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Update (May 12, 2019)

  • Mum-hash version 3 has been released
  • Version 3 has faster hashing for small and long keys
    • Version 3 is default. To switch on version 1 or version 2, please define macro MUM_V1 or MUM_V2 before inclusion of mum.h
  • Version 3 has higher quality hashing comparing to version 2
    • Although version 2 passed all the tests of appleby-smhasher, it did not pass strict Avalanche tests of demerphq-smhasher
    • Version 3 fixed this problem and now version 3 (as version 1) passes all tests of demerphq-smhasher
  • Although I have a high quality x86_64 vectorized mum-hash implementation (using pmuludq256/pshufd256/pxo256) which achieves Meow hash speed on very long keys I decided not to add this implementation to version 3 as it complicates the code, makes code slower on targets not having analogous vector instructions, and as the speed of hashing long keys is rarely used for hash tables

Update (Apr 1, 2019)

  • Meow hash is updated to version 0.4
  • Benchmark results for x86-64 were updated

Update (Oct 31, 2018)

  • A new version of mum hash was created (version 2 or Halloween version)
  • The new version works faster for short keys which are a majority of hash table cases usages
  • The new version also passes all tests of SMHasher
  • The old version still can be used by definining macro MUM_V1 before compiling mum.h
    • When MUM_V1 is defined, you will get the same hashes as previously
  • The new version was also simplified by removing specialized code using features of x86-64 CPU with BMI2 flag
    • This has a tiny impact on mum hash performance
  • I posted performance results for more fresh CPUs (i7-8700K, Power9, and APM X-Gene CPU Potenza A3)
  • I also added performance results for a new hash, Meow hash
    • Meow hash is based on usage of x86-64 AES insns
    • Meow hash is the fastest hash for very long keys but it is not suitable for hash tables
      • Meow is too slow for most hash table cases
      • Meow can be used only for x86-64
      • Meow hash requires aligned data because AES insns needs aligned data
  • MUM PRNG performance was improved
    • A performance bug (preventing inlining of code specialized for different architectures) was fixed
  • MUM-512 performance was improved
    • The same performance bug was fixed but in a different way

MUM Hash

  • MUM hash is a fast non-cryptographic hash function suitable for different hash table implementations
  • MUM means MUltiply and Mix
    • It is a name of the base transformation on which hashing is implemented
    • Modern processors have a fast logic to do long number multiplications
    • It is very attractable to use it for fast hashing
      • For example, 64x64-bit multiplication can do the same work as 32 shifts and additions
    • I'd like to call it Multiply and Reduce. Unfortunately, MUR (MUltiply and Rotate) is already taken for famous hashing technique designed by Austin Appleby
    • I've chosen the name also as I am releasing it on Mother's day
  • MUM hash passes all SMHasher tests
    • For comparison, only 4 out of 15 non-cryptographic hash functions in SMHasher passes the tests, e.g. well known FNV, Murmur2, Lookup, and Superfast hashes fail the tests
  • MUM algorithm is simpler than City64 and Spooky ones
  • MUM is specifically designed to be fast for 64-bit CPUs (Sorry, I did not want to spend my time on dying architectures)
    • Still MUM will work for 32-bit CPUs and it will be sometimes faster Spooky and City
  • On x86-64 MUM hash is faster than City64 and Spooky on all tests except for one test for the bulky speed
    • Starting with 240-byte strings, City uses Intel SSE4.2 crc32 instruction
    • I could use the same instruction but I don't want to complicate the algorithm
    • In typical scenario, such long strings are rare. Usually another interface (see mum_hash_step) is used for hashing big data structures
  • MUM has a fast startup. It is particular good to hash small keys which are a majority of hash table applications

MUM implementation details

  • Input 64-bit data are randomized by 64x64->128 bit multiplication and mixing high- and low-parts of the multiplication result by using an addition. The result is mixed with the current state by using XOR
    • Instead of the addition for mixing high- and low- parts, XOR could be used
      • Using the addition instead of XOR improves performance by about 10% on Haswell and Power7
  • Prime numbers randomly generated with the equal probability of their bit values are used for the multiplication
  • When all primes are used once, the state is randomized and the same prime numbers are used again for subsequent data randomization
  • Major loop is transformed to be unrolled by compiler to benefit from the compiler instruction scheduling optimization and OOO instruction execution in modern CPUs
  • AARCH64 128-bit result multiplication is very slow as it is implemented by a GCC library function
    • To use only 2 insns for such multiplication one GCC asm extension was added

MUM benchmarking vs Spooky, City64, xxHash64, MetroHash64, MeowHash, and SipHash24

  • Here are the results of benchmarking MUM and the fastest non-cryptographic hash functions I know:
    • Google City64 (sources are taken from SMHasher)
    • Bob Jenkins Spooky (sources are taken from SMHasher)
    • Yann Collet's xxHash64 (sources are taken from the original repository)
  • Murmur hash functions are slower so I don't compare it here
  • I also added J. Aumasson and D. Bernstein's SipHash24 for the comparison as it is a popular choice for hash table implementation these days
  • A metro hash was added as people asked and as metro hash is claimed to be the fastest hash function
    • metro hash is not portable as others functions as it does not deal with unaligned accesses problem on some targets
    • metro hash will produce different hash for LE/BE targets
    • some people on hackernews pointed out that the algorithm is very close to xxHash one but still it is much faster xxHash
  • Measurements were done on 3 different architecture machines:
    • 4.7 GHz Intel i7-8700K
    • 3.8 GHz Power9
    • 2.4 GHz APM X-Gene CPU Potenza A3
  • Each test was run 3 times and the minimal time was taken
    • GCC-7.3.1 was used for Intel machine, GCC-8.2.1 was used AARCH64, and GCC-4.9 was used for Power9
    • -O3 was used for all compilations
    • The strings were generated by rand calls
    • The strings were aligned to see a hashing speed better and to permit runs for MeowHash and Metro
    • No constant propagation for string length is forced. Otherwise, the results for MUM hash would be even better
    • The best results in the table below are highlighted.
    • Some people complaint that my comparison is unfair as most hash functions are not inlined
      • I believe that the interface is the part of the implementation. So when the interface does not provide an easy way for inlining, it is an implementation pitfall
      • Still to address the complaints I added -flto for benchmarking all hash functions excluding MUM. This option makes cross-file inlining
      • xxHash64 results became worse for small strings and better for the bulk speed test
      • All results for other functions improved, sometimes quite a lot

Intel i7-9700K

  • Hashing 10,000 of 16MB strings
  • Hashing 1,280M strings for all other length strings
Spooky City xxHash SipHash24 Metro MeowHash MUM-V1 MUM-V2 MUM-V3
5-byte 6.62s 8.78s 6.80s 10.07s 5.76s 11.25s 6.57s 5.56s 4.85s
8-byte 6.30s 8.81s 6.54s 12.89s 4.18s 11.25s 4.74s 3.69s 2.88s
16-byte 12.64s 8.20s 8.11s 16.13s 5.71s 9.42s 5.85s 4.75s 3.95s
32-byte 13.20s 9.60s 11.60s 22.40s 11.72s 9.42s 6.83s 5.52s 4.71s
64-byte 19.40s 10.60s 12.86s 36.70s 12.53s 9.42s 9.35s 8.79s 6.54s
128-byte 32.58s 14.25s 15.49s 63.82s 14.63s 10.46s 13.64s 13.01s 11.53s
Bulk 9.74s 9.17s 9.59s 48.63s 8.89s 4.65s 10.33s 10.38s 7.93s

Power9 (3.8GHz)

Spooky City64 xxHash64 SipHash24 Metro64 MUM-V1 MUM-V2 MUM-V3
5 bytes 22.14s 23.87s 20.54s 45.06s 18.01s 18.44s 18.29s 17.29s
8 bytes 17.62s 23.68s 19.92s 54.13s 9.82s 9.18s 7.55s 6.00s
16 bytes 34.02s 18.60s 23.62s 61.19s 15.75s 17.32s 17.47s 16.46s
32 bytes 32.16s 21.66s 34.73s 75.72s 27.82s 18.72s 18.87s 17.93s
64 bytes 53.53s 23.40s 37.97s 104.23s 29.88s 21.34s 20.42s 20.29s
128 bytes 87.46s 33.17s 44.60s 193.19s 38.73s 32.96s 30.90s 27.47s
16MB 17.12s 13.64s 14.56s 116.85s 12.22s 11.59s 11.56s 10.69s

AARCH64 (APM X-Gene)

Spooky City64 xxHash64 SipHash24 Metro64 MUM-V1 MUM-V2 MUM-V3
5 bytes 18.13s 25.60s 22.40s 27.73s 18.67s 20.79s 16.00s 17.07s
8 bytes 17.60s 25.60s 21.33s 35.73s 13.33s 14.39s 11.20s 9.06s
16 bytes 30.93s 25.07s 26.13s 45.33s 17.07s 21.33s 15.99s 19.73s
32 bytes 30.94s 29.33s 36.27s 62.94s 36.27s 28.26s 24.00s 28.27s
64 bytes 44.80s 30.40s 40.54s 101.87s 38.40s 41.60s 37.34s 41.07s
128 bytes 73.07s 45.34s 49.07s 195.75s 43.74s 69.34s 64.54s 67.74s
16MB 40.01s 45.82s 53.24s 188.42s 53.25s 48.48s 48.48s 33.90s


  • A major loop in function _mum_hash_aligned can be vectorized using vector multiplication, addition, xor, and shuffle instructions
  • Modern x86-64 CPUs currently does not have vector multiplication 64 x 64-bit -> 128-bit (pclmulqdq only 1 64x64->128-bit multiplication)
  • AVX2 CPUs only have vector multiplication 32 x 32-bit -> 64-bit
    • One such vector instruction makes 4 multiplications which is roughly equivalent what two MULQ/MULX insns does
    • On very long keys, usage of such insn permits to achieve speed of Meow hash which is based on usage of AES insns
  • If Intel introduces a new vector insn for 64 x 64-bit -> 128-bit multiplication, potentially it could increase MUM speed up to 2 times (may be less as major memory speed access becomes a major bottleneck of the overall hash speed)
  • I decided not to use the vector insns because it makes mum-hash implementation complicated and less portable
  • I believe major application of non-cryptographic hash functions are hashing for hash tables and speed of hashing of short keys is the most important requirement for such application

Using cryptographic vs. non-cryptographic hash function

  • People worrying about denial attacks based on generating hash collisions started to use cryptographic hash functions in hash tables
  • Cryptographic functions are very slow
    • sha1 is about 20-30 slower than MUM and City on the bulk speed tests
    • The new fastest cryptographic hash function SipHash is up to 10 times slower
  • MUM is also resistant to preimage attack (finding a string with given hash)
    • To make hard moving to previous state values we use mostly 1-to-1 one way function lo(x*C) + hi(x*C) where C is a constant. Brute force solution of equation f(x) = a probably requires 2^63 tries. Another used function equation x ^ y = a has a 2^64 solutions. It complicates finding the overal solution further
  • If somebody is not convinced, you can use randomly chosen multiplication constants (see function mum_hash_randomize). Finding a string with a given hash even if you know a string with such hash probably will be close to finding two or more solutions of Diophantine equations
  • If somebody is still not convinced, you can implement hash tables to recognize the attack and rebuild the table using MUM function with the new multiplication constants
  • Analogous approach can be used if you use weak hash function as MurMur or City. Instead of using cryptographic hash functions all the time, hash tables can be implemented to recognize the attack and rebuild the table and start using a cryptographic hash function
  • This approach solves the speed problem and permits to switch easily to a new cryptographic hash function if a flaw is found in the old one, e.g. switching from SipHash to SHA2

How to use MUM

  • Please just include file mum.h into your C/C++ program and use the following functions:
    • optional mum_hash_randomize for choosing multiplication constants randomly
    • mum_hash_init, mum_hash_step, and mum_hash_finish for hashing complex data structures
    • mum_hash64 for hashing a 64-bit data
    • mum_hash for hashing any continuous block of data
  • To compare MUM speed with Spooky, City64, and SipHash24 on your machine go to the directory src and run a script
sh bench
  • The script will compile source files and run the tests printing the results

Crypto-hash function MUM512

  • MUM is not designed to be a crypto-hash
    • The key (seed) and state are only 64-bit which are not crypto-level ones
    • The result can be different for different targets (BE/LE machines, 32- and 64-bit machines) as for other hash functions, e.g. City (hash can be different on SSE4.2 nad non SSE4.2 targets) or Spooky (BE/LE machines)
      • If you need the same MUM hash independent on the target, please define macro MUM_TARGET_INDEPENDENT_HASH
  • There is a variant of MUM called MUM512 which can be a candidate for a crypto-hash function and keyed crypto-hash function and might be interesting for researchers
    • The key is 256-bit
    • The state and the output are 512-bit
    • The block size is 512-bit
    • It uses 128x128->256-bit multiplication which is analogous to about 64 shifts and additions for 128-bit block word instead of 80 rounds of shifts, additions, logical operations for 512-bit block in sha2-512.
  • It is only a candidate for a crypto hash function
    • I did not make any differential crypto-analysis or investigated probabilities of different attacks on the hash function (sorry, it is too big job)
      • I might be do this in the future as I am interesting in differential characteristics of the MUM512 base transformation step (128x128-bit multiplications with addition of high and low 128-bit parts)
      • I am interesting also in the right choice of the multiplication constants
      • May be somebody will do the analysis. I will be glad to hear anything. Who knows, may be it can be easily broken as Nimbus cipher.
    • The current code might be also vulnerable to timing attack on systems with varying multiplication instruction latency time. There is no code for now to prevent it
  • To compare the MUM512 speed with the speed of SHA-2 (SHA512) and SHA-3 (SHA3-512) go to the directory src and run a script sh bench-crypto
    • SHA-2 and SHA-3 code is taken from RHash
  • Blake2 crypto-hash from was added for comparison. I use sse version of 64-bit Blake2 (blake2b).
  • Here is the speed of the crypto hash functions on 4.7 GHz Intel i7-8700K:
MUM512 SHA2 SHA3 Blake2B
10 bytes (20 M texts) 0.57s 0.53s 0.87s 0.68s
100 bytes (20 M texts) 0.77s 0.51s 1.68s 0.68s
1000 bytes (20 M texts) 2.75s 3.79s 11.58s 2.85s
10000 bytes (5 M texts) 5.60s 9.21s 28.37s 6.23s

Pseudo-random generators

  • Files mum-prng.h and mum512-prng.h provides pseudo-random functions based on MUM and MUM512 hash functions
  • All PRNGs passed NIST Statistical Test Suite for Random and Pseudorandom Number Generators for Cryptographic Applications (version 2.2.1) with 1000 bitstreams each containing 1M bits
    • Although MUM PRNG pass the test, it is not a cryptographically secure PRNG as the hash function used for it
  • To compare the PRNG speeds go to the directory src and run a script sh bench-prng
  • For the comparison I wrote crypto-secured Blum Blum Shub PRNG (file bbs-prng.h) and PRNGs based on fast cryto-level hash functions in ChaCha stream cipher (file chacha-prng.h) and SipHash24 (file sip24-prng.h).
    • The additional PRNGs also pass the Statistical Test Suite
  • For the comparison I also added the fastest PRNGs
  • I had no intention to tune MUM based PRNG first but after adding xoroshiro128+ and finding how fast it is, I've decided to speedup MUM PRNG
    • I added code to calculate a few PRNs at once to calculate them in parallel
    • I added AVX2 version functions to use faster MULX instruction
    • The new version also passed NIST Statistical Test Suite. It was tested even on bigger data (10K bitstreams each containing 10M bits). The test took several days on i7-4790K
    • The new version is almost 2 times faster the old one and MUM PRN speed became almost the same as xoroshiro/xoshiro ones
      • All xoroshiro/xoshiro and MUM PRNG functions are inlined in the benchmark program
      • both code without inlining will be visibly slower and the speed difference will be negligible as one PRN calculation takes only about 3-4 machine cycle for xoroshiro/xoshiro and MUM PRN.
  • Update Nov. 2: I found that MUM PRNG fails practrand on 512GB. So I modified it. Instead of basically 16 independent PRNGs with 64-bit state, I made it one PRNG with 1024-bit state. I also managed to speed up MUM PRNG by 15%.
    • There was a typo in XOSHIRO512** performance result (it was 1944 M prns/sec). So I fixed it. It is actually 1044.
  • All PRNG were tested by practrand with 4TB PRNG generated stream (it took a few days)
    • GLIBC RAND, xoroshiro128+, xoshiro256+, and xoshiro512+ failed on the first stages of practrand
    • the rest PRNGs passed
    • BBS PRNG was tested by only 64GB stream because it is too slow
  • Here is the speed of the PRNGs in millions generated PRNs per second on 4.7 GHz Intel i7-8700K:
M prns/sec
BBS 0.078
ChaCha 199
SipHash24 413
MUM512 83
MUM 1317
XOSHIRO128** 1130
XOSHIRO256** 1337
XOSHIRO512** 1044
XOROSHIRO128+ 1342
XOSHIRO256+ 1339
XOSHIRO512+ 1253
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