TweetFollow Us on Twitter

Jun 93 Challenge
Volume Number:9
Issue Number:6
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.

WHERE IN THE WORLD?

This month’s Challenge is a real world problem previously solved without reals by real MacTech reader Allen Stenger (Gardena, CA): You are given a large array of unique city names in alphabetical order ending with a sentinel of ‘ZZZ’ and a single city name to find in this array. You are to return the index of the desired city, or if it doesn’t match exactly, a list of the five closest matches. If there are more than five closest ones, return any five of them. The closeness-of-match algorithm, for purposes of this challenge, is “differing in the fewest positions from the desired name.” Take the longest of the two strings you’re comparing and each time a position doesn’t match (or is beyond the end of the shorter string) add 1 to your difference count; the smallest difference count is considered closest.

The input city list is an array of Str255s (pascal strings) in one big block where there will be, say, 200 to 1000 unique city names (in alphabetical order, all uppercase, with the ‘ZZZ’ sentinel as the last element). The city you are to find is the uppercase string pointed to by cityToFindNamePtr. The prototype of the function you write is:

Boolean FindCity(cityNames,
 cityToFindNamePtr, closestMatches)
Str255  cityNames[];
Str255  *cityToFindNamePtr;
unsigned short   closestMatches[];

If there is an exact match, return TRUE and set closestMatches[0] equal to the zero-based index of the match. If there is not an exact match, return FALSE and set closestMatches[0..4] to the five closest matches (in order of closeness, or, if they are equally close, in any order).

Allen says that this problem came up while working on the American Airlines reservation system, SABRE, a long time ago. He says that his tests then showed that city names were misspelled about 1/3rd of the time due to either poor spelling or typing by the reservation agents (no offense intended). You can use that information in your solution if you like; I will be simulating it with test data (exact matches will occur only 33% of the time I call your routine from my test bench).

TWO MONTHS AGO WINNER

Congratulations to Steve Israelson (Vancouver, B.C.) for winning the “Rotated Bits” challenge. Right on his heels is Andy Scheck (location unknown) with an entry that was half as many bytes but which was just a little too slow in some cases to win. Jeff Mallett (Hickory, NC) deserves praise for his extremely small solution which was also near the top in terms of speed. Because it is so small, it is listed here as well, after Steve’s winning solution.

There were 16 entries to this challenge. Two of them were disqualified immediately because they were in assembly (nice try) and six others were disqualified for giving incorrect results (try testing with a 9x17 bitmap). Many people e-mailed me and asked if they could assume that rowBytes was divisible by four. The answer is: no. However, you could always case out on that case early on in your routine and then call one of two rotate functions based on if (rowBytes % 4 == 0) or not. Just so long as your solution has one entry point you can do whatever you like inside.

Here’s a summary of the eight entries that gave correct results. The bytes column is the code size, test 1 is the ticks to rotate 4000 small bitmaps (20x30 and smaller) and test 2 is the ticks to rotate 400 medium size bitmaps (300x400 pixels, approx). In all cases, the bitmaps were filled with the same random data before rotating:

Name bytes test 1 test 2

Steve Israelson 740 72 638

Andy Scheck 386 75 778

Jeff Mallett 194 91 936

Patrick Breen 668 125 902

Stepan Riha 656 122 1186

Dave Darrah 362 138 1453

Jan Bruyndonckx 490 205 1785

Dominic Mazzoni 244 630 6687

Steve’s winning solution is reasonably commented so I won’t go into detail here describing how it works. I will, however, offer some peephole optimizations to make it even better.

The first thing that the optimized eye notices about his code is that he multiplies, divides and mods by 8. It’s a dangerous assumption to make that the compiler will be smart and substitute shifts and ands where it can. I always prefer to make them explicit. Thus, I would change these lines:

 srcRowX8 = srcRowBytes * 8;
 srcData = const1 + srcX / 8;
 if (remainder = (srcWidth % 8))

to these:

 srcRowX8 = srcRowBytes << 3;
 srcData = const1 + (srcX >> 3);
 if (remainder = (srcWidth & (8 - 1)))

In addition to those, there is one point in his code where he multiplies by 7. He’d be better off by multiplying by 8 (using a shift) and then subtracting one. This:

 src += srcOffset * 7;
is faster as:

 src += srcOffset << 3;
 src -= srcOffset;

After I made these changes and then ran test 2, the time went from 638 ticks to 542 ticks (it reduced the code size by 18 bytes, too).

Here’s Steve’s winning solution, followed by Jeff’s tiny solution:

/*-------------------------------------------------
 Steve Israelson
 Motion Works Corp.
-------------------------------------------------*/
void RotateBitMapClockwise(BitMap *, BitMap *);
void rotateBlock(unsigned long *,unsigned char *,
 long,unsigned char *,long);
void rotateLimitedBlock(unsigned long *,
 unsigned char *, long,unsigned char *,long,
 short);

/*-------------------------------------------------
 Rotate the bitmap from src to dst by +90 degrees.  Make 
 a table for use in the rotate block routine.  Step through 
 the src in 8x8 blocks, starting from the bottom left.  Step 
 through dst in 8x8 blocks,  starting from the top left. 
 Handle the right edge of the bitmap specially to prevent bits 
 from being rotated into memory outside of the destination.

-------------------------------------------------*/
void RotateBitMapClockwise(BitMap *src, BitMap *dst)
{
 unsigned long table[16] =
 {0x00000000, 0x00000001, 0x00000100, 0x00000101,
  0x00010000, 0x00010001, 0x00010100, 0x00010101,
  0x01000000, 0x01000001, 0x01000100, 0x01000101,
  0x01010000, 0x01010001, 0x01010100, 0x01010101};
 /* x,y co-ord of source block */
 register short  srcX, srcY;
 /* row bytes, dereferenced for speed */
 short  srcRowBytes, dstRowBytes;
 /* src rowbytes * 8, for speed */
 short  srcRowX8;
 /* width and height of src */
 short  srcWidth, srcHeight;
 /* pointer to src and dst 8x8 blocks */
 char   *srcData, *dstData;
 /* pointer to bitmaps de-referenced for speed */
 char   *srcAddr, *dstAddr;
 /* last few pixels to do specially */
 short  remainder;
 /* a constant, pre-calculated for speed */
 char   *const1;
 
 /* de-reference some constants */
 srcRowBytes = src->rowBytes;
 dstRowBytes = dst->rowBytes;
 srcAddr = src->baseAddr;
 dstAddr = dst->baseAddr;
 
 /* calculate some values */
 srcWidth = src->bounds.right - src->bounds.left;
 srcHeight = src->bounds.bottom - src->bounds.top;
 
 srcRowX8 = srcRowBytes * 8;
 const1 = srcAddr + (srcHeight - 8) * srcRowBytes;
 
 /* loop through the source doing vertical
  * slices starting at the left */
 for (srcX = 0; srcX < srcWidth - 7; srcX += 8) {
 /* bottom edge */
 srcData = const1 + srcX / 8;
 /* left edge */
 dstData = dstAddr + srcX * dstRowBytes;
 for (srcY = srcHeight - 1; srcY >= 0;
   srcY -= 8 ) {
 rotateBlock(table, (unsigned char *)srcData,
 srcRowBytes, (unsigned char *)dstData,
 dstRowBytes);
 srcData -= srcRowX8; /* next vert block */
 ++dstData; /* next horiz block */
 }
 }
 
 /* handle the last partial row by calling
  * rotateLimitedBlock() */
 if (remainder = (srcWidth % 8)) {
 /* bottom edge */
 srcData = const1 + srcX / 8; 
 /* left edge */
 dstData = dstAddr + srcX * dstRowBytes;
 for (srcY = srcHeight - 1; srcY >= 0;
   srcY -= 8 ) {
 rotateLimitedBlock(table,
 (unsigned char *)srcData, srcRowBytes, 
 (unsigned char *)dstData, dstRowBytes,
 remainder);
 srcData -= srcRowX8;
 ++dstData;
 }
 }
}

/*-------------------------------------------------
 Rotate an 8x8 block of pixels by treating the destination
 block as 2 unsigned longs (64 bits!) and using a lookup 
 table to get a mask for the value of each row in the src 
 block.  The table essentially stretches out the source byte 
 to 8 times its size and then ORs it into the destination 
 64bits.  Since the bits are in the low bit of each byte, 
 the destination has to be shifted one position to the left 
 before each OR operation. The offset values are the 
 difference to rowBytes. If we had a 64bit data type, this
 would be easier.
-------------------------------------------------*/
void rotateBlock(unsigned long *table,
 unsigned char *src, long srcOffset, 
 unsigned char *dst, long dstOffset)
{
 register unsigned long   resultLO, resultHi;
 short  x;
 
 resultLO = resultHi = 0;
 src += srcOffset * 7;
 /* compute the rotated result */
 for (x = 0; x < 8; ++x) {
 resultLO = resultLO << 1;
 resultHi = resultHi << 1;
 resultLO |= table[(*src) >> 4];
 resultHi |= table[(*src) & 0x0F];
 src -= srcOffset;
 }
 
 /* store the rotated result */
 *dst = (resultLO & 0xFF000000) >> 24;
 dst += dstOffset;
 *dst = (resultLO & 0x00FF0000) >> 16;
 dst += dstOffset;
 *dst = (resultLO & 0x0000FF00) >> 8;
 dst += dstOffset;
 *dst = resultLO & 0x000000FF;
 dst += dstOffset;
 *dst = (resultHi & 0xFF000000) >> 24;
 dst += dstOffset;
 *dst = (resultHi & 0x00FF0000) >> 16;
 dst += dstOffset;
 *dst = (resultHi & 0x0000FF00) >> 8;
 dst += dstOffset;
 *dst = resultHi & 0x000000FF;
}

/*-------------------------------------------------
 Same as other rotateBlock, except will do a
 partial block. Useful to prevent the overwriting
 of memory outside the bitmap!
-------------------------------------------------*/
void rotateLimitedBlock(unsigned long *table,
 unsigned char *src, long srcOffset, 
 unsigned char *dst, long dstOffset, short lines)
{
 register unsigned long   resultLO, resultHi;
 short  x;
 
 resultLO = resultHi = 0;
 src += srcOffset * 7;
 for (x = 0; x < 8; ++x) {
 resultLO = resultLO << 1;
 resultHi = resultHi << 1;
 resultLO |= table[(*src) >> 4];
 resultHi |= table[(*src) & 0x0F];
 src -= srcOffset;
 }
 *dst = (resultLO & 0xFF000000) >> 24;
 dst += dstOffset; if (lines == 1) return;
 *dst = (resultLO & 0x00FF0000) >> 16;
 dst += dstOffset; if (lines == 2) return;
 *dst = (resultLO & 0x0000FF00) >> 8;
 dst += dstOffset; if (lines == 3) return;
 *dst = resultLO & 0x000000FF;
 dst += dstOffset; if (lines == 4) return;
 *dst = (resultHi & 0xFF000000) >> 24;
 dst += dstOffset; if (lines == 5) return;
 *dst = (resultHi & 0x00FF0000) >> 16;
 dst += dstOffset; if (lines == 6) return;
 *dst = (resultHi & 0x0000FF00) >> 8;
 dst += dstOffset; if (lines == 7) return;
 *dst = resultHi & 0x000000FF;
}


//*********************************************************
// RotateBitMapClockwise
// By Jeff Mallett
//
// Rotates the significant bits of the srcBitMapPtr 90°
// clockwise and stores the result in dstBitMapPtr.
//*********************************************************

#define kHighShortBit0x8000
#define kBitsPerShort16

// Creates a short from bits in different rows of
// the source bitmap.  Then copies this short into
// the destination bitmap.
#define COPY_TWO_BYTES(stopValue)  \
 data = 0, bit = kHighShortBit;    \
 do {   \
 if (*srcPos & srcBit) data |= bit;\
 srcPos += srcRowShorts;  \
 } while ( (bit >>= 1) != stopValue ); \
 *(dstPos++) = data

void RotateBitMapClockwise(BitMap *srcBitMapPtr,
 BitMap *dstBitMapPtr)
{
 register unsigned short data, *srcPos, bit;
 register int j;
 register unsigned short srcBit, *dstPos, stopBit;
 register int i;
 unsigned short *baseSrcPtr;
 // shorts per row of source
 const int srcRowShorts =
   srcBitMapPtr->rowBytes >> 1;
 const int numSrcRows =
   srcBitMapPtr->bounds.bottom - srcBitMapPtr->bounds.top;
 
 dstPos = (unsigned short *)dstBitMapPtr->baseAddr;
 srcPos = baseSrcPtr =
   (unsigned short *)srcBitMapPtr->baseAddr;
 srcBit = kHighShortBit;
 
 for (i = srcBitMapPtr->bounds.right -
   srcBitMapPtr->bounds.left; i; --i) {
 // Copy one column of source to a row of destination
 for (j = numSrcRows / kBitsPerShort; j; --j) {
 COPY_TWO_BYTES(0);
 }
 if (j = numSrcRows % kBitsPerShort) {
 stopBit = kHighShortBit >> j;
 COPY_TWO_BYTES(stopBit); // Final 2 bytes
 }
 // Prepare to copy next column of source
 if ( !(srcBit >>= 1) ) {
 srcBit = kHighShortBit;
 ++baseSrcPtr;
 }
 srcPos = baseSrcPtr;
 }
}

The Rules

Here’s how it works: Each month there will be a different programming challenge presented here. First, you must write some code that solves the challenge. Second, you must optimize your code (a lot). Then, submit your solution to MacTech Magazine (formerly MacTutor). A winner will be chosen based on code correctness, speed, size and elegance (in that order of importance) as well as the postmark of the answer. In the event of multiple equally desirable solutions, one winner will be chosen at random (with honorable mention, but no prize, given to the runners up). The prize for the best solution each month is $50 and a limited edition “The Winner! MacTech Magazine Programming Challenge” T-shirt (not to be found in stores).

In order to make fair comparisons between solutions, all solutions must be in ANSI compatible C (i.e., don’t use Think’s Object extensions). Only pure C code can be used. Any entries with any assembly in them will be disqualified. However, you may call any routine in the Macintosh toolbox you want (i.e., it doesn’t matter if you use NewPtr instead of malloc). All entries will be tested with the FPU and 68020 flags turned off in THINK C. When timing routines, the latest version of THINK C will be used (with ANSI Settings plus “Honor ‘register’ first” and “Use Global Optimizer” turned on) so beware if you optimize for a different C compiler. All code should be limited to 60 characters wide. This will aid us in dealing with e-mail gateways and page layout.

The solution and winners for this month’s Programmers’ Challenge will be published in the issue two months later. All submissions must be received by the 10th day of the month printed on the front of this issue.

All solutions should be marked “Attn: Programmers’ Challenge Solution” and sent to Xplain Corporation (the publishers of MacTech Magazine) via “snail mail” or preferably, e-mail - AppleLink: MT.PROGCHAL, Internet: progchallenge@xplain.com, and CompuServe: 71552,174. If you send via snail mail, please include a disk with the solution and all related files (including contact information). See page 2 for information on “How to Contact Xplain Corporation.”

MacTech Magazine reserves the right to publish any solution entered in the Programming Challenge of the Month and all entries are the property of MacTech Magazine upon submission. The submission falls under all the same conventions of an article submission.

 
AAPL
$118.55
Apple Inc.
+0.95
MSFT
$47.84
Microsoft Corpora
+0.37
GOOG
$537.54
Google Inc.
-3.54

MacTech Search:
Community Search:

Software Updates via MacUpdate

RapidWeaver 6.0.3 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
iPhoto Library Manager 4.1.10 - Manage m...
iPhoto Library Manager lets you organize your photos into multiple iPhoto libraries. Separate your high school and college photos from your latest summer vacation pictures. Or keep some photo... Read more
iExplorer 3.5.1.9 - View and transfer al...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
MacUpdate Desktop 6.0.3 - Discover and i...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more
SteerMouse 4.2.2 - Powerful third-party...
SteerMouse is an advanced driver for USB and Bluetooth mice. It also supports Apple Mighty Mouse very well. SteerMouse can assign various functions to buttons that Apple's software does not allow,... Read more
iMazing 1.1 - Complete iOS device manage...
iMazing (was DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and from... Read more
PopChar X 7.0 - Floating window shows av...
PopChar X helps you get the most out of your font collection. With its crystal-clear interface, PopChar X provides a frustration-free way to access any font's special characters. Expanded... Read more
Carbon Copy Cloner 4.0.3 - Easy-to-use b...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
ForeverSave 2.1.3 - 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. Losing data, caused by... Read more
Voila 3.8.1 - Capture, annotate, organiz...
Voila is a screen-capture, recording, and annotation tool that is a full-featured replacement for Mac's screen-capture and screen-recording capabilities. It has a large and robust set of editing,... Read more

Latest Forum Discussions

See All

Make Way for Fat Chicken, from the Maker...
Make Way for Fat Chicken, from the Makers of Scrap Squad Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Relevant Games has announced they will be releasing their reverse tower defense game, | Read more »
Tripnary Review
Tripnary Review By Jennifer Allen on November 26th, 2014 Our Rating: :: TRAVEL BUCKET LISTiPhone App - Designed for the iPhone, compatible with the iPad Want to create a travel bucket list? Tripnary is a fun way to do exactly that... | Read more »
Ossian Studios’ RPG, The Shadow Sun, is...
Ossian Studios’ RPG, The Shadow Sun, is Now Available for $4.99 Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Mmmm, Tasty – Having the Angry Birds for...
The very first Angry Birds debuted on iOS back in 2009. When you sit back and tally up the number of Angry Birds games out there and the impact they’ve had on pop culture as a whole, you just need to ask yourself: “How would the birds taste... | Read more »
Rescue Quest Review
Rescue Quest Review By Jennifer Allen on November 26th, 2014 Our Rating: :: PATH BASED MATCH-3Universal App - Designed for iPhone and iPad Guide a wizard to safety by matching gems. Rescue Quest might not be an entirely original... | Read more »
You Can Play the Final Chapter of Lone W...
You Can Play the Final Chapter of Lone Wolf: Dawn Over V’taag Right Now Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Swords of Anima (Games)
Swords of Anima 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: A new tactical turn-based RPG experience. Command the Savior Rex Squad in an epic journey of courage and deception. Can you... | Read more »
Audio Defence: Zombie Arena
Audio Defence: Zombie Arena By Lee Hamlet on November 26th, 2014 Our Rating: :: DRAGS ITS FEETUniversal App - Designed for iPhone and iPad From the makers of Papa Sangre comes a defense game that forces players to listen carefully... | Read more »
Tales from the Borderland​s Will be Comi...
Tales from the Borderland​s Will be Coming to iOS by the End of the Year Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Telltale Games has announced | Read more »
Sunburn! Review
Sunburn! Review By Campbell Bird on November 26th, 2014 Our Rating: :: DON'T DIE ALONEUniversal App - Designed for iPhone and iPad Platform through the depths of space to make sure your entire crew dies together in this satisfying... | Read more »

Price Scanner via MacPrices.net

Early Black Friday MacBook Air sale prices, $...
 MacMall has posted early Black Friday MacBook Air sale prices. Save $101 on all models for a limited time: - 11″ 1.4GHz/128GB MacBook Air: $798 - 11″ 1.4GHz/256GB MacBook Air: $998 - 13″ 1.4GHz/... Read more
Why iPhone 6 Tablet/Laptop Cannibalization Is...
247wallst.com blogger Douglas A. McIntyre noted last week that according to research posted on the Applovin blog site the iPhone 6 is outselling the iPhone 6 Plus by a wide margin . Hardly a surprise... Read more
Worldwide Tablet Growth Expected to Slow to 7...
The global tablet market is expected to record massive deceleration in 2014 with year-over-year growth slowing to 7.2%, down from 52.5% in 2013, according to a new forecast from International Data... Read more
Touchscreen Glove Company Announces New Produ...
Surrey, United Kingdom based TouchAbility specializes in design and manufacture of a wide variety of products compatible with touchscreen devices including smartphones, tablets and computers. Their... Read more
OtterBox Alpha Glass Screen Protectors for iP...
To complement the bigger, sharper displays on the latest Apple devices, OtterBox has introduced Alpha Glass screen protectors to the iPhone 6 and iPhone 6 Plus. The fortified glass screen protectors... Read more
Early Black Friday Mac Pro sale, 6-Core 3.5GH...
 B&H Photo has the 6-Core 3.5GHz Mac Pro on sale today for $3499 including free shipping plus NY sales tax. Their price is $500 off MSRP, and it’s the lowest price available for this model from... Read more
Early Black Friday sale price: 15-inch 2.2GHz...
 B&H Photo has the 2014 15″ 2.2GHz Retina MacBook Pro on sale today for $1699.99. Shipping is free, and B&H charges NY sales tax only. Their price is $300 off MSRP, equalling Best Buy’s price... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $170 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz... Read more
Early Black Friday iPad mini 3 sale: $75 off...
 Best Buy has iPad mini 3s on sale for $75 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices available for online orders... Read more
Early Black Friday MacBook Pro sale: 15-inch...
 Best Buy has posted early Black Friday prices on 15″ Retina MacBook Pros, with models on sale for $300 off MSRP on their online store for a limited time. Choose free local store pickup (if available... Read more

Jobs Board

*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
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the 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* 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.