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<chapter id="regress">

<title id="regress-title">Regression Tests</title>

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

acrossplatforms, 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

expected by the current <productname>PostgreSQL</productname>

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>