Nine Algorithms That Changed the Future: The Ingenious Ideas That Drive Today's Computers by John MacCormick & Chris Bishop

Author:John MacCormick & Chris Bishop [MacCormick, John & Bishop, Chris]
Language: eng
Format: epub, mobi
ISBN: 9780691158198
Amazon: 0691147140
Publisher: Princeton University Press
Published: 2013-05-05T04:00:00+00:00

Numeric codes that a computer could use for storing symbols.

Meanwhile, let's get back to the shorter-symbol trick. As with many of the supposedly technical ideas described in this book, the shorter-symbol trick is something that humans do all the time without even thinking about it. The basic idea is that if you use something often enough, it's worth having a shorthand abbreviation for it. Everyone knows that “USA” is short for “United States of America”—we all save a lot of effort each time we type or say the 3-letter code “USA” instead of the full 24-letter phrase it stands for. But we don't bother with 3-letter codes for every 24-letter phrase. Do you know an abbreviation for “The sky is blue in color,” which also happens to be a 24-letter phrase? Of course not! But why? What is the difference between “United States of America” and “The sky is blue in color”? The key difference is that one of these phrases is used much more often than the other, and we can save a lot more effort by abbreviating a frequently used phrase instead of one that is rarely used.

Let's try and apply this idea to the coding system shown on the previous page. We already know that we can save the most effort by using abbreviations for things that are used frequently. Well, the letters “e' and “t” are the ones used most often in English, so let's try to use a shorter code for each of those letters. At the moment, “e” is 31 and “t” is 46—so it takes two digits to represent each of these letters. How about cutting them down to only one digit? Let's say “e” is now represented by the single digit 8, and “t” is 9. This is a great idea! Remember how we encoded the phrase “Meet your fiancé there.” earlier, using a total of 46 digits. Now we can do it as follows, using only 40 digits:

M e e t y o u r f i a n c é t h e r e .

138 8 9 005141474400323527402982009 348 448 66

Unfortunately, there is a fatal flaw in this plan. Remember that the computer does not store the spaces between the individual letters. So the encoding doesn't really look like “13 8 8 9 00 51…44 8 66.” Instead it looks like “138890051…44866.” Can you see the problem yet? Concentrate on just the first five digits, which are 13889. Notice that the code 13 represents “M,” 8 represents “e,” and 9 represents “t,” so one way of decoding the digits 13889 is to split them up as 138-8-9, giving the word “Meet.” But 88 represents the accented symbol “ú,” so the digits 13889 might also be split up as 13-88-9, which represents “Mút.” In fact the situation is even worse, because 89 represents the slightly different accented symbol “ù,” so another possible split of 13889 is 13-8-89, representing “Meù.” There is absolutely no way to tell which of the three possible interpretations is correct.

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