Rename hint.txt and hint.text to README.md
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# Best short program
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Seonghoon Kang
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<kang.seonghoon@mearie.org>
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## Judges' comments:
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### To build:
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make kang
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### To run:
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echo "full spelling of an English cardinal numeral less than a quadrillion" | ./kang
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### Try:
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echo Nineteen hundred and eighty-four | ./kang
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echo uno | ./kang
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echo trois | ./kang
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echo fier | ./kang
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echo "shest'" | ./kang
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### Selected Judges Remarks:
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The judges were able to appreciate the Indo-European language family
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relation by making this entry successfully recognize *some* French,
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German, Italian, Russian, and Spanish numerals.
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Also worth mentioning is this entry's ability to understand the
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colloquial year numbers of the last millennium.
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We've added a linefeed to the print format for convenience.
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## Author's comments:
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## Synopsis
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This short program reads a spelt number (e.g. `forty-two`) and writes a
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corresponding decimal number (e.g. `42`). Too long for one-liners, alas,
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but it still qualifies as a *short* program as it has less than 0x100 bytes.
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It accepts a variety of spelt numbers:
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* It correctly handles `zero`.
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* Hyphen does not make a difference: `forty-two` and `forty two` are same.
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So does period or comma.
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* Cases do not make a difference either: `TWO`, `Two`, `two` are same.
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* `one` and `a` are interchangeable: `one hundred` and `a hundred` are same.
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* `and` is optional: `one hundred twenty-three` and `one hundred and twenty-three`
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are same.
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* It supports every non-negative integer less than 10<sup>15</sup>-1. It uses
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the small scale (i.e. American): `billion` is 10<sup>9</sup> and `trillion` is
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10<sup>12</sup>.
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* Sometimes, it can magically correct typos.
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It does *not* accept some spelt numbers, which I found mostly irrelevant:
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* A bare `hundred`, `thousand` etc. do not work.
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* `one million million` does not work. Get used to `one trillion`!
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## Requirements
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This program is quite portable, only requiring the following:
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* The signature `int main(int, int)` should be accepted by the linker. (Original
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version only)
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* `char` should be at least 8 bits long (as dictated by the standard), `int`
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should be at least 32 bits long, `long long` should be at least 64 bits long.
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* Both the compiler and execution environment should use an ASCII-compatible
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character set and two's complement representation.
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* Overflow and underflow on `char` should wrap around, if your `char` is unsigned.
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* [A trustworthy compiler][trustingtrust].
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[trustingtrust]: http://cm.bell-labs.com/who/ken/trust.html
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The design of the program explicitly allows for `EOF` which does not equal to -1
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(it has to be negative per the standard) and both signed and unsigned `char`,
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for example. Furthermore it is endian-independent.
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## Obfuscations (SPOILERS!)
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Many obfuscations used are typical for standard IOCCC entries:
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* Two arguments from `main` function are reused as normal variables.
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* Every conditional has been replaced with `?:` ternary operator and `||`
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short-circuiting operator.
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* It has exactly three nested `for` loops and nothing else.
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* Common two's complement tricks: `~-a` instead of `a-1`,
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`~a?...:...` instead of `a!=-1?...:...`, etc.
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* Comma operators (`,`) for multiple statements. The number of them is
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minimized, however, as it is too easy to (ab)use them.
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* It lacks most parentheses around bitwise and arithmetic operators. It was
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originally written for shortness so parentheses were **EVIL**.
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* `n["string"]` instead of `"string"[n]`. Both are fine for this program but
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I went to the former just for fun.
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* Utter lack of any kind of layouts. (Oh, except for the first column.)
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Other obfuscations are more subtle:
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* The string `"1+DIY/.K430x9G(kC["` is 18 bytes long, but actually 19 bytes
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including the final null character are used.
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* It internally represents numbers as hexadecimal. When the input is `two
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hundred and three`, it actually writes 0x203 as hexadecimal.
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* Some variables (notably, `n`) have dual uses.
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* The magic number [42][hhgg] makes an appearance.
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* It has a long long numb-`main`-er within it!
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[hhgg]: http://en.wikipedia.org/wiki/Answer_to_The_Ultimate_Question_of_Life,_the_Universe,_and_Everything
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But the most important obfuscation is the clever construction of lookup table.
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The program uses 11 different characters required for recognizing 22 lexemes:
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zero one tw- th(i)r- fo(u)r- fi- six-
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seven- eigh- nin- ten eleven twelve
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hundred(s) thousand(s) million(s) billion(s) trillion(s)
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a and -teen -ty
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So that they are internally represented as like:
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r n tw- tr- fr- f- s-
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sn- g- nn- tn ln twl
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nr(s) tsan(s) lln(s) blln(s) trlln(s)
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a an -tn -ty
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The stemmer recognizes the longest matching prefix, so every lexeme can be
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recognized by at most three characters (e.g. `trl` instead of `trlln`). This is
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also handy for ignoring plurals. But that would make that the table does not fit
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in the printable byte---11<sup>2</sup> is already almost 2<sup>7</sup>!
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The trick is to use octal; three characters (`a`, `b` and `g`) are interpreted
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as sequences of two characters (`ny`, `nn` and `nw` respectively). Asides from
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a smaller lookup table, it has many good consequences:
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* Both `a` and `and` share the common prefix, `ny`, and can be discarded
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altogether. Note that `ny` itself does not appear from other entries.
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* `thousand` is interpreted as `tsan`, which is equivalent to `tfyn` in the
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octal scheme. As it is the only entry with `tf` prefix, it can be shorten by
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one character.
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Having said this important trick, other details should be relatively easier to
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follow. The order of lookup table, for example, is very important,
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and the biggest constant 6177 is not arbitrarily chosen.
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## Acknowledgement
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The cleaner (size-optimized) version of this program was originally published
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in my website in July 2011. Sun Park and others have reviewed it and let me
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aware of possible improvements. I'd also like to thank Seo Sanghyeon for
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proof-reading remarks.
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--------------------------------------------------------------------------------
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<!--
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(c) Copyright 1984-2015, [Leo Broukhis, Simon Cooper, Landon Curt Noll][judges] - All rights reserved
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This work is licensed under a [Creative Commons Attribution-ShareAlike 3.0 Unported License][cc].
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[judges]: http://www.ioccc.org/judges.html
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[cc]: http://creativecommons.org/licenses/by-sa/3.0/
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-->
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