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
$96.13
Apple Inc.
+0.53
MSFT
$42.86
Microsoft Corpora
-0.30
GOOG
$566.07
Google Inc.
-5.53

MacTech Search:
Community Search:

Software Updates via MacUpdate

Data Rescue 3.2.4 - Recover lost data on...
Data Rescue is a robust and reliable hard-drive recovery solution for your Mac. Recover lost or deleted files, mount corrupted drives, and more -- Data Rescue offers complete relief from crippling... Read more
Adobe Lightroom 5.6 - Import, develop, a...
Adobe Lightroom software helps you bring out the best in your photographs, whether you're perfecting one image, searching for ten, processing hundreds, or organizing thousands. Create incredible... Read more
OneNote 15.2 - Free digital notebook fro...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that’s too important to forget. Whether you’re at... Read more
iStat Menus 4.22 - Monitor your system r...
iStat Menus lets you monitor your system right from the menubar. Included are 8 menu extras that let you monitor every aspect of your system. Some features: CPU -- Monitor cpu usage. 7 display... Read more
Ember 1.8 - Versatile digital scrapbook....
Ember (formerly LittleSnapper) is your digital scrapbook of things that inspire you: websites, photos, apps or other things. Just drag in images that you want to keep, organize them into relevant... Read more
OmniPlan 2.3.6 - Robust project manageme...
With OmniPlan, you can create logical, manageable project plans with Gantt charts, schedules, summaries, milestones, and critical paths. Break down the tasks needed to make your project a success,... Read more
Command-C 1.1.1 - Clipboard sharing tool...
Command-C is a revolutionary app which makes easy to share your clipboard between iOS and OS X using your local WiFi network, even if the app is not currently opened. Copy anything (text, pictures,... Read more
Knock 1.1.7 - Unlock your Mac by knockin...
Knock is a faster, safer way to sign in. You keep your iPhone with you all the time. Now you can use it as a password. You never have to open the app -- just knock on your phone twice, even when it's... Read more
Mellel 3.3.6 - Powerful word processor w...
Mellel is the leading word processor for OS X and has been widely considered the industry standard since its inception. Mellel focuses on writers and scholars for technical writing and multilingual... Read more
LibreOffice 4.3.0.4 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more

Latest Forum Discussions

See All

Bio Inc. is $0.99 for the Weekend, Recei...
Bio Inc. is $0.99 for the Weekend, Receives Small Update Posted by Ellis Spice on August 1st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Happy 7th Birthday Readdle! Thank You fo...
Happy 7th Birthday Readdle! | Read more »
Sharknado: The Video Game Review
Sharknado: The Video Game Review By Lee Hamlet on August 1st, 2014 Our Rating: :: SHARKNA-DON'TUniversal App - Designed for iPhone and iPad Sharknado: The Video Game brings the craziness of the movies to iOS, though it quickly... | Read more »
Clima (Weather)
Clima 1.0 Device: iOS iPhone Category: Weather Price: $.99, Version: 1.0 (iTunes) Description: Clima show you all weather information, just beautifully simple. A series of color bars can tell you at a glance exactly current... | Read more »
Sticky Soccer Review
Sticky Soccer Review By Andrew Fisher on August 1st, 2014 Our Rating: :: STICK THIS GAMEUniversal App - Designed for iPhone and iPad Sticky Soccer puts too much emphasis on the ‘sticky’ and not enough on the ‘Soccer’ or ‘Fun’.   | Read more »
Graphics-less Apocalyptic Adventure A Da...
Graphics-less Apocalyptic Adventure A Dark Room Goes Free for a Limited Time Posted by Rob Rich on August 1st, 2014 [ permalink ] | Read more »
Fraud Tycoon Review
Fraud Tycoon Review By Rob Thomas on August 1st, 2014 Our Rating: :: UNHEALTHY CREDITUniversal App - Designed for iPhone and iPad Fraud Tycoon is a half-baked, messy, promotional tie-in that does their sponsor no favors whatsoever... | Read more »
Guardians of the Galaxy: The Universal W...
Guardians of the Galaxy: The Universal Weapon is on Sale for the Weekend Posted by Rob Rich on August 1st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Mister Beam Review
Mister Beam Review By Jordan Minor on August 1st, 2014 Our Rating: :: ILLUMINATINGUniversal App - Designed for iPhone and iPad Mister Beam’s puzzles are great. But its platforming? Not so much.   | Read more »
Hook Some More Fun With MapHook’s New Up...
Hook Some More Fun With MapHook’s New Update Posted by Jessica Fisher on August 1st, 2014 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »

Price Scanner via MacPrices.net

13-inch MacBook Airs on sale for $100 off MSR...
B&H Photo has the new 2014 13″ MacBook Airs on sale $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels Desktop and LoJack for... Read more
16GB iPad Air on sale for $399, save $100
Best Buy is offering the 16GB WiFi iPad Air for $399.99 on their online store for a limited time. Their price is $100 off MSRP. Choose free shipping or free store pickup (if available). Price is for... Read more
All Over For Tablets Or Just A Maturing, Evol...
CNN’s David Goldman weighs in on tablet sector doom and gloom, asking rhetorically: “Is this the beginning of the end for the tablet?” Answering that, he contends that hysteria and panic are... Read more
Letterspace 1.0.1 – New Free iOS Text Editor...
Bangkok, Thailand based independent developer Sittipon Simasanti has released Letterspace, a new text editor for iPhone, iPad, and iPod touch devices. Letterspace is a note taking app with an... Read more
Save up to $130 on an iPad mini with Apple re...
The Apple Store has Certified Refurbished 2nd generation iPad minis with Retina Displays available for up to $130 off the cost of new models, starting at $339. Apple’s one-year warranty is included... Read more
iPad Cannibalization Threat “Overblown”
Seeking Alpha’s Kevin Greenhalgh observes that while many commentators think Apple’s forthcoming 5.5-inch panel iPhone 6 will cannibalize iPad sales, in his estimation, these concerns are being... Read more
Primate Labs Releases July 2014 MacBook Pro P...
Primate Labs’ John Poole has posted Geekbench 3 results for most of the new MacBook Pro models that Apple released on Tuesday. Poole observes that overall performance improvements for the new MacBook... Read more
Apple Re-Releases Bugfixed MacBook Air EFI Fi...
Apple has posted a bugfixed version EFI Firmware Update 2.9 a for MacBook Air (Mid 2011) models. The update addresses an issue where systems may take longer to wake from sleep than expected, and... Read more
Save $50 on the 2.5GHz Mac mini, plus free sh...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Save up to $140 on an iPad Air with Apple ref...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more

Jobs Board

Position Opening at *Apple* - Apple (United...
**Job Summary** The Apple Store is a retail environment like no other - uniquely focused on delivering amazing customer experiences. As an Expert, you introduce people Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their 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
Sr. Product Leader, *Apple* Store Apps - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.