Re: Reducing the chunk header sizes on all memory context types - Mailing list pgsql-hackers

David Rowley <dgrowleyml@gmail.com> writes:
> Here's a patch which adds a comment to MemoryContextMethodID to Robert's patch.

OK, but while looking at that I noticed the adjacent

#define MEMORY_CONTEXT_METHODID_MASK \
    UINT64CONST((1 << MEMORY_CONTEXT_METHODID_BITS) - 1)

I'm rather astonished that that compiles; UINT64CONST was only ever
meant to be applied to *literals*.  I think what it's expanding to
is

    ((1 << MEMORY_CONTEXT_METHODID_BITS) - 1UL)

(or on some machines 1ULL) which only accidentally does approximately
what you want.  It'd be all right perhaps to write

    ((UINT64CONST(1) << MEMORY_CONTEXT_METHODID_BITS) - 1)

but you might as well avoid the Postgres-ism and just write

    ((uint64) ((1 << MEMORY_CONTEXT_METHODID_BITS) - 1))

Nobody's ever going to make MEMORY_CONTEXT_METHODID_BITS large
enough for the shift to overflow in int arithmetic.

            regards, tom lane