pgsql: Simplify hash_xlog_split_allocate_page()

Simplify hash_xlog_split_allocate_page()

Instead of complicated pointer arithmetic, overlay a uint32 array and
just access the array members.  That's safe thanks to
XLogRecGetBlockData() returning a MAXALIGNed buffer.

Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/aSQy2JawavlVlEB0%40ip-10-97-1-34.eu-west-3.compute.internal

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/35988b31db7767ba446009611b9928add1d40f98

Modified Files
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src/backend/access/hash/hash_xlog.c | 35 +++++++++++++++++------------------
1 file changed, 17 insertions(+), 18 deletions(-)