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Try to fix portability issue in enum renumbering (again).

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The hack embodied in commit 4ba61a487 no longer works after today's change
to allow DatumGetFloat4/Float4GetDatum to be inlined (commit 14cca1bf8).
Probably what's happening is that the faulty compilers are deciding that
the now-inlined assignment is a no-op and so they're not required to
round to float4 width.

We had a bunch of similar issues earlier this year in the degree-based
trig functions, and eventually settled on using volatile intermediate
variables as the least ugly method of forcing recalcitrant compilers
to do what the C standard says (cf commit 82311bcdd).  Let's see if
that method works here.

Discussion: <4640.1472664476@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-08-31 13:58:01 -04:00
parent 679226337a
commit 65a588b4c3
1 changed files with 14 additions and 12 deletions
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26
src/backend/catalog/pg_enum.c
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@@ -315,21 +315,21 @@ restart:
newelemorder = nbr_en->enumsortorder + 1;
else
{
other_nbr_en = (Form_pg_enum) GETSTRUCT(existing[other_nbr_index]);
newelemorder = (nbr_en->enumsortorder +
other_nbr_en->enumsortorder) / 2;
/*
* On some machines, newelemorder may be in a register that's
* wider than float4. We need to force it to be rounded to float4
* precision before making the following comparisons, or we'll get
* wrong results. (Such behavior violates the C standard, but
* fixing the compilers is out of our reach.)
* The midpoint value computed here has to be rounded to float4
* precision, else our equality comparisons against the adjacent
* values are meaningless. The most portable way of forcing that
* to happen with non-C-standard-compliant compilers is to store
* it into a volatile variable.
*/
newelemorder = DatumGetFloat4(Float4GetDatum(newelemorder));
volatile float4 midpoint;
if (newelemorder == nbr_en->enumsortorder ||
newelemorder == other_nbr_en->enumsortorder)
other_nbr_en = (Form_pg_enum) GETSTRUCT(existing[other_nbr_index]);
midpoint = (nbr_en->enumsortorder +
other_nbr_en->enumsortorder) / 2;
if (midpoint == nbr_en->enumsortorder ||
midpoint == other_nbr_en->enumsortorder)
{
RenumberEnumType(pg_enum, existing, nelems);
/* Clean up and start over */
@@ -337,6 +337,8 @@ restart:
ReleaseCatCacheList(list);
goto restart;
}
newelemorder = midpoint;
}
}