TDF Specification, Issue 4.0

January 1998

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4.1 - Definition of terms
4.2 - Properties of Installers

4. Installer Behaviour

4.1. Definition of terms

In this document the behaviour of TDF installers is described in a precise manner. Certain words are used with very specific meanings. These are:

4.2. Properties of Installers

All installers must implement all of the constructions of TDF. There are some constructions where the installers may impose limits on the ranges of values which are implemented. In these cases the description of the installer must specify these limits.

Installers are not expected to check that the TDF they are processing is well-formed, nor that undefined constructs are absent. If the TDF is not well-formed any effect is permitted.

Installers shall only implement optimisations which are correct in all circumstances. This correctness can only be shown by demonstrating the equivalence of the transformed program, from equivalences deducible from this specification or from the ordinary laws of arithmetic. No statements are made in this specification of the form "such and such an optimisation is permitted".

Fortran90 has a notion of mathematical equivalence which is not the same as TDF equivalence. It can be applied to transform programs provided parentheses in the text are not crossed. TDF does not acknowledge this concept. Such transformations would have to be applied in a context where the permitted changes are known.

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