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;
}







  
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

NTFS 14.3.318 - $19.95
This latest version supports the new macOS 10.12 Sierra! NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and... Read more
iFFmpeg 6.2.2 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
ForeverSave 2.1.6 - Universal auto-save...
ForeverSave auto-saves all documents you're working on while simultaneously doing backup versioning in the background. Lost data can be quickly restored at any time. Define your preferred time... Read more
BetterTouchTool 1.961 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
Together 3.7 - Store and organize all of...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
EtreCheck 3.1.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Postbox 5.0.9 - Powerful and flexible em...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
DiskCatalogMaker 6.5.16 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more

Latest Forum Discussions

See All

Silent Depth Submarine Simulation (Game...
Silent Depth Submarine Simulation 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: | Read more »
Enneas Saga lets you lead your own demon...
Defend the land of Enneas Continent from the forces of evil in the new fantasy MMORPG from Lyto Mobi: Enneas Saga. Can’t wait? No problem. It’s available to download now on Android devices. | Read more »
Great zombie games in the spirit of Dead...
Dead Rising 4 arrives tomorrow, giving enthusiasts a fresh chance to take selfies with zombies and get up to other ridiculous end-of-the-world shenanigans. To really get into the spirit of things, we've gone and gathered the best zombie games that... | Read more »
Amateur Surgeon 4 Guide: Advanced tips a...
Amateur Surgeon 4 is still tackling the competition at the top of the App Store charts, so if you haven't tried it out yet, you should probably do that right away. If you've been at it for a while, though, perhaps you're ready to start expanding... | Read more »
Amateur Surgeon 4 Guide: Become the worl...
It's time to wield your trusty pizza cutter again, as Amateur Surgeon has returned with a whole fresh set of challenges (and some old, familiar ones, too). Starting anew isn't easy, especially when all you have at your disposal is a lighter, the... | Read more »
Le Parker: Sous Chef Extraordinaire (Ga...
Le Parker: Sous Chef Extraordinaire 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Telltale Games really is working on a Gu...
Telltale Games' next episodic adventure is indeed Guardians of the Galaxy. A document tied to the voice actors strike suggested that the project was in the work, but now we have direct confirmation following an announcement at the Game Awards that... | Read more »
Amateur Surgeon returns to iOS and Andro...
Amateur Surgeon and its two sequels disappeared from the App Store some time and it was sad days for all. But now, just in time for the holidays, the Adult Swim favorite makes its joyous return in the shape of Amateur Surgeon 4, a remake with... | Read more »
The best board games on mobile
Sometimes you need to ditch all of the high speed, high action games in favor of something a little more traditional. If you don't feel like parting ways from your mobile device, though, there are still plenty of ways to get that old-school fix.... | Read more »
The best Facebook Messenger Instant Game...
Facebook's new Instant Games is now here, meaning you can play games with your friends directly via Facebook. It's a fun new way to connect with friends, of course, but it's also proving to be a solid gaming experience in its own right, with a... | Read more »

Price Scanner via MacPrices.net

Slate Tablet Market Share to Fall Below 75% i...
After two years of decline, the tablet market is showing signs of new life as productivity trumps entertainment, and tablets become cost-effective computing devices for both entertainment and... Read more
Yostand Launches Indigogo campaign for iStand...
China-based startup Yostand (meaning ‘your stand’), has announced the launch of its Indigogo campaign for their newly awaited iStand7. This product is a one of a kind iPhone battery case that offers... Read more
Green App – Budget Forecasting Now Available...
Indianapolis, Indiana based CoopToons has announced the release of Green – Budget Forecasting 1.5, an update to their personal budgeting app developed exclusively for iOS devices. Green aims to be a... Read more
New 2016 13-inch 2.0GHz MacBook Pros in stock...
Overstock.com has the non-Touch Bar 13″ MacBook Pros in stock today for $150 off MSRP. Shipping is free: - 13″ 2.0GHz MacBook Pro Space Gray (MLL42LL/A): $1349.99 $150 off MSRP - 13″ 2.0GHz MacBook... Read more
15-inch 2.6GHz Silver Touch Bar MacBook Pro o...
Adorama has the new 2016 15″ 2.6GHz Silver Touch Bar MacBook Pro (MLW72LL/A) in stock and available for $2349 including free shipping. Adorama charges sales tax in NY & NJ only. Their price is $... Read more
13-inch MacBook Airs on sale for up to $180 o...
Overstock.com has 13″ MacBook Airs on sale for up to $180 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (MMGF2LL/A): $869.99 $130 off MSRP - 13″ 1.6GHz/256GB MacBook Air (sku... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros (MD101LL/A) available for $829, or $270 off original MSRP. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook... Read more
Monday roundup of Holiday Mac sales: Up to $3...
Take up to $300 off MSRP on the price of a new Apple Mac at B&H Photo today as part of their Holiday sale. Shipping is free, and B&H charges NY sales tax only. Touch Bar MacBook Pros are in... Read more
12-inch WiFi Apple iPad Pros on sale for up t...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for up to $50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP... Read more
9-inch Apple WiFi iPad Pros on sale for $20-$...
B&H Photo has 9.7″ Apple WiFi iPad Pros on sale for $20-$50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 9″ Space Gray 256GB WiFi iPad Pro: $779.95 $20 off MSRP... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 53586123 Pittsburgh, Pennsylvania, United States Posted: Nov. 28, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC Read more
*Apple* Retail - Multiple Positions- Plano,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Kansas...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Chicago...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.