General Bug Report: Incorrect subtraction - rounding error - should NOT round!

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Jeffrey Springer
Your email address : jspringr(at)savemail(dot)com

Category : runtime: back-end: SQL
Severity : critical

Summary: Incorrect subtraction - rounding error - should NOT round!

System Configuration
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Operating System : FreeBSD 2.2.7

PostgreSQL version : 6.3.2

Compiler used : gcc 2.7

Hardware:
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AMD K6 with 32M Ram

Versions of other tools:
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gmake

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Problem Description:
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I put together a banking web-site using Postgres. I put a
check and deducted the amount from the balance column of
the bank_account table. The result was incorrect so I tested
it inside psql instead of my C++ program but got the
same result.

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Test Case:
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template1=> select 166952.9 - 166384.34 ;
?column?
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568.559999999998
(1 row)

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Solution:
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