pgsql: Improve performance of float overflow checks in btree_gist

Improve performance of float overflow checks in btree_gist

The current code could do unnecessary calls to isinf() (two for the
argument values all the time while one could be sufficient in some
cases).  zero_is_valid was never used but the result value was still
checked on 0 in the first position of the check.

This is similar to 607f8ce.  btree_gist has just copy-pasted the code
doing those checks from the backend float4/8 code, as of the macro
CHECKFLOATVAL(), to do the work.

Author: Haiying Tang
Discussion: https://postgr.es/m/OS0PR01MB611358E3A7BC3C2F874AC36BFBF39@OS0PR01MB6113.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/32cf7f7acce3891cbc3de53327704372bdd36d38

Modified Files
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contrib/btree_gist/btree_float4.c    |  4 +++-
contrib/btree_gist/btree_float8.c    |  8 +++++---
contrib/btree_gist/btree_utils_num.h | 17 -----------------
3 files changed, 8 insertions(+), 21 deletions(-)