improve performance and memory usage in HashUtils.djb2 (#376)

#28

"""
Runtime profiling indicates this method generates several many memory
allocations.

Comparing to the JS implementation, we saw the intent of the `hash &=
hash` line was to force the JS runtime to keep the number as a 32-bit
integer. This is indeed the correct way to do it in JS, but not in Ruby;
as a result, the `hash` local will grow ever larger, requiring more and
more memory since Ruby supports unbounded integers.

Fix: truncate the hash value on each iteration with the same 32-bit
`0xFFFFFFF` constant used at the end instead.
"""

Co-authored-by: Sam Kimbrel <[email protected]>

Author: tore-statsig

lib/hash_utils.rb

@@ -9,7 +9,7 @@ def self.djb2(input_str)
       hash = 0
       input_str.each_char.each do |c|
         hash = (hash << 5) - hash + c.ord
-        hash &= hash
+        hash &= 0xFFFFFFFF
       end
       hash &= 0xFFFFFFFF # Convert to unsigned 32-bit integer
       return hash.to_s