IEEE 60559-2011 pdf free download – Information technology – Microprocessor Systems – Floating-Point arithmetic.
4. Attributes and rounding
4.1 Attribute specification An attribute is logically associated with a program block to modify its numerical and exception semantics. A user can specify a constant value for an attribute parameter. Some attributes have the effect of an implicit parameter to most individual operations of this standard; language standards shall specify ― rounding-direction attributes (see 4.3) and should specify
― alternate exception handling attributes (see 8). Other attributes change the mapping of language expressions into operations of this standard; language standards that permit more than one such mapping should provide support for:
― preferredWidth attributes (see 10.3)
― value-changing optimization attributes (see 10.4)
― reproducibility attributes (see 11). For attribute specification, the implementation shall provide language-defined means, such as compiler directives, to specify a constant value for the attribute parameter for all standard operations in a block; the scope of the attribute value is the block with which it is associated. Language standards shall provide for constant specification of the default and each specific value of the attribute.
4.2 Dynamic modes for attributes Attributes in this standard shall be supported with the constant specification of 4.1.
Particularly to support debugging, language standards should also support dynamic-mode specification of attributes. With dynamic-mode specification, a user can specify that the attribute parameter assumes the value of a dynamic-mode variable whose value might not be known until program execution. This standard does not specify the underlying implementation mechanisms for constant attributes or dynamic modes. For dynamic-mode specification, the implementation shall provide language-defined means to specify that the attribute parameter assumes the value of a dynamic-mode variable for all standard operations within the scope of the dynamic-mode specification in a block.
The implementation initializes a dynamic-mode variable to the default value for the dynamic mode. Within its language-defined (dynamic) scope, changes to the value of a dynamic-mode variable are under the control of the user via the operations in 9.3.1 and . The following aspects of dynamic-mode variables are language-defined; language standards may explicitly defer the definitions to implementations:
― The precedence of static attribute specifications and dynamic-mode assignments.
― The effect of changing the value of the dynamic-mode variable in an asynchronous event, such as in another thread or signal handler.
― Whether the value of the dynamic-mode variable can be determined by non-programmatic means, such as a debugger.
NOTE — A constant value for an attribute can be specified and meet the requirements of 4.1 by a dynamic mode specification with appropriate scope of that constant value.IEEE 60559 pdf download.