gistfile1.rb

# Compile CityHash
#g++ -shared city.cc -o libcity.dylib
#

# Figure out the symbol names.. this doesn't look right. Probably user error.
# nm -g libcity.dylib 
#
=begin
0000000000000db7 T __Z10CityHash64PKcm
0000000000001800 T __Z11CityHash128PKcm
...
0000000000001a55 T __ZSt9make_pairIyyESt4pairIT_T0_ES1_S2_
000000000000114e T __Z18CityHash64WithSeedPKcmy
000000000000117f T __Z19CityHash128WithSeedPKcmSt4pairIyyE

                 U ___gxx_personality_v0
                 U dyld_stub_binder
=end

module CityHash
  require "rubygems"
  require "ffi"
  extend FFI::Library
  ffi_lib "city"

  attach_function :_Z10CityHash64PKcm,  [:string, :size_t], :uint64
  attach_function :_Z11CityHash128PKcm, [:string, :size_t], :ulong
  attach_function :_Z18CityHash64WithSeedPKcmy, [:string, :size_t, :ulong], :ulong
end

if __FILE__ == $0
  require "benchmark"
  require "zlib"

  str = ''
  # You can preseed the CityHash functions
  seed = 1_100_200_300_400.1

  # Build a large-ish string
  
  100.times{str << (("A".."Z").to_a + (0..9).to_a).flatten.join}
  size = str.size
  puts "=======TO HASH=========="
  puts str
  puts "=======TO HASH=========="

  Benchmark.bmbm do |x|
    x.report("cityhash64")  { 10_000.times{CityHash._Z10CityHash64PKcm(str, size)} }
    x.report("cityhash128") { 10_000.times{CityHash._Z11CityHash128PKcm(str, size)} }
    x.report("cityhash64 (w/ seed)") { 10_000.times{CityHash._Z18CityHash64WithSeedPKcmy(str, size, seed)} }
    x.report("string#hash") { 10_000.times{str.hash}  }
    x.report("Zlib#crc32") { 10_000.times{ Zlib.crc32(str) } }
  end
  puts
  puts "Ruby Version is #{RUBY_VERSION}"
  puts "City Hash (64):    " + CityHash._Z10CityHash64PKcm(str, size).to_s
  puts "City Hash (128):   " + CityHash._Z11CityHash128PKcm(str, size).to_s
  # the String#hash value changes everytime you run the script (???)
  puts "String#hash:       " + str.hash.to_s
  puts "Zlib#crc32         " + Zlib.crc32(str).to_s
end

Does _Z11CityHash128PKcm work ok? What ffi and ruby version are you using? Because it crushes for me :(

Ruby 1.9.2 and latest FFI version. Those weird method names are the result of running 'nm -g libcity.dylib ' and inspecting the dumped symbols. do you get the same symbols?

Actually, I've added

extern "C"

before these functions and now can use it with normal names. But I've tried without extern "C' stuff too and it still crushes .