[Issue 19072] Object.toHash and typeid(void*).getHash(&ptr) should be more varied in their low bits

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19072

--- Comment #1 from github-bugzilla at puremagic.com ---
Commits pushed to master at https://github.com/dlang/druntime

https://github.com/dlang/druntime/commit/710adf3f5d7d15f6024266a584de8ab1feb84fb3
Fix Issue 19072 - Object.toHash and typeid(void*).getHash(&ptr) should be more
varied in their low bits

The low bits of Object.toHash are insufficiently varied. Depending on
the platform the bottom 4, 3, or 2 bits of the result will always be
zero. This is bad because the low bits of a hash code are typically the
most significant for hashtable implementations. D's builtin AA deals
with this and other potential defects by rehashing the hash codes it
receives. Some 3rd party hashtable implementations do the same, but
others assume that keys with a defined toHash have reasonable hashcodes
that can be used without need for further mixing.

Fixing this is not hard and not computationally expensive. This PR also
does a similar thing for raw pointers. Although it will not always be
necessary for them the cost is low and it will frequently be a benefit.

https://github.com/dlang/druntime/commit/b70774bc00a8e837eef05bbd2680ddc2fb2d62ea
Merge pull request #2247 from n8sh/object-hash-19072

Fix Issue 19072 - Object.toHash and typeid(void*).getHash(&ptr) should be more
varied in their low bits
merged-on-behalf-of: Petar Kirov <ZombineDev at users.noreply.github.com>

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