Merge pull request #7 from lawrencegripper/lg/sqid-perf

Speedier `Sqids.new` 🦑

README.md

@@ -86,6 +86,11 @@ id = sqids.encode([1, 2, 3]) # 'se8ojk'
 numbers = sqids.decode(id) # [1, 2, 3]
 ```
 
+> [!WARNING]  
+> If you provide a large custom blocklist and/or custom alphabet, calls to `Sqid.new` can take 
+> ~1ms. You should create a singleton instance of `Sqid` at service start and reusing that rather than
+> repeatedly calling `Squid.new`
+
 ## 📝 License
 
 [MIT](LICENSE)

lib/sqids.rb

@@ -29,9 +29,19 @@ def initialize(options = {})
             "Minimum length has to be between 0 and #{min_length_limit}"
     end
 
-    filtered_blocklist = blocklist.select do |word|
-      word.length >= 3 && (word.downcase.chars - alphabet.downcase.chars).empty?
-    end.to_set(&:downcase)
+    filtered_blocklist = if blocklist == DEFAULT_BLOCKLIST && alphabet == DEFAULT_ALPHABET
+                           # If the blocklist is the default one, we don't need to filter it
+                           # we already know it's valid (lowercase and words longer than 3 chars)
+                           blocklist
+                         else
+                           # Downcase the alphabet once, rather than in the loop, to save significant time
+                           # with large blocklists
+                           downcased_alphabet = alphabet.downcase.chars
+                           # Filter the blocklist
+                           blocklist.select do |word|
+                             word.length >= 3 && (word.downcase.chars - downcased_alphabet).empty?
+                           end.to_set(&:downcase)
+                         end
 
     @alphabet = shuffle(alphabet)
     @min_length = min_length