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G.2.2 Model-Oriented Attributes of Floating Point Types
In implementations that support the Numerics Annex, the model-oriented
attributes of floating point types shall yield the values defined here, in both the strict and the relaxed modes. These definitions add conditions to
those in A.5.3.
Static Semantics
For every subtype S of a floating point type T:
S'Model_Mantissa
Yields the number of digits in the mantissa of the canonical
form of the model numbers of T (see A.5.3). The value of
this attribute shall be greater than or equal to
Ceiling(d*log (10)/log (T'Machine_Radix))+1, where d is the
requested decimal precision of T. In addition, it shall be
less than or equal to the value of T'Machine_Mantissa. This
attribute yields a value of the type universal_integer.
S'Model_Emin
Yields the minimum exponent of the canonical form of the
model numbers of T (see A.5.3). The value of this attribute
shall be greater than or equal to the value of T'Machine_Emin. This attribute yields a value of the type universal_integer.
S'Safe_First
Yields the lower bound of the safe range of T. The value of
this attribute shall be a model number of T and greater than
or equal to the lower bound of the base range of T. In addition, if T is declared by a floating_point_definition or
is derived from such a type, and the floating_point_definition includes a real_range_specification specifying a
lower bound of lb, then the value of this attribute shall be
less than or equal to lb; otherwise, it shall be less than or
equal to -10.0**(4*d), where d is the requested decimal precision
of T. This attribute yields a value of the type universal_real.
S'Safe_Last
Yields the upper bound of the safe range of T. The value of
this attribute shall be a model number of T and less than or
equal to the upper bound of the base range of T. In addition, if T is declared by a floating_point_definition or
is derived from such a type, and the floating_point_definition includes a real_range_specification specifying an
upper bound of ub, then the value of this attribute shall be
greater than or equal to ub; otherwise, it shall be greater
than or equal to 10.0**(4*d), where d is the requested decimal
precision of T. This attribute yields a value of the type
universal_real.
S'Model
Denotes a function (of a parameter X) whose specification is
given in A.5.3. If X is a model number of T, the function
yields X; otherwise, it yields the value obtained by rounding
or truncating X to either one of the adjacent model numbers
of T. Constraint_Error is raised if the resulting model
number is outside the safe range of S. A zero result has the
sign of X when S'Signed_Zeros is True.
Subject to the constraints given above, the values of S'Model_Mantissa
and S'Safe_Last are to be maximized, and the values of S'Model_Emin and
S'Safe_First minimized, by the implementation as follows:
- First, S'Model_Mantissa is set to the largest value for which
values of S'Model_Emin, S'Safe_First, and S'Safe_Last can be
chosen so that the implementation satisfies the strict-mode
requirements of G.2.1 in terms of the model numbers and safe
range induced by these attributes.
- Next, S'Model_Emin is set to the smallest value for which values
of S'Safe_First and S'Safe_Last can be chosen so that the
implementation satisfies the strict-mode requirements of G.2.1 in terms of the model numbers and safe range induced by these
attributes and the previously determined value of S'Model_Mantissa.
- Finally, S'Safe_First and S'Safe_last are set (in either order)
to the smallest and largest values, respectively, for which the
implementation satisfies the strict-mode requirements of G.2.1 in terms of the model numbers and safe range induced by these
attributes and the previously determined values of S'Model_Mantissa and S'Model_Emin.
About DocAda Light:
Preface / Preliminary
/ Help
/ TOC
/ Copyright
DocAda Online at the Ada Home:
Complete RM95
/ Updates
/ News
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