TweetFollow Us on Twitter

Jul 94 Challenge
Volume Number:10
Issue Number:7
Column Tag:Programmers’ Challenge

Programmers’ Challenge

By Mike Scanlin, MacTech Magazine Regular Contributing Author

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Color Space Conversion

Typically, when an RGB image is compressed into JPEG data, it is first converted into separate luminance (Y) and chrominance (U and V) components. Although JPEG doesn’t specify which color space conversion to use, a commonly used one is:

Y     0.29900000   0.58700000   0.11400000     R
U  = -0.16873590  -0.33126410   0.50000000  *  G
V     0.50000000  -0.41868760  -0.08131241     B

where R, G and B are unsigned chars (0..255). For the outputs, Y is an unsigned char (0..255) while U and V are signed chars (-128..127).

The prototype of the two functions you write are:


/* 1 */
void *RGBtoYUVInit(void);

void RGBtoYUV(rPtr, gPtr, bPtr, 
              yPtr, uPtr, vPtr,
              numPixels,privateDataPtr)
unsigned char *rPtr;
unsigned char *gPtr;
unsigned char *bPtr;
unsigned char *yPtr;
  signed char *uPtr;
  signed char *vPtr;
unsigned long numPixels;
         void *privateDataPtr;

This month you’re being given a chance to have a separate initialization routine that will not be timed (only the RGBtoYUV will count towards your time). It can create whatever lookup tables RGBtoYUV may need and return a pointer to that private data. The return value from RGBtoYUVInit will be passed to RGBtoYUV as the privateDataPtr parameter. You decide what it points to (if anything).

There are two key aspects to writing RGBtoYUV. The first is that it has to be fast (as always). The second, though, is that it has to be accurate (or else when someone reconstructs the image with the inverse conversion image quality will be lost). Even though the outputs are only 8 bits, the matrix coefficients require much more than that to represent. Your output values must equal what you would get if you carried out the matrix math with complete precision and then rounded the results down to 8 bits as the last step (with .5 rounding down to zero). For instance, if R = 3, G = 17 and B = 23 then: Y = 3*.299 + 17*.587 + 23*.114 which is 13.498. When rounded this becomes 13 which is what you should return as part of the buffer that yPtr points to.

Each of the pointers to the RGB input data and YUV output data point to a buffer filled with data of one component (so there are 6 buffers total). numPixels is between 1 and 1,000,000 and is the size of each buffer. If numPixels were 100 then rPtr would point to 100 red values and gPtr and bPtr would point to 100 corresponding green and blue values. Your routine would then set the 100 bytes pointed to by yPtr to the appropriate Y values (and likewise for the U and V values, too).

The RGB and YUV buffers will be allocated for you. Your initialization routine may allocate up to 1MB of lookup tables if it wants to (it will be able to get a contiguous 1MB piece if it needs it).

TWO MONTHS AGO WINNER

We have a new first-time winner this month. Congrats to Troy Anderson (Paradise Valley, AZ) for his somewhat large but definitely fast entry in the Flip Horizontal challenge. He was faster than second place winner Bob Boonstra (Westford, MA) in every case that I tested. No small feat considering that Bob is a three-time Challenge winner. Troy also beat another three-time winner, Bill Karsh (Chicago, IL), in almost every test case. Unfortunately, Bill may have been too ecstatic with his win last month to test every possible case this month and unfortunately I had to disqualify his entry for lack of correctness.

Here are the code sizes and times. The time numbers represents the sum of the times for many different inputs (different depths, different rowBytes, etc). Numbers in parens after a person’s name indicate how many times that person has finished in the top 5 places of all previous Programmer Challenges, not including this one:

Name time code+data

Troy Anderson 759 2442

Bob Boonstra (8) 818 1564

Allen Stenger (5) 1069 1318

Michael Panchenko 2952 616

The best way to do well at the Flip Horizontal problem is to write dedicated code to handle each possible depth. That’s exactly what Troy did. He then went even further by special casing certain common cases, such as when rowBytes is a multiple of four.

Troy also solved the flip-byte problem (that exists when the depth is less than 8) the same way that almost everyone else did: with a lookup table for each case (1-bit, 2-bit and 4-bit). For example, when you’re flipping a bitmap horizontally it becomes necessary to flip all 8 bits in a byte. With a 256 element lookup table you can do this in a single lookup.

The 8-bit, 16-bit and 32-bit deep cases are all very similar. Troy reuses similar code by letting the preprocessor fill in the types of his variables (he uses the #define T for this purpose).

Another way of doing this, if the code is similar enough for each case, is to make the whole routine a macro and have it take a parameter which represents the type (byte, short, etc) that you want the code generated for. For instance, Bob Boonstra created this macro:


/* 2 */
/* Macro DoFlipHoriz 
 handles cases where a pixel is one byte, word, or longword in size.
 */
#define DoFlipHoriz(tp) \
{ \
/* loopCount=numCols/2 has already been calculated. */ \
  if (0 < loopCount) do { \
    register tp *p,*q; \
    p = (tp *)base; \
    q = p+numCols; \
    cCount = loopCount; \
    do { \
      register tp temp; \
      temp = *p; \
      *p++ = *--q; \
      *q = temp; \
    } while (--cCount); \
    base += rowBytes; \
  } while (--rCount); \
}
and then uses it like this in part of his solution:

    register short cCount,rCount,loopCount;
    rCount = numRows;
    loopCount = numCols>>1;
    if (8 == pixSize) DoFlipHoriz(uchar) 
    else if (16==pixSize) DoFlipHoriz(ushort)
    else /*if (32==pixSize)*/ DoFlipHoriz(ulong)

You’ll get 3 copies of the macro’s code, each for a different size pixel.
Here’s Troy’s winning solution:

// MacTech Magazine Programmers' Challenge
// May, 1994
// Submitted by Troy Anderson
// 
// Copyright (c) 1994 Troy L. Anderson

#include <QDOffscreen.h>

typedef unsigned char UCHAR;

prototypes
void FlipPixMapHorz( PixMapHandle thePixMapHndl);

static void Flip_Long(  PixMapHandle theMap, 
                        short rowBytes,
                        short depth,
                        Rect* area);

static void Flip_Word(  PixMapHandle theMap, 
                        short rowBytes,
                        short depth,
                        Rect* area);

static void ExchangeWords_Long( PixMapHandle theMap, 
                                short rowBytes,
                                short depth,
                                Rect* area);

static void ExchangeWords_Word( PixMapHandle theMap, 
                                short rowBytes,
                                short depth,
                                Rect* area);

static void ExchangeWords_Byte( PixMapHandle theMap, 
                                short rowBytes,
                                short depth,
                                Rect* area);


FlipPixMapHorz
// This could be made a bit faster by in-lining the functions, but this 
is much clearer,
// and not very much slower.
void FlipPixMapHorz( PixMapHandle thePixMapHndl)
{
  short   rowBytes = (**thePixMapHndl).rowBytes & 0x7fff;
  Boolean longAligned = rowBytes % 4 == 0;
  short   depth = (**thePixMapHndl).pixelSize;
  Rect    bounds = (**thePixMapHndl).bounds;
  
  switch( depth)
  {
    case  1:
    case  2:
    case  4:
      if (longAligned)
        Flip_Long(  thePixMapHndl, 
                    rowBytes,
                    depth,
                    &bounds);
      else
        Flip_Word(  thePixMapHndl,
                    rowBytes,
                    depth,
                    &bounds);
      break;

    case  8:
      ExchangeWords_Byte( thePixMapHndl,
                          rowBytes,
                          depth,
                          &bounds);
      break;
    
    case  16:
      ExchangeWords_Word( thePixMapHndl,
                          rowBytes,
                          depth,
                          &bounds);
      break;
      
    case  32:
      ExchangeWords_Long( thePixMapHndl,
                          rowBytes,
                          depth,
                          &bounds);
      break;
  }
}


ExchangeWords_Long
long word alignment version
static void ExchangeWords_Long( PixMapHandle theMap,
                                short rowBytes,
                                short depth,
                                Rect* area)
{
#undef T
#define T long

  short       rowCells = rowBytes / sizeof(T);
  short       numCells = ((area->right - area->left) * 
                      depth + sizeof(T)*8 - 1) / 
                      (sizeof(T)*8);
  T           temp;
  register T  *cellPtr1, *cellPtr2;
  T           *aRow;
  T           *firstRow = (T*)GetPixBaseAddr( theMap);
  T           *lastRow = firstRow + rowCells * 
                        (long)(area->bottom - area->top);

    // Flip the words in each row
  for ( aRow = firstRow; aRow < lastRow; aRow += rowCells)
    for ( cellPtr1 = aRow + numCells-1, cellPtr2 = aRow;
        cellPtr1 > cellPtr2; 
        cellPtr1--, cellPtr2++)
      temp = *cellPtr1, // swap them 
      *cellPtr1 = *cellPtr2, 
      *cellPtr2 = temp;
}


ExchangeWords
word alignment version
static void ExchangeWords_Word( PixMapHandle theMap,
                                short rowBytes,
                                short depth,
                                Rect* area)
{
#undef T
#define T short

  short       rowCells = rowBytes / sizeof(T);
  short       numCells = ((area->right - area->left) * 
                      depth + sizeof(T)*8 - 1) / 
                      (sizeof(T)*8);
  T           temp;
  register T  *cellPtr1, *cellPtr2;
  T           *aRow;
  T           *firstRow = (T*)GetPixBaseAddr( theMap);
  T           *lastRow = firstRow + rowCells * 
                        (long)(area->bottom - area->top);

    // Flip the words in each row
  for ( aRow = firstRow; aRow < lastRow; aRow += rowCells)
    for ( cellPtr1 = aRow + numCells-1, cellPtr2 = aRow;
        cellPtr1 > cellPtr2; 
        cellPtr1--, cellPtr2++)
      temp = *cellPtr1, // swap them 
      *cellPtr1 = *cellPtr2, 
      *cellPtr2 = temp;
}

ExchangeWords
byte alignment version
static void ExchangeWords_Byte( PixMapHandle theMap,
                                short rowBytes,
                                short depth,
                                Rect* area)
{
#undef T
#define T char

  short       rowCells = rowBytes / sizeof(T);
  short       numCells = ((area->right - area->left) * 
                      depth + sizeof(T)*8 - 1) / 
                      (sizeof(T)*8);
  T           temp;
  register T  *cellPtr1, *cellPtr2;
  T           *aRow;
  T           *firstRow = (T*)GetPixBaseAddr( theMap);
  T           *lastRow = firstRow + rowCells * 
                        (long)(area->bottom - area->top);

    // Flip the words in each row
  for ( aRow = firstRow; aRow < lastRow; aRow += rowCells)
    for ( cellPtr1 = aRow + numCells-1, cellPtr2 = aRow;
        cellPtr1 > cellPtr2; 
        cellPtr1--, cellPtr2++)
      temp = *cellPtr1, // swap them 
      *cellPtr1 = *cellPtr2, 
      *cellPtr2 = temp;
}


Inverse tables
// Inverse tables used to flip the bits in a byte - 
// index is input, value is inverse of index

// This is the 1-bit per pixel table
static char byteFlips1[] ={ 
  0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 
  0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
  0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 
  0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
  0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 
  0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4, 
  0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 
  0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc, 
  0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 
  0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 
  0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 
  0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa, 
  0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 
  0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6, 
  0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 
  0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 
  0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 
  0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1, 
  0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 
  0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9, 
  0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 
  0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 
  0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 
  0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
  0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 
  0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
  0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 
  0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb, 
  0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 
  0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7, 
  0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 
  0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff  };
              
// This is the 2-bits per pixel table
static char byteFlips2[] ={ 
  0x00, 0x40, 0x80, 0xc0, 0x10, 0x50, 0x90, 0xd0, 
  0x20, 0x60, 0xa0, 0xe0, 0x30, 0x70, 0xb0, 0xf0,
  0x04, 0x44, 0x84, 0xc4, 0x14, 0x54, 0x94, 0xd4, 
  0x24, 0x64, 0xa4, 0xe4, 0x34, 0x74, 0xb4, 0xf4,
  0x08, 0x48, 0x88, 0xc8, 0x18, 0x58, 0x98, 0xd8, 
  0x28, 0x68, 0xa8, 0xe8, 0x38, 0x78, 0xb8, 0xf8, 
  0x0c, 0x4c, 0x8c, 0xcc, 0x1c, 0x5c, 0x9c, 0xdc, 
  0x2c, 0x6c, 0xac, 0xec, 0x3c, 0x7c, 0xbc, 0xfc, 
  0x01, 0x41, 0x81, 0xc1, 0x11, 0x51, 0x91, 0xd1, 
  0x21, 0x61, 0xa1, 0xe1, 0x31, 0x71, 0xb1, 0xf1, 
  0x05, 0x45, 0x85, 0xc5, 0x15, 0x55, 0x95, 0xd5, 
  0x25, 0x65, 0xa5, 0xe5, 0x35, 0x75, 0xb5, 0xf5, 
  0x09, 0x49, 0x89, 0xc9, 0x19, 0x59, 0x99, 0xd9, 
  0x29, 0x69, 0xa9, 0xe9, 0x39, 0x79, 0xb9, 0xf9, 
  0x0d, 0x4d, 0x8d, 0xcd, 0x1d, 0x5d, 0x9d, 0xdd, 
  0x2d, 0x6d, 0xad, 0xed, 0x3d, 0x7d, 0xbd, 0xfd, 
  0x02, 0x42, 0x82, 0xc2, 0x12, 0x52, 0x92, 0xd2, 
  0x22, 0x62, 0xa2, 0xe2, 0x32, 0x72, 0xb2, 0xf2, 
  0x06, 0x46, 0x86, 0xc6, 0x16, 0x56, 0x96, 0xd6, 
  0x26, 0x66, 0xa6, 0xe6, 0x36, 0x76, 0xb6, 0xf6, 
  0x0a, 0x4a, 0x8a, 0xca, 0x1a, 0x5a, 0x9a, 0xda, 
  0x2a, 0x6a, 0xaa, 0xea, 0x3a, 0x7a, 0xba, 0xfa, 
  0x0e, 0x4e, 0x8e, 0xce, 0x1e, 0x5e, 0x9e, 0xde, 
  0x2e, 0x6e, 0xae, 0xee, 0x3e, 0x7e, 0xbe, 0xfe, 
  0x03, 0x43, 0x83, 0xc3, 0x13, 0x53, 0x93, 0xd3, 
  0x23, 0x63, 0xa3, 0xe3, 0x33, 0x73, 0xb3, 0xf3, 
  0x07, 0x47, 0x87, 0xc7, 0x17, 0x57, 0x97, 0xd7, 
  0x27, 0x67, 0xa7, 0xe7, 0x37, 0x77, 0xb7, 0xf7, 
  0x0b, 0x4b, 0x8b, 0xcb, 0x1b, 0x5b, 0x9b, 0xdb, 
  0x2b, 0x6b, 0xab, 0xeb, 0x3b, 0x7b, 0xbb, 0xfb, 
  0x0f, 0x4f, 0x8f, 0xcf, 0x1f, 0x5f, 0x9f, 0xdf, 
  0x2f, 0x6f, 0xaf, 0xef, 0x3f, 0x7f, 0xbf, 0xff  };
            
// This is the 4-bits per pixel table
static char byteFlips4[] ={ 
  0x00, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70, 
  0x80, 0x90, 0xa0, 0xb0, 0xc0, 0xd0, 0xe0, 0xf0,
  0x01, 0x11, 0x21, 0x31, 0x41, 0x51, 0x61, 0x71, 
  0x81, 0x91, 0xa1, 0xb1, 0xc1, 0xd1, 0xe1, 0xf1, 
  0x02, 0x12, 0x22, 0x32, 0x42, 0x52, 0x62, 0x72, 
  0x82, 0x92, 0xa2, 0xb2, 0xc2, 0xd2, 0xe2, 0xf2, 
  0x03, 0x13, 0x23, 0x33, 0x43, 0x53, 0x63, 0x73, 
  0x83, 0x93, 0xa3, 0xb3, 0xc3, 0xd3, 0xe3, 0xf3, 
  0x04, 0x14, 0x24, 0x34, 0x44, 0x54, 0x64, 0x74, 
  0x84, 0x94, 0xa4, 0xb4, 0xc4, 0xd4, 0xe4, 0xf4, 
  0x05, 0x15, 0x25, 0x35, 0x45, 0x55, 0x65, 0x75, 
  0x85, 0x95, 0xa5, 0xb5, 0xc5, 0xd5, 0xe5, 0xf5, 
  0x06, 0x16, 0x26, 0x36, 0x46, 0x56, 0x66, 0x76, 
  0x86, 0x96, 0xa6, 0xb6, 0xc6, 0xd6, 0xe6, 0xf6, 
  0x07, 0x17, 0x27, 0x37, 0x47, 0x57, 0x67, 0x77, 
  0x87, 0x97, 0xa7, 0xb7, 0xc7, 0xd7, 0xe7, 0xf7, 
  0x08, 0x18, 0x28, 0x38, 0x48, 0x58, 0x68, 0x78, 
  0x88, 0x98, 0xa8, 0xb8, 0xc8, 0xd8, 0xe8, 0xf8, 
  0x09, 0x19, 0x29, 0x39, 0x49, 0x59, 0x69, 0x79, 
  0x89, 0x99, 0xa9, 0xb9, 0xc9, 0xd9, 0xe9, 0xf9, 
  0x0a, 0x1a, 0x2a, 0x3a, 0x4a, 0x5a, 0x6a, 0x7a, 
  0x8a, 0x9a, 0xaa, 0xba, 0xca, 0xda, 0xea, 0xfa, 
  0x0b, 0x1b, 0x2b, 0x3b, 0x4b, 0x5b, 0x6b, 0x7b, 
  0x8b, 0x9b, 0xab, 0xbb, 0xcb, 0xdb, 0xeb, 0xfb, 
  0x0c, 0x1c, 0x2c, 0x3c, 0x4c, 0x5c, 0x6c, 0x7c, 
  0x8c, 0x9c, 0xac, 0xbc, 0xcc, 0xdc, 0xec, 0xfc, 
  0x0d, 0x1d, 0x2d, 0x3d, 0x4d, 0x5d, 0x6d, 0x7d, 
  0x8d, 0x9d, 0xad, 0xbd, 0xcd, 0xdd, 0xed, 0xfd, 
  0x0e, 0x1e, 0x2e, 0x3e, 0x4e, 0x5e, 0x6e, 0x7e, 
  0x8e, 0x9e, 0xae, 0xbe, 0xce, 0xde, 0xee, 0xfe, 
  0x0f, 0x1f, 0x2f, 0x3f, 0x4f, 0x5f, 0x6f, 0x7f, 
  0x8f, 0x9f, 0xaf, 0xbf, 0xcf, 0xdf, 0xef, 0xff  };


Flip_Long
static void Flip_Long(  PixMapHandle theMap, 
                        short rowBytes,
                        short depth,
                        Rect* area)
{
#undef T
#define T long

  register UCHAR  temp;
  short           rowCells = rowBytes / sizeof(T);
  long            bitsPerRow = (area->right - area->left) *
                          (long)depth - 1;
  short           numCells = (bitsPerRow + sizeof(T)*8) /
                          (sizeof(T)*8);
  T*              cellPtr;
  T*              aRow;
  T*              firstRow = (T*)GetPixBaseAddr( theMap);
  T*              lastRow = firstRow + rowCells * 
                      (long)(area->bottom - area->top);
  
  register T*     cellPtr1, *cellPtr2;

  short           numBitsToShift = ((sizeof(T)*8) -
                      (bitsPerRow % (sizeof(T)*8) + 1));
  T               shiftMask;
  T*              shiftCellPtr;
  char*           flipTable;
  
  

  switch(depth)
  {
    case 1:
      flipTable = byteFlips1;
      break;
    case 2:
      flipTable = byteFlips2;
      break;
    case 4:
      flipTable = byteFlips4;
      break;
  }
            

  if (numBitsToShift)
  {
    shiftMask = (1L << numBitsToShift) - 1;

    for ( aRow = firstRow; 
        aRow < lastRow;
        aRow += rowCells)
    {
      // With each pair of cells in the row (one on the left, the other 
on the right),
      // flip the pixels in the individual cells and swap the cells with 
one another.
      for ( cellPtr1 = aRow + numCells - 1, cellPtr2 = aRow;
          cellPtr1 > cellPtr2;
          cellPtr1--, cellPtr2++)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr2)[3]];
        ((UCHAR*)cellPtr2)[3] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[1];
        ((UCHAR*)cellPtr1)[1] = 
            flipTable[((UCHAR*)cellPtr2)[2]];
        ((UCHAR*)cellPtr2)[2] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[2];
        ((UCHAR*)cellPtr1)[2] = 
            flipTable[((UCHAR*)cellPtr2)[1]];
        ((UCHAR*)cellPtr2)[1] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[3];
        ((UCHAR*)cellPtr1)[3] = 
            flipTable[((UCHAR*)cellPtr2)[0]];
        ((UCHAR*)cellPtr2)[0] = flipTable[temp];
      }
      
      // If there's an odd number of cells in the row,  there is one 
cell we haven't
      // touched.   It needs to be flipped.
      if (cellPtr1 == cellPtr2)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr1)[3]];
        ((UCHAR*)cellPtr1)[3] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[1];
        ((UCHAR*)cellPtr1)[1] = 
            flipTable[((UCHAR*)cellPtr1)[2]];
        ((UCHAR*)cellPtr1)[2] = flipTable[temp];
      }

      // Slide the pixels to the left
      for ( shiftCellPtr = aRow;
          shiftCellPtr < aRow + rowCells;
          shiftCellPtr++)
      {
        // shift the bits over
        *shiftCellPtr <<= numBitsToShift;
          
        // bring in the bits from the next cell - garbage will be brought 
in during
        // the last iteration, but it’s put into the last cell, outside 
the bounds of the 
        // image (but still in the data area)
        *shiftCellPtr |= shiftMask & 
                        (*(shiftCellPtr+1) >> 
                          (sizeof(T)*8 - numBitsToShift));
      }
    }
  }
  else  // no need to shift pixels, otherwise, just the same as previous 
loop
    for ( aRow = firstRow; aRow < lastRow; aRow += rowCells)
    {
      // With each pair of cells in the row (one on the  left, the other 
on the right),
      // flip the pixels in the individual cells and swap the cells with 
one another.
      for ( cellPtr1 = aRow + numCells - 1, cellPtr2 = aRow;
            cellPtr1 > cellPtr2;
            cellPtr1--, cellPtr2++)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] =
            flipTable[((UCHAR*)cellPtr2)[3]];
        ((UCHAR*)cellPtr2)[3] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[1];
        ((UCHAR*)cellPtr1)[1] = 
            flipTable[((UCHAR*)cellPtr2)[2]];
        ((UCHAR*)cellPtr2)[2] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[2];
        ((UCHAR*)cellPtr1)[2] = 
            flipTable[((UCHAR*)cellPtr2)[1]];
        ((UCHAR*)cellPtr2)[1] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[3];
        ((UCHAR*)cellPtr1)[3] = 
            flipTable[((UCHAR*)cellPtr2)[0]];
        ((UCHAR*)cellPtr2)[0] = flipTable[temp];
      }
      
      // If there are an odd number of cells in the row,
      // there is one cell we haven't touched.
      // It needs to be flipped.
      if (cellPtr1 == cellPtr2)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr1)[3]];
        ((UCHAR*)cellPtr1)[3] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[1];
        ((UCHAR*)cellPtr1)[1] = 
            flipTable[((UCHAR*)cellPtr1)[2]];
        ((UCHAR*)cellPtr1)[2] = flipTable[temp];
      }
    }
  }
}


Flip_Word
static void Flip_Word(  PixMapHandle theMap, 
                        short rowBytes,
                        short depth,
                        Rect* area)
{
#undef T
#define T short

  register UCHAR  temp;
  short           rowCells = rowBytes / sizeof(T);
  long            bitsPerRow = (area->right - area->left) *
                          (long)depth - 1;
  short           numCells = (bitsPerRow + sizeof(T)*8) /
                          (sizeof(T)*8);
  T*              cellPtr;
  T*              aRow;
  T*              firstRow = (T*)GetPixBaseAddr( theMap);
  T*              lastRow = firstRow + rowCells * 
                      (long)(area->bottom - area->top);
  
  register T*     cellPtr1, *cellPtr2;

  short           numBitsToShift = ((sizeof(T)*8) -
                      (bitsPerRow % (sizeof(T)*8) + 1));
  T               shiftMask;
  T*              shiftCellPtr;
  char*           flipTable;
  
  

  switch(depth)
  {
    case 1:
      flipTable = byteFlips1;
      break;
    case 2:
      flipTable = byteFlips2;
      break;
    case 4:
      flipTable = byteFlips4;
      break;
  }
            

  if (numBitsToShift)
  {
    shiftMask = (1L << numBitsToShift) - 1;

    for ( aRow = firstRow; aRow < lastRow; aRow += rowCells)
    {
      // With each pair of cells in the row (one on the left, the other 
on the right),
      // flip the pixels in the individual cells and swap the cells with 
one another.
      for ( cellPtr1 = aRow + numCells - 1, cellPtr2 = aRow;
          cellPtr1 > cellPtr2;
          cellPtr1--, cellPtr2++)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr2)[1]];
        ((UCHAR*)cellPtr2)[1] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[1];
        ((UCHAR*)cellPtr1)[1] =
            flipTable[((UCHAR*)cellPtr2)[0]];
        ((UCHAR*)cellPtr2)[0] = flipTable[temp];
      }
      
      // If there's an odd number of cells in the row, there is one cell 
we haven't
      // touched.   It needs to be flipped.
      if (cellPtr1 == cellPtr2)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr1)[1]];
        ((UCHAR*)cellPtr1)[1] = 
            flipTable[temp];
      }

      // Slide the pixels to the left
      for ( shiftCellPtr = aRow;
          shiftCellPtr < aRow + rowCells;
          shiftCellPtr++)
      {
      // shift the bits over
        *shiftCellPtr <<= numBitsToShift;
          
      // bring in the bits from the next cell - garbage will be brought 
in during last 
      // iteration, but it’s put into the last
        // cell, outside the bounds of the image (but still in the data 
area)
        *shiftCellPtr |= shiftMask & 
                        (*(shiftCellPtr+1) >> 
                          (sizeof(T)*8 - numBitsToShift));
      }
    }
  }
  else  // no need to shift pixels, otherwise,  just the same as previous 
loop
    for ( aRow = firstRow; aRow < lastRow; aRow += rowCells)
    {
      // With each pair of cells in the row (one on the 
      // left, the other on the right), flip the pixels
      // in the individual cells and swap the cells with
       // one another.
      for ( cellPtr1 = aRow + numCells - 1, cellPtr2 = aRow;
            cellPtr1 > cellPtr2;
            cellPtr1--, cellPtr2++)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr2)[1]];
        ((UCHAR*)cellPtr2)[1] = flipTable[temp];
        
        temp = ((UCHAR*)cellPtr1)[1];
        ((UCHAR*)cellPtr1)[1] = 
            flipTable[((UCHAR*)cellPtr2)[0]];
        ((UCHAR*)cellPtr2)[0] = flipTable[temp];
      }
      
      // If there are an odd number of cells in the row,
      // there is one cell we haven't touched.
      // It needs to be flipped.
      if (cellPtr1 == cellPtr2)
      {
        temp = ((UCHAR*)cellPtr1)[0];
        ((UCHAR*)cellPtr1)[0] = 
            flipTable[((UCHAR*)cellPtr1)[1]];
        ((UCHAR*)cellPtr1)[1] = flipTable[temp];
      }
    }
  }
}
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

How to manage your time in Bakery Blitz
It can be tricky, especially when you risk burning your kitchen to the ground if you forget a cake in the oven, so make sure to use these time management tricks to keep your bakery running smoothly. Don’t collect the money right away [Read more] | Read more »
Model 15 (Music)
Model 15 1.0 Device: iOS iPhone Category: Music Price: $29.99, Version: 1.0 (iTunes) Description: The Moog Model 15 App is the first Moog modular synthesizer and synthesis educational tool created exclusively for iPad, iPhone and... | Read more »
How to deal with wind in Angry Birds Act...
Angry Birds Action! is a physics-based puzzler in which you're tasked with dragging and launching birds around an obstacle-littered field to achieve a set objective. It's simple enough at first, but when wind gets introduced things can get pretty... | Read more »
How to get three stars in every level of...
Angry Birds Action! is, essentially, a pinball-style take on the pull-and-fling action of the original games. When you first boot it up, you'll likely be wondering exactly what it is you have to do to get a good score. Well, never fear as 148Apps... | Read more »
The beginner's guide to Warbits
Warbits is a turn-based strategy that's clearly inspired by Nintendo's Advance Wars series. Since turn-based strategy games can be kind of tricky to dive into, see below for a few tips to help you in the beginning. Positioning is crucial [Read... | Read more »
How to upgrade your character in Spellsp...
So you’ve mastered the basics of Spellspire. By which I mean you’ve realised it’s all about spelling things in a spire. What next? Well you’re going to need to figure out how to toughen up your character. It’s all well and good being able to spell... | Read more »
5 slither.io mash-ups we'd love to...
If there's one thing that slither.io has proved, it's that the addictive gameplay of Agar.io can be transplanted onto basically anything and it will still be good fun. It wouldn't be surprising if we saw other developers jumping on the bandwagon,... | Read more »
How to navigate the terrain in Sky Charm...
Sky Charms is a whimsical match-'em up adventure that uses creative level design to really ramp up the difficulty. [Read more] | Read more »
Victorious Knight (Games)
Victorious Knight 1.3 Device: iOS Universal Category: Games Price: $1.99, Version: 1.3 (iTunes) Description: New challenges awaits you! Experience fresh RPG experience with a unique combat mechanic, packed with high quality 3D... | Read more »
Agent Gumball - Roguelike Spy Game (Gam...
Agent Gumball - Roguelike Spy Game 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Someone’s been spying on Gumball. What the what?! Two can play at that game! GO UNDERCOVERSneak past enemy... | Read more »

Price Scanner via MacPrices.net

Global Tablet Sales Slump Continues, iPad’s F...
Another miserable showing for the global slate tablet category in calendar Q1/16, with global tablet shipments falling another 1ten percent to 46.5 million units during the according to Strategy... Read more
Revel Systems to Showcase iPad POS Platform w...
Revel Systems, specialists in iPad Point of Sale management solution for brick-and-mortar retail, food businesses and more, today announced that it will showcase its innovative iPad Point of Sale... Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Apple refurbished 2015 iMacs available for up...
Apple now has a full line of Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are... Read more
Indian Smartphone Market Grows Annually by 12...
India’s smartphone market grew by 12 percent year-over-year, with 24.4 million units shipping in Q1 2016. The top five vendors stayed the same, with Samsung in the lead, followed by Micromax, Intex... Read more
Get Notifications When Your Friend’s Phone Ba...
Calgary, Canada based Stonelight Pictures has announced the release of Battery Share 1.0.1, its new utility for iOS 9 supported devices. The company notes that people are spending more time on their... Read more
11-inch 1.6GHz/128GB MacBook Air on sale for...
Amazon has the current-generation 11″ 1.6GHz/128GB MacBook Air (sku MJVM2LL/A) on sale for $749.99 for a limited time. Their price is $150 off MSRP, and it’s the lowest price available for this model... Read more
Price drops on clearance 2015 13-inch MacBook...
B&H Photo has dropped prices on clearance 2015 13″ MacBook Airs by up to $250. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799, $200... Read more
Mac minis on sale for up to $100 off MSRP
B&H Photo has Mac minis on sale for up to $100 off MSRP including free shipping plus NY sales tax only: - 1.4GHz Mac mini: $449 $50 off MSRP - 2.6GHz Mac mini: $649 $50 off MSRP - 2.8GHz Mac mini... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $130-$200 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1169 $130 off MSRP - 13″ 2.7GHz/... Read more

Jobs Board

Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the largest premier retailer of Apple products in the nation. In order to support our growing customer base, we are currently looking for a driven Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation WHY YOU LL LIKE IT You ll be the Big Apple You ll solve problems You ll get to show your ability to handle the stress and Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.