 * @return This routine does not return any value.
 *
 * @since NT 3.5
 */
XTAPI
VOID
RTL::Memory::CopyMemory(OUT PVOID Destination,
                        IN PCVOID Source,
                        IN SIZE_T Length)
{
    ULONG_PTR BytesToAlign, DestinationPointer, Remainder, SourcePointer, WordCount;
    PULONG_PTR DestinationWord, SourceWord;
    PCHAR DestinationByte, SourceByte;

    /* Check if the payload is empty or the buffers are identical */
    if(Length == 0 || Destination == Source)
    {
        /* No operation is required */
        return;
    }

    /* Cast the pointers to scalar values */
    DestinationPointer = (ULONG_PTR)Destination;
    SourcePointer = (ULONG_PTR)Source;

    /* Check if the destination overlaps the source in a destructive manner */
    if(SourcePointer < DestinationPointer && DestinationPointer < (SourcePointer + Length))
    {
        /* Initialize the pointers for a backward traversal */
        DestinationByte = (PCHAR)(DestinationPointer + Length);
        SourceByte = (PCHAR)(SourcePointer + Length);

        /* Calculate the number of trailing bytes */
        BytesToAlign = ((ULONG_PTR)DestinationByte) & (sizeof(ULONG_PTR) - 1);
        if(BytesToAlign > Length)
        {
            /* Clamp the alignment requirement */
            BytesToAlign = Length;
        }

        /* Compute the alignment byte count from the remaining payload */
        Length -= BytesToAlign;

        /* Sequentially copy the unaligned trailing bytes */
        while(BytesToAlign--)
        {
            /* Transfer a single byte */
            *(--DestinationByte) = *(--SourceByte);
        }

        /* Compute the number of full words and any leftover */
        WordCount = Length / sizeof(ULONG_PTR);
        Remainder = Length & (sizeof(ULONG_PTR) - 1);

        /* Elevate the byte pointers to word pointers */
        DestinationWord = (PULONG_PTR)DestinationByte;
        SourceWord = (PULONG_PTR)SourceByte;

        /* Bulk data transfer */
        while(WordCount--)
        {
            /* Transfer a full word */
            *(--DestinationWord) = *(--SourceWord);
        }

        /* Downgrade the pointers back to byte */
        DestinationByte = (PCHAR)DestinationWord;
        SourceByte = (PCHAR)SourceWord;

        /* Sequentially transfer any remaining bytes */
        while(Remainder--)
        {
            /* Transfer a single byte */
            *(--DestinationByte) = *(--SourceByte);
        }
    }
    else
    {
        /* Calculate the number of leading bytes */
        BytesToAlign = (sizeof(ULONG_PTR) - (DestinationPointer & (sizeof(ULONG_PTR) - 1))) & (sizeof(ULONG_PTR) - 1);
        if(BytesToAlign > Length)
        {
            /* Clamp the alignment requirement */
            BytesToAlign = Length;
        }

        /* Compute the alignment byte count from the remaining payload */
        Length -= BytesToAlign;

        /* Initialize the pointers for a forward traversal */
        DestinationByte = (PCHAR)DestinationPointer;
        SourceByte = (PCHAR)SourcePointer;

        /* Sequentially copy the unaligned leading bytes */
        while(BytesToAlign--)
        {
            /* Transfer a single byte */
            *DestinationByte++ = *SourceByte++;
        }

        /* Compute the number of full words and any leftover */
        WordCount = Length / sizeof(ULONG_PTR);
        Remainder = Length & (sizeof(ULONG_PTR) - 1);

        /* Elevate the byte pointers to word pointers */
        DestinationWord = (PULONG_PTR)DestinationByte;
        SourceWord = (PULONG_PTR)SourceByte;

        /* Bulk data transfer */
        while(WordCount--)
        {
            /* Transfer a full word */
            *DestinationWord++ = *SourceWord++;
        }

        /* Downgrade the pointers back to byte */
        DestinationByte = (PCHAR)DestinationWord;
        SourceByte = (PCHAR)SourceWord;

        /* Sequentially transfer any remaining bytes */
        while(Remainder--)
        {
            /* Transfer a single byte */
            *DestinationByte++ = *SourceByte++;
        }
    }
}

/**
 * This routine copies a block of memory either forward of backward, depeding
 * if source and destination buffers overlap or not.
 *
 * @param Destination
 *        Supplies a pointer to the buffer where data will be copied to.
 *
 * @param Source
 *        Supplies a pointer to the source buffer that will be copied.
 *
 * @param Length
 *        Specifies the number of bytes to copy.
 *
 * @return This routine does not return any value.
 *
 * @since NT 3.5
 */
XTAPI
VOID
RTL::Memory::MoveMemory(OUT PVOID Destination,
                        IN PCVOID Source,
                        IN SIZE_T Length)
{
    /* Copy the memory */
    CopyMemory(Destination, Source, Length);
}

/**
 * This routine compares the first bytes of the specified memory buffers.
 *
 * @param LeftBuffer
 *        Supplies a pointer to the first block of memory to compare.
 *
 * @param RightBuffer
 *        Supplies a pointer to the second block of memory to compare.
 *
 * @param Length
 *        Specifies a number of bytes to compare.
 *
 * @return Returns TRUE if both buffers are equal up to the specified length, or FALSE otherwise.
 *
 * @since XT 1.0
 */
XTAPI
BOOLEAN
RTL::Memory::SameMemory(IN PCVOID LeftBuffer,
                        IN PCVOID RightBuffer,
                        IN SIZE_T Length)
{
    return (CompareMemory(LeftBuffer, RightBuffer, Length) == Length) ? TRUE : FALSE;
}

/**
 * This routine fills a section of memory with a specified byte.
 *
 * @param Destination
 *        Supplies a pointer to the buffer to fill.
 *
 * @param Byte
 *        Supplies a pattern to fill memory.
 *
 * @param Length
 *        Specifies a number of bytes to store in memory.
 *
 * @return This routine does not return any value.
 *
 * @since XT 1.0
 */
XTAPI
VOID
RTL::Memory::SetMemory(OUT PVOID Destination,
                       IN UCHAR Byte,
                       IN SIZE_T Length)
{
    PCHAR DestinationBytes = (PCHAR)Destination;

    /* Fill the buffer with specified byte */
    while(Length--)
    {
        *DestinationBytes++ = Byte;
    }
}

/**
 * This routine fills a section of memory with zeroes.
 *
 * @param Destination
 *        Supplies a pointer to the buffer to fill.
 *
 * @param Length
 *        Specifies a number of bytes to be filled with zeroes.
 *
 * @return This routine does not return any value.
 *
 * @since NT 3.5
 */
XTAPI
VOID
RTL::Memory::ZeroMemory(OUT PVOID Destination,
                        IN SIZE_T Length)
{
    /* Fill the buffer with zeroes */
    SetMemory(Destination, 0, Length);
}