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
$96.71
Apple Inc.
-0.48
MSFT
$44.80
Microsoft Corpora
-0.07
GOOG
$598.29
Google Inc.
+2.31

MacTech Search:
Community Search:

Software Updates via MacUpdate

Microsoft Remote Desktop 8.0.8 - Connect...
With Microsoft Remote Desktop, you can connect to a remote PC and your work resources from almost anywhere. Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help... Read more
xACT 2.30 - Audio compression toolkit. (...
xACT stands for X Aaudio Compression Toolkit, an application that encodes and decodes FLAC, SHN, Monkey’s Audio, TTA, Wavpack, and Apple Lossless files. It also can encode these formats to MP3, AAC... Read more
Firefox 31.0 - Fast, safe Web browser. (...
Firefox for Mac offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals... Read more
Little Snitch 3.3.3 - Alerts you to outg...
Little Snitch gives you control over your private outgoing data. Track background activityAs soon as your computer connects to the Internet, applications often have permission to send any... Read more
Thunderbird 31.0 - Email client from Moz...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
Together 3.2 - 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. Smart storage. With simple drag-and-drop functionality,... Read more
Cyberduck 4.5 - FTP and SFTP browser. (F...
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more
iExplorer 3.4 - View and transfer all th...
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
Airmail 1.4 - Powerful, minimal email cl...
Airmail is a powerful, minimal mail client.It was designed to retain the same experience with a single or multiple accounts and provide a quick, modern and easy-to-use user experience. Airmail... Read more
Macs Fan Control 1.1.12 - Monitor and co...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more

Latest Forum Discussions

See All

Fanatic Earth Review
Fanatic Earth Review By Brittany Vincent on July 24th, 2014 Our Rating: :: BY-THE-NUMBERSUniversal App - Designed for iPhone and iPad Kemco’s stable of mobile RPGs grows, but in Fanatic Earth’s situation it’s a case of quantity... | Read more »
Together for iOS (Productivity)
Together for iOS 1.0 Device: iOS Universal Category: Productivity Price: $9.99, Version: 1.0 (iTunes) Description: Together is an app for keeping things in one place. Notes, documents, images, movies, sounds, web pages and bookmarks... | Read more »
The Phantom PI Mission Apparition (Game...
The Phantom PI Mission Apparition 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: ** Release sale! 50% off for a limited time! ** The Phantom PI Mission Apparition is a spooky, puzzly, rock’... | Read more »
The Great Prank War (Games)
The Great Prank War 1.0.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.0 (iTunes) Description: Help Mordecai, Rigby, Muscle Man and Skips take the park back from Gene and his goons with a plethora of prank-related... | Read more »
Teenage Mutant Ninja Turtles (Games)
Teenage Mutant Ninja Turtles 1.0.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.0 (iTunes) Description: Download the all new Teenage Mutant Ninja Turtles Official Movie Game! | Read more »
Dream Revenant (Games)
Dream Revenant 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: EXCLUSIVE LAUNCH PRICE ! Dream Revenant is at $1.99 for a limited time ! | Read more »
Traps n' Gemstones (Games)
Traps n' Gemstones 1.00 Device: iOS Universal Category: Games Price: $2.99, Version: 1.00 (iTunes) Description: LAUNCH SALE! 40% off, JULY ONLY! TRAPS N' GEMSTONES is an adventurous platform game, among gamers typically known as the... | Read more »
Soccer Physics (Games)
Soccer Physics 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: One-button soccer game! So dumb it's fun. "Soccer Physics is probably the funniest football game you'll play on iOS" —... | Read more »
Ex-Angry Birds Developers Release Monsu...
Ex-Angry Birds Developers Release Monsu Teaser Trailer Posted by Jennifer Allen on July 23rd, 2014 [ permalink ] Finnish developer Boomlagoon has released a teaser trailer of their forthcoming side-scrolling action platformer, | Read more »
Dragons: Rise of Berk – Tips, Tricks, an...
Things have changed in Berk, the fantasy Viking village of DreamWorks’ How to Train Your Dragon series. Dragons and Vikings, once mortal enemies, now must learn to live together in peace. Dragons: Rise of Berk lets players manage dragon-Viking... | Read more »

Price Scanner via MacPrices.net

What Should Apple’s Next MacBook Priority Be;...
Stabley Times’ Phil Moore says that after expanding its iMac lineup with a new low end model, Apple’s next Mac hardware decision will be how it wants to approach expanding its MacBook lineup as well... Read more
ArtRage For iPhone Painting App Free During C...
ArtRage for iPhone is currently being offered for free (regularly $1.99) during Comic-Con San Diego #SDCC, July 24-27, in celebration of the upcoming ArtRage 4.5 and other 64-bit versions of the... Read more
With The Apple/IBM Alliance, Is The iPad Now...
Almost since the iPad was rolled out in 2010, and especially after Apple made a 128 GB storage configuration available in 2012, there’s been debate over whether the iPad is a serious tool for... Read more
MacBook Airs on sale starting at $799, free s...
B&H Photo has the new 2014 MacBook Airs on sale for up to $100 off MSRP for a limited time. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels... Read more
Apple 27″ Thunderbolt Display (refurbished) a...
The Apple Store has Apple Certified Refurbished 27″ Thunderbolt Displays available for $799 including free shipping. That’s $200 off the cost of new models. Read more
WaterField Designs Unveils Cycling Ride Pouch...
High end computer case and bag maker WaterField Designs of San Francisco now enters the cycling market with the introduction of the Cycling Ride Pouch – an upscale toolkit with a scratch-free iPhone... Read more
Kingston Digital Ships Large Capacity Near 1T...
Kingston Digital, Inc., the Flash memory affiliate of Kingston Technology Company, Inc.,has announced its latest addition to the SSDNow V300 series, the V310. The Kingston SSDNow V310 solid-state... Read more
Apple’s Fiscal Third Quarter Results; Record...
Apple has announced financial results for its fiscal 2014 third quarter ended June 28, 2014, racking up quarterly revenue of $37.4 billion and quarterly net profit of $7.7 billion, or $1.28 per... Read more
15-inch 2.0GHz MacBook Pro Retina on sale for...
B&H Photo has the 15″ 2.0GHz Retina MacBook Pro on sale for $1829 including free shipping plus NY sales tax only. Their price is $170 off MSRP. B&H will also include free copies of Parallels... Read more
Apple restocks refurbished Mac minis for up t...
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

Jobs Board

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
Senior Interaction Designer, *Apple* Online...
**Job Summary** Apple is looking for a hands on Senior…will be a key player in designing for the Apple Online Store. The ideal designer will have a Read more
*Apple* Sales Chat Rep - Apple (United State...
…is looking for motivated, outgoing, and tech savvy individuals who want to offer Apple Customers an unparalleled customer experience over chat. At Apple , we believe Read more
Mac Expert - *Apple* Online Store Mexico -...
…MUST be fluent in English and Spanish to be considered for this position At Apple , we believe that hard work, a fun environment, creativity and innovation fuel the Read more
*Apple* Industrial Design CAD Sculptor - App...
**Job Summary** The Apple Industrial Design team is looking for a CAD sculptor/Digital 3D modeler to create high quality CAD models used in the industrial design process Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.