Rename hint.txt and hint.text to README.md
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# Most Useful
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Dave Burton <ioccc@snox.net>
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<http://snox.net/ioccc>
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## Judges' comments:
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### To use:
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make
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./prog "expression"
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or
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./prog
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(input expressions)
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### Try:
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./prog '?0x3343<<2'
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echo '?0x3343<<2' | ./prog
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./prog
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Enter:
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a=0xfeedface
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b=0xcafe
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a << 16 + b
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grep '[0-9]' prog.c
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./prog < test.in
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less calc.man
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### Selected Judges Remarks:
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"Look, Ma, no ~~hands~~ digits!"
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The place where some arithmetic operations are done, for example,
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division or modulo, are easy to find. Where are addition and subtraction?
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We were impressed with the level of detail the author "blogged" the obfuscation process.
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## Author's comments:
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calc - an integer expression calculator that outputs in both hex and decimal
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----------------------------------------------------------------------------
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All useful tools should include sufficient documentation.
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See the included man page. ;-)
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Notes
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-----
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This program is named calc. Onomatopoeia of sorts, in the visual realm.
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The formatting was easier: Form Follows Function (although [Hou][1] did this better).
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It was tempting to call it iCalc, with i for integer (and it was written on an iDevice),
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but sanity prevailed.
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Printed in 8 pt Courier, it makes aesthetically pleasing 8.5 x 11 wall art.
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[1]: http://www.ioccc.org/2011/hou/hint.html "Hou Qiming"
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prog.c vs prog.orig.c
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---------------------
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Dominik Muth observed a syntax error on `1+1`, `1-1`, `1|1`, and `1^1` when using an
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ARM based computer, although `1*1` and others worked correctly.
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This occurs because some platforms by default treat `char` as `unsigned char`.
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The original code has this weakness, which can be corrected by adding `-fsigned-char`
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to the compile line.
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The modified code is agnostic to `char` signed-ness.
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Why is this entry obfuscated/interesting?
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-----------------------------------------
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Yes, this is another calculator program.
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However, unlike any other calculator source code the author is aware of,
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this one contains no digits. At all. Anywhere. As in
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grep '[0-9]' prog.c || echo no digits!
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Nor are the digits simply obfuscated. There are no character constants.
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There is only one single, short string, and it does not contain any obfuscated digits.
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And yet the output is in decimal and hexadecimal, and it accepts octal, decimal, and hex input.
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Flow control is by `for` and `return`. It is If-less. Switch-less. While-less. Hope-less.
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Literally, if not figuratively. ;-)
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The code size is intentionally 2015, as stated by iocccsize -i,
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and can be reformatted without changes (as in rule2.c) to exactly 4096 octets.
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Finally, calc is interesting, if for no other reason than it is practically useful:
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Hex/decimal conversion, arithmetic, byte-swapping, bit-shifting, and logical operations with memory,
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on the command line, or interactively.
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But the question is why is the entry obfuscated?
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------------------------------------------------
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The code follows many industry best-practices:
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- You know what it does just by looking at it.
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- Numbers and digits have often been used for obfuscation,
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so in a bid for better clarity, this code has no digits at all.
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- In the spirit of clarity, most of the variables are declared before use, so they
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are readily visible, with single letter names that don't clutter the screen,
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in a tautological arrangement.
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- More helpful is the use of `typedef`s instead of `#define`, so the types remain useful
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even in the debugger, and source code beautifiers will not undo careful presentation.
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- `#defines` are used here in the best spirit of the preprocessor: to shorten
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repetitive constructs, not for obscurity.
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- All functions are short (and therefore easy to understand?) and do only one thing, well, ....
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- Curly braces invite endless holy wars over readability. This code only uses them
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for function definitions, thereby greatly improving readability, and reducing arguments
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about said readability.
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- One of C's many blessings (until recently) is a modicum of keywords,
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of which only 8 are used:
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`for`, `return`, `typedef`, `void`, `char`, `short`, `unsigned` and `long`;
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10 if `#include` and `#define` are counted.
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- The code helpfully declares "syntax_error!" right up front, filling the reader with confidence.
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- In spite of its inherent clarity, the code was presented to both *indent*(1) and
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*clang-format*(1), after running it through the preprocessor, sustaining its better qualities.
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- That the code is obfuscated is spelled out two different ways in the source; it helps
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to reformat the code to see the second spelling.
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- The author is overly fond of the code that handles input.
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There is no memory allocation, nor pre-allocation of arrays, so where does the
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memory come from? The multi-base strtol() code is pretty trick.
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No special attempt was made to replace operations with obscure mathematical relations,
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as the (lack of) beauty is in the parsing -- ask not where is the modulus operation,
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but how does it know when to mod -- okay, but where is add and subtract?
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And really, who doesn't enjoy a setjmp() in the argument list?
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- Finally, documentation of the source code structure is helpfully provided in rot13 format.
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But isn't it unsportsmanlike to rely upon it? However, even with this helpful guide,
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things like reading input lines remain as tricky to read as they are to write.
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Compiler warnings
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-----------------
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Calc is C99 compliant, and is ANSI/C90 compliant except for wanting 64-bit `long long`.
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Changing the two `long long` typedefs to `long`, and compiling with `gcc -m32`
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yields a program that operates on 32-bit values, with wrap-around of shifts mod 32:
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1<<48
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65536 0x00010000
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gcc 4.2.1 without arguments compiles cleanly (e.g. cc prog.c -o prog).
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This is my workaday compiler. gcc is also clean with -ansi, and -std=c99.
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clang 3.6.0 lives up to its namesake, resounding on non-problems.
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To stifle these complaints:
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-Wno-return-type -Wno-parentheses -Wno-empty-body
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When invoked with -ansi -pedantic, there are two warnings, which can be ignored:
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* `ISO C90 does not support 'long long'`
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With -Wall -std=c99, both are quite noisy, and all can be ignored:
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* `array subscript has type 'char' [-Wchar-subscripts]`
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* `value computed is not used [-Wunused-value]`
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* `operation on 'j' may be undefined [-Wsequence-point]`
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Test Suite
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----------
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If the program name begins with an "e", it echoes stdin to stdout.
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This allows for a convenient test suite:
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ln -s prog eprog
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PATH=. eprog < test.in | diff - test.out
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Spoilers
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--------
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If you do not want to puzzle out how it works, see spoilers.markdown.
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--------------------------------------------------------------------------------
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<!--
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(c) Copyright 1984-2016, [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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