pgsql: Fix FPeq() and friends to get the right answers for infinities.

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pgsql: Fix FPeq() and friends to get the right answers for infinities.

Tom Lane-2
Fix FPeq() and friends to get the right answers for infinities.

"FPeq(infinity, infinity)" returned false, on account of getting NaN
when it subtracts the two inputs.  Fix that by adding a separate
check for exact equality.

FPle() and FPge() similarly got the wrong answer for two like-signed
infinities.  In those cases, we can just rearrange the comparisons
to avoid potentially subtracting infinities.

While the sibling functions FPne() etc accidentally gave the right
answers even with the internal NaN results, it seems best to make
similar adjustments to them to avoid depending on this.

FPeq() has to be converted to an inline function to avoid double
evaluations of its arguments, and I did the same for the others
just for consistency.

In passing, make the handling of NaN cases in line_eq() and
point_eq_point() simpler and easier to reason about, and perhaps
faster.

This results in just one visible regression test change: slope()
now gives DBL_MAX for two inputs of (inf,1e300), which is consistent
with what it does for (1e300,inf), so that seems like a bug fix.

Discussion: https://postgr.es/m/CAGf+fX70rWFOk5cd00uMfa__0yP+vtQg5ck7c2Onb-Yczp0URA@...

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8597a48d01b6cc0b09ff626253ac93c67e5516d5

Modified Files
--------------
src/backend/utils/adt/geo_ops.c        | 39 +++++++++++++----------
src/include/utils/geo_decls.h          | 57 +++++++++++++++++++++++++++++-----
src/test/regress/expected/geometry.out |  2 +-
3 files changed, 72 insertions(+), 26 deletions(-)