[Issue 18921] New: make core.internal.hash cater to memberwise hash chaining

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18921

          Issue ID: 18921
           Summary: make core.internal.hash cater to memberwise hash
                    chaining
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: n8sh.secondary at hotmail.com

For use in memberwise hashing of structs (as in issue #18918) or in hashing
arrays, speed up the hashing of individual scalars.

Right now, for a `struct` where each field is `uint`, memberwise chained
hashing has a 250% speed penalty with LDC2 and a 350% speed penalty on DMD2
compared to treating the struct as an array of bytes. This seems fairly
constant regardless of the size of the struct.

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