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From: macrakis@harvard.ARPA (Stavros Macrakis)
Newsgroups: net.lang,net.lang.ada
Subject: Re: What language do you use for scientific programming?
Message-ID: <324@harvard.ARPA>
Date: Tue, 27-Aug-85 13:11:24 EDT
Article-I.D.: harvard.324
Posted: Tue Aug 27 13:11:24 1985
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Organization: Aiken Comp. Lab., Harvard
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> >[Ada] does have double-precision real.... you can ... specify
> >arbitrary precision, [but if there's no appropriate] hardware data
> >type,... you could be executing... simulation code).
> 
> No simulation code is ever required.  Ada allows operations to be
> performed with more precision than the user requested.  Therefore,
> all operations are done with the next better floating point type in
> the machine.  The "predefined types" of the implementation should
> correspond with supported types on the machine.

These two notes appear to be talking to to different issues: run-time
calculations in floating types, and calculation of `universal numbers'
at compile time.

Ada allows <specification> of the precision of floating types.  An
implementation chooses which precisions it supports, and must give an
error if a program specifies a precision it does not support.
Implementations are required to support at least one floating
precision.  Precisions are specifed by number of digits rather than
as `single' or `double' precision, increasing portability.

As for compile-time constants (`universal numbers'): "The accuracy of
the evaluation of [such numbers] is at least as good as that of the
most accurate predefined floating point type...." [Ada RM 4.10/4]
Earlier versions of Ada did apparently require arbitrary-precision
arithmetic at compile time (but never at run time).

Of course, if you want run-time multiple precision, you are free to
implement it in a package and use overloading to call its operations
`+', `*', etc.  This holds true for vector-matrix, complex, and other
types as well.

> All in all, I agree with you in selecting Ada as your language of
> choice.  Unlike C, however, an efficient Ada program requires a
> damn-good optimizing compiler.	-- Joe Orost

I also agree.  Choose Ada for numeric calculations.  This year's crop
of compilers finally seems to be fulfilling Ada's promise.

	-s