Initial working code

Author: skeeto

.gitignore

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+prospector

Makefile

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+CC     = cc
+CFLAGS = -std=c99 -Wall -Wextra -march=native -O3 -ggdb3
+
+prospector: prospector.c
+	$(CC) $(LDFLAGS) $(CFLAGS) -o $@ prospector.c $(LDLIBS)
+
+clean:
+	rm -f prospector

README.md

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+# Hash Function Prospector
+
+This is a little tool for automated [integer hash function][wang]
+discovery. It generates billions of [integer hash functions][jenkins] at
+random from a selection of [nine reversible operations][rev]. The
+generated functions are JIT compiled and their avalanche behavior is
+evaluated. The current best function is printed out in C syntax.
+
+The *avalanche score* is the number of output bits that remain "fixed"
+on average when a single input bit is flipped. Lower scores are better.
+Ideally the score is 0 — e.g. every output bit flips with a 50% chance
+when a single input bit is flipped.
+
+Prospector can generate both 32-bit and 64-bit integer hash functions.
+Check the usage (`-h`) for the full selection of options. Due to the JIT
+compiler, only x86-64 is supported, though the functions it discovers
+can, of course, be used anywhere.
+
+## Discovered Functions
+
+So far I've used prospector to discover these two high quality 32-bit
+integer hash functions:
+
+```c
+/* Avalanche score = 1.83
+ * Compiles to only 23 bytes on x86-64
+ * High avalanche
+ * 6 billion hashes / second (Haswell)
+ */
+uint32_t
+mosquito32(uint32_t x)
+{
+    x  = ~x;
+    x ^= x >> 16;
+    x *= UINT32_C(0xb03a22b3);
+    x ^= x >> 10;
+    return x;
+}
+
+/* Avalanche score = 1.51
+ * Very effective avalanche
+ * 3.3 billion hashes / second (Haswell)
+ */
+uint32_t
+skeeto32(uint32_t x)
+{
+    x  = ~x;
+    x ^= x >> 2;
+    x += x << 21;
+    x ^= x >> 15;
+    x ^= x << 5;
+    x ^= x >> 9;
+    x ^= x << 13;
+    return x;
+}
+```
+
+## Reversible operation selection
+
+```c
+x  = ~x;
+x ^= constant;
+x *= constant; // only odd constants
+x += constant;
+x ^= x >> constant;
+x ^= x << constant;
+x += x << constant;
+x -= x << constant;
+x = (x << constant) | (x >> (nbits - constant));
+```
+
+Technically `x = ~x` is covered by `x = ^= constant`. However, `~x` is
+uniquely special and particularly useful. The generator is very unlikely
+to generate the one correct constant for the XOR operator that achieves
+the same effect.
+
+
+[rev]: http://papa.bretmulvey.com/post/124027987928/hash-functions
+[wang]: https://gist.github.com/badboy/6267743
+[jenkins]: http://burtleburtle.net/bob/hash/integer.html

UNLICENSE

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+This is free and unencumbered software released into the public domain.
+
+Anyone is free to copy, modify, publish, use, compile, sell, or
+distribute this software, either in source code form or as a compiled
+binary, for any purpose, commercial or non-commercial, and by any
+means.
+
+In jurisdictions that recognize copyright laws, the author or authors
+of this software dedicate any and all copyright interest in the
+software to the public domain. We make this dedication for the benefit
+of the public at large and to the detriment of our heirs and
+successors. We intend this dedication to be an overt act of
+relinquishment in perpetuity of all present and future rights to this
+software under copyright law.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
+
+For more information, please refer to <http://unlicense.org/>