Performance: Reduce the time complexity of all Faker::Crypto methods (#2938)

* Reduce the time complexity of all Faker::Crypto methods

* Store crypto lorem number of characters in a class constant

Author: alextaujenis

lib/faker/default/crypto.rb

@@ -5,6 +5,15 @@
 module Faker
   class Crypto < Base
     class << self
+      # Setting the lorem character number lower than the default of
+      # 255 reduces the time complexity of each hash algorithm while
+      # still returning deterministically unique values. See
+      # https://github.com/faker-ruby/faker/pull/2938 for more info.
+      MD5_MIN_NUMBER_OF_CHARACTERS = 25
+      SHA1_MIN_NUMBER_OF_CHARACTERS = 31
+      SHA256_MIN_NUMBER_OF_CHARACTERS = 50
+      SHA512_MIN_NUMBER_OF_CHARACTERS = 100
+
       ##
       # Produces an MD5 hash.
       #
@@ -15,7 +24,7 @@ class << self
       #
       # @faker.version 1.6.4
       def md5
-        OpenSSL::Digest::MD5.hexdigest(Lorem.characters)
+        OpenSSL::Digest::MD5.hexdigest(Lorem.characters(number: MD5_MIN_NUMBER_OF_CHARACTERS))
       end
 
       ##
@@ -28,7 +37,7 @@ def md5
       #
       # @faker.version 1.6.4
       def sha1
-        OpenSSL::Digest::SHA1.hexdigest(Lorem.characters)
+        OpenSSL::Digest::SHA1.hexdigest(Lorem.characters(number: SHA1_MIN_NUMBER_OF_CHARACTERS))
       end
 
       ##
@@ -41,7 +50,7 @@ def sha1
       #
       # @faker.version 1.6.4
       def sha256
-        OpenSSL::Digest::SHA256.hexdigest(Lorem.characters)
+        OpenSSL::Digest::SHA256.hexdigest(Lorem.characters(number: SHA256_MIN_NUMBER_OF_CHARACTERS))
       end
 
       ##
@@ -54,7 +63,7 @@ def sha256
       #
       # @faker.version next
       def sha512
-        OpenSSL::Digest::SHA512.hexdigest(Lorem.characters)
+        OpenSSL::Digest::SHA512.hexdigest(Lorem.characters(number: SHA512_MIN_NUMBER_OF_CHARACTERS))
       end
     end
   end