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Update discussion of floating-point problems in regression tests.

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Tom Lane 2002-11-08 20:26:12 +00:00
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commit f2ef470196
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doc/src/sgml/regress.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/regress.sgml,v 1.29 2002/10/12 16:31:55 petere Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/regress.sgml,v 1.30 2002/11/08 20:26:12 tgl Exp $ -->
<chapter id="regress">
<title id="regress-title">Regression Tests</title>
@ -264,14 +264,19 @@ PGTZ='PST8PDT7,M04.01.0,M10.05.03'; export PGTZ
Some of the tests involve computing 64-bit (<type>double
precision</type>) numbers from table columns. Differences in
results involving mathematical functions of <type>double
precision</type> columns have been observed. The float8 and
geometry tests are particularly prone to small differences across
platforms, or even with different compiler optimization options.
precision</type> columns have been observed. The <literal>float8</> and
<literal>geometry</> tests are particularly prone to small differences
across platforms, or even with different compiler optimization options.
Human eyeball comparison is needed to determine the real
significance of these differences which are usually 10 places to
the right of the decimal point.
</para>
<para>
Some systems display minus zero as <literal>-0</>, while others
just show <literal>0</>.
</para>
<para>
Some systems signal errors from <function>pow()</function> and
<function>exp()</function> differently from the mechanism
@ -279,32 +284,6 @@ PGTZ='PST8PDT7,M04.01.0,M10.05.03'; export PGTZ
code.
</para>
</sect2>
<sect2>
<title>Polygon differences</title>
<para>
Several of the tests involve operations on geographic data about
the Oakland/Berkeley, California street map. The map data is expressed as
polygons whose vertices are represented as pairs of <type>double
precision</type> numbers (decimal latitude and
longitude). Initially, some tables are created and loaded with
geographic data, then some views are created that join two
tables using the polygon intersection operator
(<literal>##</literal>), then a select is done on the view.
</para>
<para>
When comparing the results from different platforms, differences
occur in the 2nd or 3rd place to the right of the decimal
point. The SQL statements where these problems occur are the
following:
<programlisting>
SELECT * from street;
SELECT * from iexit;
</programlisting>
</para>
</sect2>
<sect2>
<title>Row ordering differences</title>