/*---------------------------------------------------------------------------*
  Project:     Compress/uncompress library
  File:        CXUncompression.h
  Programmer:  Makoto Takano

  Copyright 2005 Nintendo. All rights reserved.

  These coded instructions, statements, and computer programs contain
  proprietary information of Nintendo of America Inc. and/or Nintendo
  Company Ltd., and are protected by Federal copyright law. They may
  not be disclosed to third parties or copied or duplicated in any form,
  in whole or in part, without the prior written consent of Nintendo.
 *---------------------------------------------------------------------------*/

#include <dolphin/types.h>
#include <dolphin/os.h>
#include <revolution/cx/CXUncompression.h>
#include "CXUtil.h"


//======================================================================
//          Expanding compressed data
//======================================================================

/*---------------------------------------------------------------------------*
  Name:         CXGetUncompressedSize

  Description:  Gets the data size after decompression.
                This function can be used for data in all compression formats handled by CX.

  Arguments:    srcp :  Starting address of the compressed data

  Returns:      Data size after decompression
 *---------------------------------------------------------------------------*/
u32 CXGetUncompressedSize( const void *srcp )
{
    u32 size = CXiConvertEndian_( *(u32*)srcp ) >> 8;
    if ( size == 0 )
    {
        size = CXiConvertEndian_( *((u32*)srcp + 1) );
    }
    return size;
}


/*---------------------------------------------------------------------------*
  Name:         CXUncompressAny

  Description:  Determines the compression type from the data header and executes the proper decompression process.
                
                Decompression processes for all compression types are linked so it might be better to execute functions for each compression type if not using compression formats other than specified format.
                
                

  Arguments:    srcp    Source address
                destp   Destination address

  Returns:      None.
 *---------------------------------------------------------------------------*/
void CXUncompressAny( const void* srcp, void* destp )
{
    switch ( CXGetCompressionType( srcp ) )
    {
    // Run-length compressed data
    case CX_COMPRESSION_RL:
        CXUncompressRL( srcp, destp );
        break;
    // LZ77-compressed data
    case CX_COMPRESSION_LZ:
        CXUncompressLZ( srcp, destp );
        break;
    // Huffman-compressed data
    case CX_COMPRESSION_HUFFMAN:
        CXUncompressHuffman( srcp, destp );
        break;
    // Difference filter
    case CX_COMPRESSION_DIFF:
        CXUnfilterDiff( srcp, destp );
        break;
    default:
        ASSERTMSG( 0, "Unknown compressed format" );
    }
}


/*---------------------------------------------------------------------------*
  Name:         CXUncompressRL

  Description:  8-bit decompression of run-length compressed data

  - Decompresses run-length compressed data, writing in 8 bit units.
  - Use 4 byte alignment for the source address.

  - Data header
      u32 :4                  Reserved
          compType:4          Compression type( = 3)
          destSize:24         Data size after decompression
  
  - Flag data format
      u8  length:7            Decompressed data length - 1 (When not compressed)
                              Decompressed data length - 3 (only compress when the contiguous length is 3 bytes or greater)
          flag:1              (0, 1) = (not compressed, compressed)
  
  Arguments:    *srcp   Source address
                *destp   Destination address

  Returns:      None.
 *---------------------------------------------------------------------------*/
void CXUncompressRL( const void *srcp, void *destp )
{
    const u8 *pSrc  = srcp;
    u8       *pDst  = destp;
    u32      destCount = CXiConvertEndian_( *(u32*)pSrc ) >> 8;
    pSrc += 4;
    
    if ( destCount == 0 )
    {
        destCount = CXiConvertEndian_( *(u32*)pSrc );
        pSrc += 4;
    }
    
    while ( destCount > 0 )
    {
        u8  flags  = *pSrc++;
        u32 length = flags & 0x7fU;
        if ( !(flags & 0x80) )
        {   
            length++;
            if ( length > destCount )
            // Measures for buffer overrun when invalid data is decompressed.
            {
                length = destCount;
            }
            
            destCount -= length;
            do
            {
                *pDst++ = *pSrc++;
            } while ( --length > 0 );
        }
        else
        {
            u8 srcTmp;
            
            length    += 3;
            if ( length > destCount )
            // Measures for buffer overrun when invalid data is decompressed.
            {
                length = destCount;
            }
            
            destCount -= length;
            srcTmp    = *pSrc++;
            do
            {
                *pDst++ =  srcTmp;
            } while ( --length > 0 );
        }
    }
}


/*---------------------------------------------------------------------------*
  Name:         CXUncompressLZ
  
  Description:  8-bit decompression of LZ77 compressed data
  
  * Expands LZ77-compressed data and writes it in 8-bit units.
  - Use 4 byte alignment for the source address.
  
  - Data header
      u32 :4                  Reserved
          compType:4          Compression type( = 1)
          destSize:24         Data size after decompression
  
  - Flag data format
      u8  flags               Compression/no compression flag
                              (0, 1) = (not compressed, compressed)
  - Code data format (Big Endian)
      u16 length:4            Decompressed data length - 3 (only compress when the match length is 3 bytes or greater)
          offset:12           Match data offset - 1
  
  Arguments:    *srcp   Source address
                *destp   Destination address
  
  Returns:      None.
 *---------------------------------------------------------------------------*/
void CXUncompressLZ( const void *srcp, void *destp )
{
    const u8* pSrc      = srcp;
    u8*       pDst      = destp;
    u32       destCount = CXiConvertEndian_( *(u32 *)pSrc ) >> 8;
    BOOL      exFormat  = (*pSrc & 0x0F)? TRUE : FALSE;
    
    pSrc += 4;
    
    if ( destCount == 0 )
    {
        destCount = CXiConvertEndian_( *(u32*)pSrc );
        pSrc += 4;
    }
    
    while ( destCount > 0 )
    {
        u32 i;
        u32 flags = *pSrc++;
        for ( i = 0; i < 8; ++i )
        {
            if ( !(flags & 0x80) )
            {
                *pDst++ = *pSrc++;
                destCount--;
            }
            else
            {
                s32 length = (*pSrc >> 4);
                s32 offset;
                
                if ( ! exFormat )
                {
                    length += 3;
                }
                else
                {
                    // LZ77 extended format
                    if ( length == 1 )
                    {
                        length =  (*pSrc++ & 0x0F) << 12;
                        length |= (*pSrc++) << 4;
                        length |= (*pSrc >> 4);
                        length += 0xFF + 0xF + 3;
                    }
                    else if ( length == 0 )
                    {
                        length =  (*pSrc++ & 0x0F) << 4;
                        length |= (*pSrc >> 4);
                        length += 0xF + 2;
                    }
                    else
                    {
                        length += 1;
                    }
                }
                offset = (*pSrc++ & 0x0f) << 8;
                offset = (offset | *pSrc++) + 1;
                if ( length > destCount )
                // Measures for buffer overrun when invalid data is decompressed.
                {
                    length = (s32)destCount;
                }
                destCount -= length;
                do
                {
                    *pDst++ = pDst[ -offset ];
                } while ( --length > 0 );
            }
            if ( destCount <= 0 )
            {
                break;
            }
            flags <<= 1;
        }
    }
}


/*---------------------------------------------------------------------------*
  Name:         CXUncompressHuffman
  
  Description:  Decompression of Huffman compressed data
  
  - Decompresses Huffman compressed data, writing in 32 bit units.
  - Use 4 byte alignment for the source address.
  - Use 4-byte alignment for the destination address.
  - The target decompression buffer size must be prepared in 4-byte multiples.
  
  - Data header
      u32 bitSize:4           1 data bit size (Normally 4|8)
          compType:4          Compression type( = 2)
          destSize:24         Data size after decompression
  
  - Tree table
      u8           treeSize        Tree table size/2 - 1
      TreeNodeData nodeRoot        Root node
  
      TreeNodeData nodeLeft        Root left node
      TreeNodeData nodeRight       Root right node
  
      TreeNodeData nodeLeftLeft    Left left node
      TreeNodeData nodeLeftRight   Left right node
  
      TreeNodeData nodeRightLeft   Right left node
      TreeNodeData nodeRightRight  Right right node
  
              �E
              �E
  
    The compressed data itself follows
  
  - TreeNodeData structure
      u8  nodeNextOffset:6 :   Offset to the next node data - 1 (2 byte units)
          rightEndFlag:1      Right node end flag
          leftEndzflag:1      Left node end flag
                              When the end flag is set
                              There is data in next node
  
  Arguments:    *srcp   Source address
                *destp   Destination address

  Returns:      None.
 *---------------------------------------------------------------------------*/
void CXUncompressHuffman( const void *srcp, void *destp )
{
#define TREE_END 0x80
    const u32 *pSrc          = srcp;
    u32       *pDst          = destp;
    s32       destCount      = (s32)( CXiConvertEndian_( *pSrc ) >> 8 );
    u8        *treep         = (destCount != 0)? ((u8*)pSrc + 4) : ((u8*)pSrc + 8);
    u8        *treeStartp    = treep + 1;
    u32       dataBit        = *(u8*)pSrc & 0x0FU;
    u32       destTmp        = 0;
    u32       destTmpCount   = 0;
    u32       destTmpDataNum = 4 + ( dataBit & 0x7 );
    
    if ( destCount == 0 )
    {
        destCount = (s32)( CXiConvertEndian_( *(pSrc + 1) ) );
    }
    
    pSrc  = (u32*)( treep + ((*treep + 1) << 1) );
    treep = treeStartp;
    
    while ( destCount > 0 )
    {
        s32 srcCount = 32;
        u32 srcTmp   = CXiConvertEndian_( *pSrc++ );      // Endian strategy
        while ( --srcCount >= 0 )
        {
            u32 treeShift = (srcTmp >> 31) & 0x1;
            u32 treeCheck = *treep;
            treeCheck <<= treeShift;
            treep = (u8*)( (((u32)treep >> 1) << 1) + (((*treep & 0x3f) + 1) << 1) + treeShift );
            if ( treeCheck & TREE_END )
            {
                destTmp >>= dataBit;
                destTmp |= *treep << (32 - dataBit);
                treep = treeStartp;
                if ( ++destTmpCount == destTmpDataNum )
                {
                    // Over-access until the last 4-byte alignment of the decompression buffer
                    *pDst++ = CXiConvertEndian_(destTmp); // Endian strategy
                    destCount -= 4;
                    destTmpCount = 0;
                }
            }
            if ( destCount <= 0 )
            {
                break;
            }
            srcTmp <<= 1;
        }
    }
}


/*---------------------------------------------------------------------------*
  Name:         CXiHuffImportTree

  Description:  Expands the Huffman table.

  Arguments:    pTable  
                srcp    
                bitSize 

  Returns:      
 *---------------------------------------------------------------------------*/
static u32
CXiHuffImportTree( u16* pTable, const u8* srcp, u8 bitSize )
{
    u32 tableSize;
    u32 idx     = 1;
    u32 data    = 0;
    u32 bitNum  = 0;
    u32 bitMask = (1 << bitSize) - 1U;
    u32 srcCnt  = 0;
    const u32 MAX_IDX = (u32)( (1 << bitSize) * 2 );
    
    if ( bitSize > 8 )
    {
        tableSize = CXiConvertEndian16_( *(u16*)srcp );
        srcp   += 2;
        srcCnt += 2;
    }
    else
    {
        tableSize = *srcp;
        srcp   += 1;
        srcCnt += 1;
    }
    tableSize = (tableSize + 1) * 4;
    
    while ( srcCnt < tableSize )
    {
        while ( bitNum < bitSize )
        {
            data <<= 8;
            data |= *srcp++;
            ++srcCnt;
            bitNum += 8;
        }
        
        if ( idx < MAX_IDX )
        {
            pTable[ idx++ ] = (u16)( ( data >> (bitNum - bitSize) ) & bitMask );
        }
        bitNum -= bitSize;
    }
    return tableSize;
}

typedef struct
{
   const u8* srcp;
   u32       cnt;
   u32       stream;
   u32       stream_len;
}
BitReader;

static inline void
BitReader_Init( BitReader* context, const u8* srcp )
{
    context->srcp       = srcp;
    context->cnt        = 0; 
    context->stream     = 0;
    context->stream_len = 0;
}

static u8
BitReader_Read( BitReader* context )
{
    u8 bit;
    if ( context->stream_len == 0 )
    {
        context->stream     = context->srcp[context->cnt++];
        context->stream_len = 8;
    }
    bit = (u8)( (context->stream >> (context->stream_len - 1)) & 0x1 );
    context->stream_len--;
    return bit;
}


#define ENC_OFFSET_WIDTH

/*---------------------------------------------------------------------------*
  Name:         CXUncompressLH

  Description:  Decompress LZ-Huffman (combined) compression.
  
  Arguments:    *srcp   Source address
                *destp   Destination address
                *work   Work buffer
                        The required size is CX_UNCOMPRESS_LH_WORK_SIZE (2176B)

  Returns:      None.
 *---------------------------------------------------------------------------*/
void
CXUncompressLH( const u8* srcp, u8* dstp, void* work )
{
#define LENGTH_BITS  9
#if defined(ENC_OFFSET_WIDTH)
    #define OFFSET_BITS  5
    #define OFFSET_MASK  0x07
    #define LEAF_FLAG    0x10
    u16 offset_bit;
#else
    #define OFFSET_BITS  12
    #define OFFSET_MASK  0x3FF
    #define LEAF_FLAG    0x800
#endif
    u32       dstSize;
    u32       dstCnt = 0;
    const u8  *pSrc  = srcp;
    BitReader stream;
    u16* huffTable9;
    u16* huffTable12;
    
    huffTable9  = work;
    huffTable12 = (u16*)work + (1 << LENGTH_BITS) * 2;
    
    // load the header
    dstSize = CXiConvertEndian_( *(u32*)pSrc ) >> 8;
    pSrc += 4;
    if ( dstSize == 0 )
    {
        dstSize = CXiConvertEndian_( *(u32*)pSrc );
        pSrc += 4;
    }
    
    // read the Huffman table
    pSrc += CXiHuffImportTree( huffTable9,  pSrc, LENGTH_BITS );
    pSrc += CXiHuffImportTree( huffTable12, pSrc, OFFSET_BITS );
    
    BitReader_Init( &stream, pSrc );
    
    while ( dstCnt < dstSize )
    {
        u16* nodep = huffTable9 + 1;
        u16  val;
        do 
        {
            u8  bit    = BitReader_Read( &stream );
            u32 offset = (((*nodep & 0x7F) + 1U) << 1) + bit;
            
            if ( *nodep & (0x100 >> bit) )
            {
                nodep = (u16*)((u32)nodep & ~0x3);
                val   = *(nodep + offset);
                break;
            }
            else
            {
                nodep = (u16*)((u32)nodep & ~0x3);
                nodep += offset;
            }
        } while ( 1 );
        
        if ( val < 0x100 )
        // uncompressed data
        {
            dstp[dstCnt++] = (u8)val;
        }
        else
        // compressed data
        {
            u16 length = (u16)( (val & 0xFF) + 3 );
            u16* nodep = huffTable12 + 1;
            do
            {
                u8  bit    = BitReader_Read( &stream );
                u32 offset = (((*nodep & OFFSET_MASK) + 1U) << 1) + bit;
                
                if ( *nodep & (LEAF_FLAG >> bit) )
                {
                    nodep = (u16*)((u32)nodep & ~0x3);
                    val   = *(nodep + offset);
                    break;
                }
                else
                {
                    nodep = (u16*)((u32)nodep & ~0x3);
                    nodep += offset;
                }
            } while ( 1 );
            
        #if defined(ENC_OFFSET_WIDTH)
            offset_bit = val;
            val = 0;
            if ( offset_bit > 0 )
            {
                val = 1;
                while ( --offset_bit > 0 )
                {
                    val <<= 1;
                    val |= BitReader_Read( &stream );
                }
            }
        #endif
            val += 1;
            // Measures for buffer overrun when invalid data is decompressed.
            if ( dstCnt + length > dstSize )
            {
                length = (u16)( dstSize - dstCnt );
            }
            
            while ( length-- > 0 )
            {
                dstp[dstCnt] = dstp[dstCnt - val];
                ++dstCnt;
            }
        }
    }
#undef LENGTH_BITS
#undef OFFSET_BITS
#undef OFFSET_MASK
#undef LEAF_FLAG
}


// Structure for the range coder state
typedef struct
{
    u32     low;
    u32     range;
    u32     code;       // only used during decompression
    u8      carry;      // only used during compression
    u32     carry_cnt;  // only used during compression
}
RCState;

// Range coder structure
typedef struct
{
    u32 *freq;          // Table for occurrence frequency: (1 << bitSize) * sizeof(u32) bytes
    u32 *low_cnt;       // Table for the LOW border value: (1 << bitSize) * sizeof(u32) bytes
    u32 total;          // Total: 4 bytes
    u8  bitSize;        // Bit size: 1 byte
    u8  padding_[1];    //
}
RCCompressionInfo;

#define RC_MAX_RANGE    0x80000000


/*---------------------------------------------------------------------------*
  Name:         RCInitState_

  Description:  Initializes the RC state.

  Arguments:    state: Pointer to an RC state structure

  Returns:      None.
 *---------------------------------------------------------------------------*/
static inline void
RCInitState_( RCState* state )
{
    state->low   = 0;
    state->range = RC_MAX_RANGE;
    state->code  = 0;
    state->carry = 0;
    state->carry_cnt = 0;
}

/*---------------------------------------------------------------------------*
  Name:         RCInitInfo_

  Description:  Initialize the table for the adaptive range coder.
                All occurrence frequencies are initialized to 1.

  Arguments:    info: Pointer to an RC table information structure

  Returns:      None.
 *---------------------------------------------------------------------------*/
static inline void
RCInitInfo_( RCCompressionInfo* info, u8 bitSize, void* work )
{
    u32 tableSize = (u32)(1 << bitSize);
    u32 i;
    
    info->bitSize = bitSize;
    info->freq    = (u32*)work;
    info->low_cnt = (u32*)( (u32)work + tableSize * sizeof(u32) );
    
    for ( i = 0; i < tableSize; i++ )
    {
        info->freq[ i ]    = 1;
        info->low_cnt[ i ] = i;
    }
    info->total = tableSize;
}

/*---------------------------------------------------------------------------*
  Name:         RCAAddCount_

  Description:  Updates the frequency table for an adaptive range coder.

  Arguments:    info:  Table information for a range coder
                val:  Value to add

  Returns:      None.
 *---------------------------------------------------------------------------*/
static void
RCAddCount_( RCCompressionInfo* info, u16 val )
{
    u32 i;
    u32 tableSize = (u32)(1 << info->bitSize);
    
    info->freq[ val ]++;
    info->total++;
    for ( i = (u32)(val + 1); i < tableSize; i++ )
    {
        info->low_cnt[ i ]++;
    }
    
    // Reconstruct if the total exceeds the maximum value.
    if ( info->total >= 0x00010000 )
    {
        if ( info->freq[ 0 ] > 1 )
        {
            info->freq[ 0 ] = info->freq[ 0 ] / 2;
        }
        info->low_cnt[ 0 ] = 0;
        info->total = info->freq[ 0 ];
        
        for ( i = 1; i < tableSize; i++ )
        {
            if ( info->freq[ i ] > 1 )
            {
                info->freq[ i ] >>= 1;
            }
            info->low_cnt[ i ] = info->low_cnt[ i - 1 ] + info->freq[ i - 1 ];
            info->total += info->freq[ i ];
        }
    }
}


/*---------------------------------------------------------------------------*
  Name:         RCSearch_

  Description:  Searches for the value that must be obtained next from the code, range, and low values.

  Arguments:    info:  Table information for a range coder
                code:  Current code value
                range: Current Range value
                low:   Current Low value

  Returns:      
 *---------------------------------------------------------------------------*/
static u16
RCSearch_( RCCompressionInfo* info, u32 code, u32 range, u32 low )
{
    u32 tableSize = (u32)(1 << info->bitSize);
    u32 codeVal = code - low;
    u32 i;
    u32 temp = range / info->total;
    u32 tempVal = codeVal / temp;
    
    // Binary search
    u32 left  = 0;
    u32 right = tableSize - 1;
    
    while ( left < right )
    {
        i = (left + right) / 2;
        
        if ( info->low_cnt[ i ] > tempVal )
        {
            right = i;
        }
        else
        {
            left = i + 1;
        }
    }
    
    i = left;
    while ( info->low_cnt[ i ] > tempVal )
    {
        --i;
    }
    return (u16)i;
}


/*---------------------------------------------------------------------------*
  Name:         RCGetData_

  Description:  Gets the next value from the state in RCState, then updates the state.

  Arguments:    stream  
                info    
                state   
                adaptive

  Returns:      
 *---------------------------------------------------------------------------*/
static u16
RCGetData_( const u8* srcp, RCCompressionInfo* info, RCState* state, u32* pSrcCnt )
{
#define MIN_RANGE 0x01000000
    u16 val = RCSearch_( info, state->code, state->range, state->low );
    u32 cnt = 0;
    
    {
        u32 tmp;
        tmp          =  state->range / info->total;
        state->low   += info->low_cnt[ val ] * tmp;
        state->range =  info->freq[ val ] * tmp;
    }
    
    // Update the table for occurrence frequency
    RCAddCount_( info, val );
    
    while ( state->range < MIN_RANGE )
    {
        state->code  <<= 8;
        state->code  += srcp[ cnt++ ];
        state->range <<= 8;
        state->low   <<= 8;
    }
    *pSrcCnt = cnt;
    
    return val;
#undef MIN_RANGE
}


/*---------------------------------------------------------------------------*
  Name:         CXUncompressLRC

  Description:  LZ/Range Coder combined compression

  Arguments:    *srcp   Source address
                *destp   Destination address
                *work   Work buffer
                        The required size is CX_UNCOMPRESS_LRC_WORK_SIZE (36864B)

  Returns:      None.
 *---------------------------------------------------------------------------*/
void
CXUncompressLRC( const u8* srcp, u8* dstp, void* work )
{
#define LENGTH_BITS  9
#define OFFSET_BITS  12
    RCCompressionInfo infoVal;
    RCCompressionInfo infoOfs;
    RCState           rcState;
    const u8*         pSrc = srcp;
    u32               dstCnt  = 0;
    u32               dstSize = 0;
    
    RCInitInfo_( &infoVal, LENGTH_BITS, work );
    RCInitInfo_( &infoOfs, OFFSET_BITS, (u8*)work + (1 << LENGTH_BITS) * sizeof(u32) * 2 );
    RCInitState_( &rcState );
    
    // Load the header
    dstSize = CXiConvertEndian_( *(u32*)pSrc ) >> 8;
    pSrc += 4;
    if ( dstSize == 0 )
    {
        dstSize = CXiConvertEndian_( *(u32*)pSrc );
        pSrc += 4;
    }
    
    // Load the initial code
    rcState.code = (u32)( (*pSrc       << 24) |
                          (*(pSrc + 1) << 16) |
                          (*(pSrc + 2) <<  8) |
                          (*(pSrc + 3)      ) );
    pSrc += 4;
    
    // Continue to get values from the range coder and perform LZ decompression
    while ( dstCnt < dstSize )
    {
        u32 cnt;
        u16 val = (u16)( RCGetData_( pSrc, &infoVal, &rcState, &cnt ) );
        pSrc += cnt;
        
        if ( val < 0x100 )
        // Uncompressed data
        {
            dstp[ dstCnt++ ] = (u8)val;
        }
        else
        // Compressed data
        {
            u16 length = (u16)( (val & 0xFF) + 3 );
            val = (u16)( RCGetData_( pSrc, &infoOfs, &rcState, &cnt ) + 1 );
            pSrc += cnt;
            
            // Check for a buffer overrun
            if ( dstCnt + length > dstSize )
            {
                return;
            }
            if ( dstCnt < val )
            {
                return;
            }
            
            while ( length-- > 0 )
            {
                dstp[ dstCnt ] = dstp[ dstCnt - val ];
                ++dstCnt;
            }
        }
    }
#undef LENGTH_BITS
#undef OFFSET_BITS
}



/*---------------------------------------------------------------------------*
  Name:         CXUnfilterDiff

  Description:  8-bit decompression to restore differential filter conversion.
  
    - Restores a differential filter, writing in 8 bit units.
    - Use 4 byte alignment for the source address.

  Arguments:    *srcp   Source address
                *destp   Destination address

  Returns:      None.
 *---------------------------------------------------------------------------*/
void CXUnfilterDiff( register const void *srcp, register void *destp )
{
    const u8* pSrc = srcp;
    u8*       pDst = destp;
    u32 bitSize    = *pSrc & 0xFU;
    s32 destCount  = (s32)( CXiConvertEndian_( *(u32*)pSrc ) >> 8 );
    u32 sum = 0;
    
    pSrc += 4;
    
    if ( bitSize != 1 )
    {
        // Difference calculation in units of 8 bits
        do 
        {
            u8 tmp = *(pSrc++);
            destCount--;
            sum += tmp;
            *(pDst++) = (u8)sum;
        } while ( destCount > 0 );
    }
    else
    {
        // Difference calculation in units of 16 bits
        do 
        {
            u16 tmp = CXiConvertEndian16_( *(u16*)pSrc );
            pSrc += 2;
            destCount -= 2;
            sum += tmp;
            *(u16*)pDst = CXiConvertEndian16_( (u16)sum );
            pDst += 2;
        } while ( destCount > 0 );
    }
}


/*---------------------------------------------------------------------------*
  Name:         CXGetCompressionHeader

  Description:  Gets header information from the first four bytes in the compression data.

  Arguments:    data    First 8 bytes of compressed data
 *---------------------------------------------------------------------------*/
CXCompressionHeader CXGetCompressionHeader( const void* data )
{
    CXCompressionHeader ret;
    
    ret.compType  = (u8)( (*(u8*)data & 0xF0) >> 4 );
    ret.compParam = (u8)( *(u8*)data & 0x0F );
    
    ret.destSize  = CXiConvertEndian_( *(u32*)data ) >> 8;
    if ( ret.destSize == 0 )
    {
        ret.destSize = CXiConvertEndian_( *((u32*)data + 1) );
    }
    return ret;
}