TweetFollow Us on Twitter

May 94 Challenge
Volume Number:10
Issue Number:5
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.

FLIP HORIZONTAL

This month’s challenge is to implement the Flip Horizontal menu item that you find in most imaging applications. Your code will flip a given pixMap from right to left. On exit from your routine the pixMap should be a horizontal mirror reflection of what it was on input.

The prototype of the function you write is:


codeexamplestart

/* 1 */

void FlipPixMapHorz(thePixMapHndl)
PixMapHandlethePixMapHndl;

codeexampleend


You flip the pixMap pixels in place. That is, you overwrite the input pixels with the output pixels as you go. Your routine needs to handle all of the possible pixMap types, including a 1-bit deep bitMap and indexed types with less than 8 bits per index. When timing solutions, equal weight will be given to each case: 1, 2, 4, 8, 16 and 32 bits per pixel.

TWO MONTHS AGO WINNER

I am happy to announce that we now have an undisputed Programmer Challenge Champion! This month marks the 3rd time this person has come in 1st place (breaking a 3-way tie). He has also finished in the top 5 places more often than any other Challenge entrant (8 times, including this one). Congrats to Bob Boonstra (Westford, MA) for his excellent solution to the Bitmap To Text challenge! His solution is about 2.6x faster than the only other entry this month, submitted by Challenge veteran Allen Stenger (Gardena, CA).

Here are the code sizes and times for two different tests. 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 Code Time 1 Time 2

Bob Boonstra (7) 1264 4 13

Allen Stenger (4) 766 11 34

Both Bob and Allen chose to use similar algorithms. They split the bitmap into character-sized cells and then tried to find a character from the given font that had a similar density. As a measure of density they both counted the number of set bits in the cell. Thus, the performance of the routine as a whole was largely dependent on how fast their bitcount code was. Bob ended up using a faster bitcount, which looks something like this:


/* 2 */
 bitCount = 0;
 if ((x = initVal) != 0) {
 do {
 bitCount++;
 x = x & (x - 1);
 } while (x != 0);
 }

where initVal is the value that you’re trying to count the set bits for. This code has the advantage that it does zero iterations of the loop if initVal is zero. Also, it only makes one iteration through the loop for each set bit.

Allen used a 256 element lookup table where each entry in the table contained a number from 0 to 8 representing the number of set bits of the index corresponding to that entry. For instance, zero-based element number 7 contained the number 3 because there are 3 set bits when you write 7 as a base 2 number, 00000111. This table lookup method is a good idea if you want to count bits in a long run of bytes but for small bit fields that are not necessarily byte aligned there is too much masking and other loop overhead.

Here’s Bob’s winning solution:

March 94 Challenge - BitMapToText
by Bob Boonstra

Strategy

The problem states that “the smallest detail in the input image [will] be roughly equal to or larger than a single character of the given font and font size.” Therefore, this solution attempts only to match the number of bits set in a given character size piece of the image with the number of bits set in the character chosen to represent that piece of the image.

The strategy is to:

(1) draw the characters from 32 to 127 in an offscreen bitmap.

(2) sort the characters in order of increasing number of bits set

(3) precalculate a mapping from pixel density to output characters

(4) loop thru the character size chunks of the image, count the number of bits set, and output the corresponding character.

Assumptions

• Width of characters is assumed to be <=32 pixels (reasonable for (6-24 point mono font)

• No assumption that actual height of font <= 24; ascent+descent+leading may exceed point size

• Ref NIM: Text pg 4-11
bitMapPtr->rowBytes * (font height) assumed < 32K


/* 3 */
#include <stdio.h>

#pragma options (honor_register, !assign_registers)

#define uchar unsigned char
#define ushort unsigned short
#define ulong unsigned long

#define EOL 0x0d
#define kErr 1
#define kFirstChar 32
#define kLastCharPlus1 128
#define kNumChars (kLastCharPlus1-kFirstChar)
#define kBytesPerBMChar sizeof(long)
#define kMaxCharWidth (8*kBytesPerBMChar)
#define kCharRowBytes 384
#define kBitsPerChunk 32
#define kMaxCharVals 512

#define DoSetMem(addr,sz,val)                            \
  { register long *p = (long *)addr;                     \
    register short count = sz;                           \
    do *p++=val; while (--count);                        \
  }

/*
Macro BitCount(x,count) increments count for each bit in x set to 1.

WARNING:  the expression (x=x--&x) in the BitCount macro is not portable, 
because the order of evaluation is undefined, but it generates correct 
fast code for (x=x&(x-1)) in THINK C.  Non-portable code is BAD FOR YOU, 
except where speed is very important, like in this Challenge.
*/

#define BitCount(x,initVal,count)  \
  if (x=initVal) do ++count; while (x = x--&x);

ushort lineHeight,charWid;
FontInfo fInfo;

short InitOffscreenBitMap(GrafPort *charPtr)
{
//
// Initialize font information
//
    Point scalePt = {1,1};
    ulong numBytes;
    GetFontInfo(&fInfo);
    lineHeight = fInfo.leading+fInfo.ascent+fInfo.descent;
    charPtr->pnLoc.v = lineHeight -fInfo.descent;
//
// Initialize GrafPort and bitmap storage 
//
    numBytes = lineHeight*kCharRowBytes;
    if (0 == (charPtr->portBits.baseAddr = 
                (QDPtr)NewPtr( numBytes )))
      return kErr;
    DoSetMem(charPtr->portBits.baseAddr,
             numBytes/sizeof(long),0);
    charPtr->portBits.rowBytes = kCharRowBytes;
    charPtr->portBits.bounds.top = 0;
    charPtr->portBits.bounds.left = 0;
    charPtr->portBits.bounds.bottom = lineHeight;
    charPtr->portBits.bounds.right = kCharRowBytes*8;
    RectRgn(charPtr->visRgn,&charPtr->portBits.bounds);
    charWid = StdTxMeas(1,"W",&scalePt,&scalePt,&fInfo);
/*if (charWid != fInfo.widMax) DebugStr("\p bad wid");*/
    if (kBytesPerBMChar*8 < charWid) return kErr;
    return 0;
  }

//
// Draw the characters of the given font into an offscreen
// bitmap.
//
void  DrawTheChars(GrafPtr charPort)
{ 
  register Point scalePt = {1,1};
  register short hPos = kMaxCharWidth-charWid;
  register short count;
  uchar chVal = kFirstChar;
  count = kNumChars; do {
    charPort->pnLoc.h = hPos;
    StdText(1,&chVal,scalePt,scalePt);
    hPos += kMaxCharWidth;
    ++chVal;
  } while (--count);
}

//
// Calculate the number of bits set in each character, for subsequent 
use in comparing
//  to a section of the bitmap.
//
void InitBitsSetArray(register char *p,register ushort *c)
{
  register short count;
  p += (ushort)fInfo.leading*kCharRowBytes;
  count = kNumChars; do {
    register ushort bitcount=0;
    register uchar *q = (uchar *)p;
    register short vCount;
    vCount = lineHeight-fInfo.leading; do {
      register ulong row;       
      BitCount(row,*(ulong *)q,bitcount);
      q += kCharRowBytes;
    } while (--vCount);
//  Following line fudges the density value for characters to account 
for the fact 
//  that the most dense character is significantly less dense than a 
dark section of a
//  bitmap.
    bitcount += bitcount>>1;
    *c++ = bitcount;
    p += kBytesPerBMChar;
  } while (--count);
}

//
// Sort the characters in order of increasing number of bits set (density).
//
void SortBitsSetArray(register ushort *v, 
                      register ushort *c)
{
  register ushort *x;
  register ushort count,val,xVal,newVal;
// Initialize sort order
  count = kNumChars; val = 0; x=c; do {
    *x++ = val;  ++val;
  } while (--count);
// Bidirectional exchange sort is good enough for this small array
  count = kNumChars-1;
  x = c;
  val = *(v+*c);
  do {
    ushort *saveC;
    ushort saveCount;
    xVal = *(c+1);
    newVal = *(v+xVal);
    if (val > /**x*/ newVal) {
//    Swap pointers
      *(c+1) = *c;   *c = xVal;
      if (count < kNumChars-1) {
        saveC=c+1;  saveCount=count;  val = *(v+*c); 
        do {
          xVal = *(c-1);  x = v+xVal;  newVal = *x;
          if (val >= newVal) break;
          *(c-1) = *c;  *c = xVal;   --c;
        } while (++count < kNumChars-1);
        count = saveCount;  c=saveC;  val = *(v+*c);
      } else {
        val = *(v+*c++);
      }
    } else {
      val = newVal;  ++c;
    }
  } while (--count);
}

//
// Initialize a mapping from number of bits set in a character-sized 
section of the
// bitmap to the character used to represent that section.
//
void InitCharPointerArray(register ushort *v, 
     register ushort *c, register ushort *p)
{
  register short count1,count2,count3;
  register short currentVal;
  count2 = kNumChars;
  count1 = -1;
  do {
    currentVal = *(v+*c);
    if (currentVal>count1) {
      count3 = (ushort)(currentVal-count1)/2;
      if (count3) do {
        *p++=*(p-1);
        if (++count1 >= kMaxCharVals) return;
      } while (--count3);
      do {
        *p++=' '+*c;
        if (++count1 >= kMaxCharVals) return;
      } while (currentVal>count1);
    }
    ++c;
  } while (--count2);
  do {
    *p++=*(p-1);
  } while (++count1<kMaxCharVals);
}

short BitMapToText(bitMapPtr,fontName,fontSize,outputFile)
BitMap *bitMapPtr;
Str255 fontName;
unsigned short fontSize;
FILE *outputFile;
{
GrafPort charPort;
GrafPtr savePort;

//
// bitsSet[x] is the number of bits set to 1 in the  representation of 
character ' '+x
// sortedCharP[y]+' ' is the y-th character in order of  increasing number 
of bits set
//
ushort bitsSet[kNumChars],sortedCharP[kNumChars];
//
// charVals[c] is the character to be output for a character size piece 
of the bitmap 
// with c bits set
//
ushort charVals[1+kMaxCharVals];

register ulong *q,*rowP;
register short count,numBitsSet;
register ulong mask;

register uchar *p;
ulong origMask;
ushort lineBytes;
short rCnt,rowBytes,hPix,fontNum,theErr;

  GetFNum(fontName,&fontNum);
  if (0 == fontNum) return (kErr);
  if (!RealFont(fontNum,fontSize)) return (kErr);
  GetPort(&savePort);
  OpenPort(&charPort);
  TextFont(fontNum);
  TextSize(fontSize);
  if (theErr = InitOffscreenBitMap(&charPort))
    return theErr;
//
// Draw characters in bitmap.  Draws them one at a time so we can align 
the characters
// within long words. 
//
  DrawTheChars(&charPort);
  SetPort(savePort);
//  
// Init charVal array of characters to output.
//
  InitBitsSetArray(charPort.portBits.baseAddr,bitsSet);
  SortBitsSetArray(bitsSet,sortedCharP);
  InitCharPointerArray(bitsSet,sortedCharP,charVals);
//
//  Process bitMap.
//
  p = (uchar *)bitMapPtr->baseAddr;
  rowBytes = bitMapPtr->rowBytes;
  lineBytes = rowBytes*lineHeight;
  rCnt = bitMapPtr->bounds.bottom - bitMapPtr->bounds.top;
  hPix = bitMapPtr->bounds.right - bitMapPtr->bounds.left;
//
// Set a mask of charWid characters using a sign-extended shift.
//
  origMask = mask = (ulong)
           ((signed long)0x80000000>>(charWid-1));
//
//  Loop on rows of characters.
//
  do {
    short numBits,bitsThisChunk,bitsToGo,hCnt;
    rowP = (ulong *)p;
    bitsThisChunk = kBitsPerChunk;
    hCnt = hPix;
    numBits = bitsToGo = charWid;
//
//  Loop on chars within current row.
//
    do {
//
//    Count bits set in current char.
//
      numBitsSet=0;
//
//    Loop on pixels in this chunk.
//
      do {
        q = rowP;
        count = lineHeight;
//
//      Count number of bits set in this chunk.
//
        do {
          register ulong ch;
          BitCount(ch,*q & mask,numBitsSet);
          q = (ulong *)((uchar *)q + rowBytes);
        } while (--count);
//
//  Continue processing current char if there are bitsToGo.
//
        if (0 == (bitsThisChunk -= numBits)) {
//        Check for end of row.
          if (hCnt < (bitsThisChunk=kBitsPerChunk))
            bitsThisChunk = hCnt;
          ++rowP;
          if (bitsToGo-=numBits) {
            if (bitsToGo > hCnt) bitsToGo = hCnt;
            mask = origMask << (charWid - bitsToGo);
            numBits = bitsToGo;
          } else {
            mask = origMask;
            break;
          }
        } else if (numBits != charWid) {
          mask = (origMask >> bitsToGo);
          break;
        } else {
          mask >>= numBits;
          break;
        }
      } while (true);  /* break if (0 == bitsToGo) */
      numBits = bitsToGo = charWid;
      if (numBits>bitsThisChunk) numBits= bitsThisChunk;
//
//  Select output character;
//
      if (numBitsSet<kMaxCharVals)
        count = *(charVals+numBitsSet);
      else count = *(charVals+kMaxCharVals);
      putc(count,outputFile);
    } while (0 < (hCnt-=charWid));
    p += lineBytes;
    putc(EOL,outputFile);
    if (0 > rCnt) break;
    if (0 > (rCnt-=lineHeight)) lineHeight += rCnt;
    mask =  origMask;
  } while (true);
  return 0;
}







  
 
AAPL
$524.94
Apple Inc.
+5.93
MSFT
$40.01
Microsoft Corpora
-0.39
GOOG
$536.10
Google Inc.
-20.44

MacTech Search:
Community Search:

Software Updates via MacUpdate

VMware Fusion 6.0.3 - Run Windows apps a...
VMware Fusion allows you to create a Virtual Machine on your Mac and run Windows (including Windows 8.1) and Windows software on your Mac. Run your favorite Windows applications alongside Mac... Read more
Tweetbot 1.5.1 - Popular iOS twitter cli...
Tweetbot is a full-featured OS X Twitter client with a lot of personality. Whether it's the meticulously-crafted interface, sounds and animation, or features like multiple timelines and column views... Read more
Mac DVDRipper Pro 4.1.7 - Copy, backup,...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
PDFpenPro 6.2 - Advanced PDF toolkit for...
PDFpenPro allows users to edit PDF's easily. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Create... Read more
PDFpen 6.2 - Edit and annotate PDFs with...
PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Features... Read more
Monolingual 1.5.9 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. It requires a 64-bit capable Intel-based Mac and at least... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
Starcraft II: Wings of Liberty 1.1.1.180...
Download the patch by launching the Starcraft II game and downloading it through the Battle.net connection within the app. Starcraft II: Wings of Liberty is a strategy game played in real-time. You... Read more
Sibelius 7.5.0 - Music notation solution...
Sibelius is the world's best-selling music notation software for Mac. It is as intuitive to use as a pen, yet so powerful that it does most things in less than the blink of an eye. The demo includes... Read more
Typinator 5.9 - Speedy and reliable text...
Typinator turbo-charges your typing productivity. Type a little. Typinator does the rest. We've all faced projects that require repetitive typing tasks. With Typinator, you can store commonly used... Read more

Latest Forum Discussions

See All

Have a Special Dead Trigger 2 Easter Bas...
Have a Special Dead Trigger 2 Easter Basket Full of Goodies, Courtesy of Madfinger Games Posted by Rob Rich on April 18th, 2014 [ permalink ] Dead Trigger 2 | Read more »
Almost All of Playdek’s Library is on Sa...
Almost All of Playdek’s Library is on Sale Right Now, and You Should Check it Out Posted by Rob Rich on April 18th, 2014 [ permalink ] Playdek has released quite a few great iOS ports of board and card games over the years, and now most of them... | Read more »
Zynga Launches Brand New Farmville Exper...
Zynga Launches Brand New Farmville Experience with Farmville 2: Country Escape Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
David. Review
David. Review By Cata Modorcea on April 18th, 2014 Our Rating: :: MINIMALISTIC IN A DIFFERENT WAYUniversal App - Designed for iPhone and iPad David is a minimalistic game wrapped inside of a soothing atmosphere in which the hero... | Read more »
Eyefi Unveils New Eyefi Cloud Service Th...
Eyefi Unveils New Eyefi Cloud Service That Allows Users to Share Media Across Personal Devices Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
Tales from the Dragon Mountain: The Lair...
Tales from the Dragon Mountain: The Lair Review By Jennifer Allen on April 18th, 2014 Our Rating: :: STEADY ADVENTURINGiPad Only App - Designed for the iPad Treading a safe path, Tales from the Dragon Mountain: The Lair is a... | Read more »
Yahoo Updates Flickr App with Advanced E...
Yahoo Updates Flickr App with Advanced Editing Features and More Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
My Incredible Body - A Kid's App to...
My Incredible Body - A Kid's App to Learn about the Human Body 1.1.00 Device: iOS Universal Category: Education Price: $2.99, Version: 1.1.00 (iTunes) Description: Wouldn’t it be cool to look inside yourself and see what was going on... | Read more »
Trials Frontier Review
Trials Frontier Review By Carter Dotson on April 18th, 2014 Our Rating: :: A ROUGH LANDINGUniversal App - Designed for iPhone and iPad Trials Frontier finally brings the famed stunt racing franchise to mobile, but how much does its... | Read more »
Evernote Business Notebook by Moleskin I...
Evernote Business Notebook by Moleskin Introduced – Support Available in Evernote for iOS Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »

Price Scanner via MacPrices.net

Deal Alert! 13-inch MacBook Pro on sale for $...
Best Buy has the 13″ 2.5GHz MacBook Pro on sale for $999.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $200 off MSRP. Price is valid... Read more
Free HopTo 2.2 Helps Enhance Your Productivit...
The HopTo app helps you do more on your iPad by providing more and easier adaccess to files and documents. Version 2.2 adds Egnyte and HopTo’s Mac OSX File Connector. If you already have the hopTo... Read more
National Distracted Driving Awareness Month:...
As the country recognizes National Distracted Driving Awareness Month, Sprint is reminding wireless consumers to focus on driving while behind the wheel, to not text or email while driving, and to... Read more
13-inch 2.4GHz Retina MacBook Pro available f...
Abt has the 13″ 2.4GHz 128GB Retina MacBook Pro available for $1229 including free shipping. Their price is $70 off MSRP. Read more
iMacs on sale for up to $160 off MSRP this we...
Best Buy has iMacs on sale for up to $160 off MSRP for a limited time. Choose free home shipping or free instant local store pickup (if available). Prices are valid for online orders only, in-store... Read more
iPad Airs on sale this weekend for up to $100...
Best Buy has WiFi iPad Airs on sale for $50 off MSRP and WiFi + Cellular iPad Airs on sale for $100 off MSRP on their online store for a limited time, with prices now starting at $449. Choose free... Read more
Apple restocks refurbished Mac minis starting...
The Apple Store has restocked Apple Certified Refurbished Mac minis for up to $150 off the cost of new models. Apple’s one-year warranty is included with each mini, and shipping is free: - 2.5GHz Mac... Read more
Hyundai Brings Apple CarPlay To The 2015 Sona...
Hyundai Motor America has announced it will bring Apple CarPlay functionality to the 2015 Sonata. CarPlay is pitched as a smarter, safer and easier way to use iPhone in the car and gives iPhone users... Read more
Updated iPads Coming Sooner Than We Had Thoug...
MacRumors, cites KGI securities analyst Ming Chi Kuo, well-respected as an Apple product prognisticator, saying that Apple will introduce an upgraded iPad Air and iPad mini in 2014/Q3, meaning the... Read more
Toshiba Unveils New High And Low End Laptop M...
Toshiba has announced new laptop models covering both the high-end and low-end of the notebook computer spectrum. Toshiba 4K Ultra HD Laptop Toshiba’s new Satellite P55t features one of the world’s... Read more

Jobs Board

Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Inc. Research Data Specialist - Appl...
…of Worldwide Market Research & Intelligence. The team is responsible for conducting Apple branded consumer market research. It is also responsible for analyzing data Read more
*Apple* Automotive Parts Department position...
Apple Automotive is one of the fastest growing dealer…and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.