SMHasher setup? - testing

Question

The SMHasher test suite for hash functions is touted as the best of the lot. But the latest version I've got (from rurban) gives absolutely no clue on how to check your proposed hash function (it does include an impressive battery of hash functions, but some of interest --if only for historic value-- are missing). Add that I'm a complete CMake newbie.

Answer 1

It's actually quite simple. You just need to install CMake.
Building SMHasher
To build SMHasher on a Linux/Unix machine:
git clone https://github.com/rurban/smhasher
cd smhasher/
git submodule init
git submodule update
cmake .
make
Adding a new hash function
To add a new function, you can edit just three files: Hashes.cpp, Hashes.h and main.cpp.
For example, I will add the ElfHash:
unsigned long ElfHash(const unsigned char *s)
{
unsigned long h = 0, high;
while (*s)
{
h = (h << 4) + *s++;
if (high = h & 0xF0000000)
h ^= high >> 24;
h &= ~high;
}
return h;
}
First, need to modify it slightly to take a seed and length:
uint32_t ElfHash(const void *key, int len, uint32_t seed)
{
unsigned long h = seed, high;
const uint8_t *data = (const uint8_t *)key;
for (int i = 0; i < len; i++)
{
h = (h << 4) + *data++;
if (high = h & 0xF0000000)
h ^= high >> 24;
h &= ~high;
}
return h;
}
Add this function definition to Hashes.cpp. Also add the following to Hashes.h:
uint32_t ElfHash(const void *key, int len, uint32_t seed);
inline void ElfHash_test(const void *key, int len, uint32_t seed, void *out) {
*(uint32_t *) out = ElfHash(key, len, seed);
}
In file main.cpp add the following line into array g_hashes:
{ ElfHash_test, 32, 0x0, "ElfHash", "ElfHash 32-bit", POOR, {0x0} },
(The third value is self-verification. You will learn this only after running the test once.)
Finally, rebuild and run the test:
make
./SMHasher ElfHash
It will show you all the tests that this hash function fails. (It is very bad.)