Great thanks - we can take this to JIRAs now. I think it's worth changing the implementation of atanh if the test value just reflects what Spark does, and there's evidence is a little bit inaccurate. There's an equivalent formula which seems to have better accuracy.
On Fri, Jul 26, 2019 at 10:02 PM Takeshi Yamamuro <linguin....@gmail.com> wrote: > Hi, all, > > FYI: > >> @Yuming Wang the results in float8.sql are from PostgreSQL directly? > >> Interesting if it also returns the same less accurate result, which > >> might suggest it's more to do with underlying OS math libraries. You > >> noted that these tests sometimes gave platform-dependent differences > >> in the last digit, so wondering if the test value directly reflects > >> PostgreSQL or just what we happen to return now. > > The results in float8.sql.out were recomputed in Spark/JVM. > The expected output of the PostgreSQL test is here: > https://github.com/postgres/postgres/blob/master/src/test/regress/expected/float8.out#L493 > > As you can see in the file (float8.out), the results other than atanh > also are different between Spark/JVM and PostgreSQL. > For example, the answers of acosh are: > -- PostgreSQL > > https://github.com/postgres/postgres/blob/master/src/test/regress/expected/float8.out#L487 > 1.31695789692482 > > -- Spark/JVM > > https://github.com/apache/spark/blob/master/sql/core/src/test/resources/sql-tests/results/pgSQL/float8.sql.out#L523 > 1.3169578969248166 > > btw, the PostgreSQL implementation for atanh just calls atanh in math.h: > > https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/float.c#L2606 > > Bests, > Takeshi > >
