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Make FLOAT(p) measure the precision p in bits, not decimal digits, to

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match the SQL standard.  Document FLOAT and FLOAT(p) notations in
datatype.sgml.  Per recent pghackers discussion.
This commit is contained in:
Tom Lane
2003-06-17 23:12:36 +00:00
parent 596652d6eb
commit eab5d643b2
3 changed files with 44 additions and 12 deletions
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41
doc/src/sgml/datatype.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.116 2003/03/13 01:30:27 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.117 2003/06/17 23:12:36 tgl Exp $
-->
<chapter id="datatype">
@ -607,16 +607,47 @@ NUMERIC
</para>
<para>
Normally, the <type>real</type> type has a range of at least
-1E+37 to +1E+37 with a precision of at least 6 decimal digits. The
<type>double precision</type> type normally has a range of around
-1E+308 to +1E+308 with a precision of at least 15 digits. Values that
On most platforms, the <type>real</type> type has a range of at least
1E-37 to 1E+37 with a precision of at least 6 decimal digits. The
<type>double precision</type> type typically has a range of around
1E-307 to 1E+308 with a precision of at least 15 digits. Values that
are too large or too small will cause an error. Rounding may
take place if the precision of an input number is too high.
Numbers too close to zero that are not representable as distinct
from zero will cause an underflow error.
</para>
<para>
<productname>PostgreSQL</productname> also supports the SQL-standard
notations <type>float</type> and
<type>float(<replaceable>p</replaceable>)</type> for specifying
inexact numeric types. Here, <replaceable>p</replaceable> specifies
the minimum acceptable precision in binary digits.
<productname>PostgreSQL</productname> accepts
<type>float(1)</type> to <type>float(24)</type> as selecting the
<type>real</type> type, while
<type>float(25)</type> to <type>float(53)</type> select
<type>double precision</type>. Values of <replaceable>p</replaceable>
outside the allowed range draw an error.
<type>float</type> with no precision specified is taken to mean
<type>double precision</type>.
</para>
<note>
<para>
Prior to <productname>PostgreSQL</productname> 7.4, the precision in
<type>float(<replaceable>p</replaceable>)</type> was taken to mean
so many decimal digits. This has been corrected to match the SQL
standard, which specifies that the precision is measured in binary
digits. The assumption that <type>real</type> and
<type>double precision</type> have exactly 24 and 53 bits in the
mantissa respectively is correct for IEEE-standard floating point
implementations. On non-IEEE platforms it may be off a little, but
for simplicity the same ranges of <replaceable>p</replaceable> are used
on all platforms.
</para>
</note>
</sect2>
<sect2 id="datatype-serial">

3
doc/src/sgml/release.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.192 2003/05/28 16:03:55 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.193 2003/06/17 23:12:36 tgl Exp $
-->
<appendix id="release">
@ -24,6 +24,7 @@ CDATA means the content is "SGML-free", so you can write without
worries about funny characters.
-->
<literallayout><![CDATA[
Precision in FLOAT(p) is now interpreted as bits, not decimal digits
Functional indexes have been generalized into expressional indexes
CHAR(n) to TEXT conversion automatically strips trailing blanks
Pattern matching operations can use indexes regardless of locale