Commits on Aug 15, 2023

1. ruby: Fix object cache lookups on 32-bit platforms (#13494) …

   #13204 refactored the Ruby object cache to use a key of `LL2NUM(key_val)` instead of `LL2NUM(key_val >> 2)`. On 32-bit systems, `LL2NUM(key_val)` returns inconsistent results because a large value has to be stored as a Bignum on the heap. This causes cache lookups to fail.
   
   This commit restores the previous behavior of using `ObjectCache_GetKey`, which discards the lower 2 bits, which are zero. This enables a key to be stored as a Fixnum on both 32 and 64-bit platforms.
   
   As https://patshaughnessy.net/2014/1/9/how-big-is-a-bignum describes, a Fixnum uses:
   
   * 1 bit for the `FIXNUM_FLAG`.
   * 1 bit for the sign flag.
   
   Therefore the largest possible Fixnum value on a 64-bit value is 4611686018427387903 (2^62 - 1). On a 32-bit system, the largest value  is 1073741823 (2^30 - 1).
   
   For example, a possible VALUE pointer address on a 32-bit system:
   
   0xff5b4af8 => 4284173048
   
   Dropping the lower 2 bits makes up for the loss of range to these flags. In the example above, we see that shifting by 2 turns the value into a 30-bit number, which can be represented as a Fixnum:
   
   (0xff5b4af8 >> 2) => 1071043262
   
   This bug can also manifest on a 64-bit system if the upper bits are 0xff.
   
   Closes #13481
   
   Closes #13494
   
   COPYBARA_INTEGRATE_REVIEW=#13494 from stanhu:sh-fix-ruby-protobuf-32bit d63122a
   FUTURE_COPYBARA_INTEGRATE_REVIEW=#13494 from stanhu:sh-fix-ruby-protobuf-32bit d63122a
   PiperOrigin-RevId: 557216800

   

   stanhu authored and Copybara-Service committed Aug 15, 2023
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