Consistent String#hash based only on the string's content

Question

GOAL: Map every URL handled by a server to 0, 1, 2, or 3, distributing as uniformly as possible.

While the documentation for ruby\'s String#hash met

Answer 1

The easiest (and consistent) way may be this (and it's fast):

"https://www.example.com/abc/def/123?hij=345".sum % 4

That will always produce an integer 0 - 3, is quite fast, and should be fairly well distributed (though I haven't actually run tests on distribution).

Answer 2

There is tiny library xxHash:

XXhash.xxh32('qwe') #=> 2396643526
XXhash.xxh64('qwe') #=> 9343136760830690622

Maybe it will have more collisions but it is 10x faster than SHA1:

Benchmark.bm do |x|
  n = 100_000
  str = 'qweqweqwe'
  x.report('xxhash32') { n.times { XXhash.xxh32(str) } }
  x.report('xxhash64') { n.times { XXhash.xxh64(str) } }
  x.report('hexadigest') { n.times { Digest::SHA1.hexdigest(str) } }
end;1

#       user     system      total        real
# xxhash32  0.020000   0.000000   0.020000 (  0.021948)
# xxhash64  0.040000   0.000000   0.040000 (  0.036340)
# hexadigest  0.240000   0.030000   0.270000 (  0.276443)

Answer 3

there are lot of such functionality in ruby's digest module: http://ruby-doc.org/stdlib/libdoc/digest/rdoc/index.html

simple example:

require 'digest/sha1'
Digest::SHA1.hexdigest("some string")

Answer 4

You can try to_i(36).

"Hash me please :(".to_i(36)
=> 807137