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2015/hou/README.md

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+# Most Well-rounded Hash
+
+Qiming Hou <hqm03ster@gmail.com>  
+<http://www.houqiming.net/>  
+
+
+## Judges' comments:
+### To use:
+
+    make
+    
+    echo IOCCC | ./prog
+
+### Try:
+
+    echo "" | ./prog
+
+### Selected Judges Remarks:
+
+A good start for understanding this entry might be
+https://www.ietf.org/rfc/rfc1321.txt. How does it compute this using only a
+single looping construct? The original reference source code for this
+algorithm is about 355 lines of code, yet this entry is only 199 lines with
+one statement per line and it isn't using lots of macro expansion tricks like
+the reference code!
+
+Some things that make you go, "huh?"
+
+	./prog < prog.c | cut -c-5
+	./prog < Makefile | cut -c-4
+
+How are those values magically returned?
+
+What happens with a large file? Something over 256K
+
+	./prog < large_file
+
+Where does that message come from?
+
+
+## Author's comments:
+This looks like a normal C program.
+
+Almost everything is a double.
+
+There are tell-tale signs like `pow(2,(?/12))` and `exp(-?*?)` (names redacted). You can also find a bunch of cosines and polynomial evaluations.
+
+It looks like a ????? ???????????, right?
+
+Run and find out.
+
+### Why obfuscated
+
+Some poor scripting folks only have access to doubles (Jav?script, L?a, BA?IC, etc.).
+
+As a C programmer, I feel obliged to show a gesture of sympathy, to experience their pain and provide an answer.
+
+Except when absolutely necessary (`printf`, `int main()`, array indexing), there isn't a single integer. Even `getchar()` and `EOF` are immediately converted.
+
+Since `bool` counts as an integer type too, there is no boolean either. No comparison, no `if`, no `?:`, no `||` `&&`. Everything is done in a single loop that terminates on printf. Straight up arithmetic.
+
+`floor` and `ceil` are technically double-to-double functions, but they feel like cheating. Yes `cos`, no `floor`.
+
+### Limitations
+
+Hard requirements:
+
+* The platform must implement the `double` type as IEEE754-compliant 64-bit floating point numbers.  The 80-bit intermediate format used by x87 is considered as an violation of this. The code should print an error message on such platforms.
+
+* The program must start with the CPU / FPU in round-to-nearest mode.
+
+Soft requirements:
+
+* The compiler must respect `volatile`. The code is formatted to warn about that, though.
+
+* The printed result is only correct on little-endian machines. The program takes care to warn about this issue after printing an incorrect big-endian result. Error messages become garbled, though.
+
+Tested platforms:
+
+* Linux 3.18.7, Rasperberry Pi 2, clang 3.0-6.2, (works)
+* Linux 3.18.7, Rasperberry Pi 2, gcc 4.6.3, (works)
+* Mac OS X 10, x64, Apple LLVM version 6.1.0 (clang-602.0.53), (works)
+* Windows 8.1, x86, MSVC 2012 (works) 
+* Windows 8.1, x64, MSVC 2012 (works)
+* Windows 8.1, x86, MinGW gcc 4.6.2 (fails, prints error message)
+* Windows 8.1, x86, MinGW gcc 4.6.2 with -msse2 -mfpmath=sse (works)
+
+--------------------------------------------------------------------------------
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