DECFLOAT underflow should yield zero instead of an error
--------------------------------------------------------
Key: CORE-5700
URL: http://tracker.firebirdsql.org/browse/CORE-5700
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 4.0 Alpha 1
Reporter: Mark Rotteveel
A DECFLOAT underflow (that is if the exponent is smaller than the minimum
supported exponent), currently yields an error. However, based on the rules in
SQL:2016 5.3 <literal> and 6.13 <cast specification>, this should instead yield
0 (either really 0E0, or maybe 0E<lowest valid exponent>).
Specifically from 5.3 (full quote below): ""Underflow", i.e., specifying a
nonzero value so close to 0 (zero) that the closest representation in the
SQL-implementation's internal representation is 0E0, is a special case of the
latter condition, and is not a syntax error"
====
*** IBPP::SQLException ***
Context: Statement::Fetch
Message: isc_dsql_fetch failed.
SQL Message : -901
Unsuccessful execution caused by system error that does not preclude successful
execution of subsequent statements
Engine Code : 335545143
Engine Message :
Decimal float underflow. The exponent of a result is less than the magnitude
allowed.
====
"""
23) It is implementation-defined whether the declared type of an <approximate
numeric literal> ANL is an implementation-defined approximate numeric type or
the decimal floating-point type with an implementation-defined precision. If
the declared type of ANL is an approximate numeric type, then the value of ANL
shall not be greater than the maximum value nor less than the minimum value
that can be represented by the approximate numeric types. If the declared type
of ANL is the decimal floating-point type, then the value of ANL shall not be
greater than the maximum value nor less than the minimum value that can be
represented by the decimal floating-point type.
NOTE 142 — Thus the only syntax error for an <approximate numeric literal> is
what is commonly known as "overflow"; there is no syntax error for specifying
more significant digits than the SQL-implementation can represent internally,
nor for specifying a value that has no exact equivalent in the
SQL-implementation's internal representation. ("Underflow", i.e., specifying a
nonzero value so close to 0 (zero) that the closest representation in the
SQL-implementation's internal representation is 0E0, is a special case of the
latter condition, and is not a syntax error.)
"""
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