Two different hashing algorithms are implemented, FastHash and MurmurHash3, but only the FastHash is used by the sketch algorithms.

Hash Functions

FastHash

An implementation of both the 32-bit and 64-bit versions of the FastHash algorithm implemented and checked against the C++ version found at https://github.com/rurban/smhasher/blob/master/fasthash.cpp. The FastHash64 is used extensively throughout sketchnu. Both functions take bytes and a seed value and return an unsigned integer of 32 or 64-bits. The 32-bit version first calls the 64-bit version and then does some bit mixing to reduce down to 32-bit.

Usage

The FastHash functions take in bytes and return unsigned integers:

from sketchnu.hashes import fasthash64, fasthash32
hv_64 = fasthash64(b'one_key', 0)
hv_32 = fasthash32(b'one_key', 1)

Testing

Compare the fasthash32 against the smhasher C++ version. Since the fasthash32() calls fasthash64() and then does some bit mixing, by testing the fasthash32() we are also testing the fasthash64().

Values we assert against are from running the C++ version with the given keys and seeds. C++ code was taken from https://github.com/rurban/smhasher/blob/master/fasthash.cpp https://github.com/rurban/smhasher/blob/master/fasthash.h

MurmurHash3

An implementation of the 32-bit version of the MurmurHash3 algorithm implemented and checked against the C++ version found at https://github.com/rurban/smhasher/blob/master/MurmurHash3.cpp

Usage

The murmur3 function takes in bytes and returns unsigned 32-bit integer:

from sketchnu.hashes import murmur3
hv = murmur3(b'one_key', 0)

Testing

Compare the murmur3 against the smhasher C++ version found in the MurmurHash3_x86_32() function.

Values we assert against are from running the C++ version with the given keys and seeds. C++ code was taken from https://github.com/rurban/smhasher/blob/master/MurmurHash3.cpp https://github.com/rurban/smhasher/blob/master/MurmurHash3.h