more prep work for jRuby

Gemfile

@@ -49,9 +49,10 @@ gem 'message_bus'
 
 gem 'rails_multisite'
 
-gem 'fast_xs'
+gem 'fast_xs', platform: :mri
 
-gem 'fast_xor'
+# may move to xorcist post: https://github.com/fny/xorcist/issues/4
+gem 'fast_xor', platform: :mri
 
 gem 'fastimage'
 
@@ -141,7 +142,7 @@ end
 # this is an optional gem, it provides a high performance replacement
 # to String#blank? a method that is called quite frequently in current
 # ActiveRecord, this may change in the future
-gem 'fast_blank'
+gem 'fast_blank', platform: :mri
 
 # this provides a very efficient lru cache
 gem 'lru_redux'
@@ -155,7 +156,7 @@ gem 'htmlentities', require: false
 gem 'flamegraph', require: false
 gem 'rack-mini-profiler', require: false
 
-gem 'unicorn', require: false
+gem 'unicorn', require: false, platform: :mri
 gem 'puma', require: false
 gem 'rbtrace', require: false, platform: :mri
 gem 'gc_tracer', require: false, platform: :mri

lib/pbkdf2.rb

@@ -31,7 +31,7 @@ class Pbkdf2
 
   # fallback xor in case we need it for jruby ... way slower
   def self.xor(x, y)
-    x.bytes.zip(y.bytes).map { |x, y| x ^ y }.pack('c*')
+    x.bytes.zip(y.bytes).map { |a, b| a ^ b }.pack('c*')
   end
 
   def self.prf(hash_function, password, data)