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From: Ken Garlington <garlingtonke@lmtas.lmco.com>
Subject: Re: 'Digit in generic package
Date: 1996/08/27
Message-ID: <32231881.2A09@lmtas.lmco.com>#1/1
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references: <9608261530.AA06035@most>
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organization: Lockheed Martin Tactical Aircraft Systems
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Date: 1996-08-27T00:00:00+00:00
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W. Wesley Groleau (Wes) wrote:
> 
> R. A. O'Keefe asked
> [how to make a generic use the most precise type out of its actuals]
> 
> R. Eachus answered
> 
>   [Write the generic body to dispatch at run-time]
> 
> At least one vendor supplied a generic math package that did exactly
> that AND on examining the disassembled code for an instantiation, we
> found that the compiler had looked at the parameters and eliminated
> the "dead code" so that the effect was exactly what Mr. O'Keefe had
> asked for.

If you have DEC Ada installed, you can look at the body of the generic 
SQRT routine in ADA$PREDEFINED:MATH_LIB.ADC and see:

function SQRT (A: REAL) return REAL is
begin
  if REAL'MACHINE_MANTISSA = SYSTEM.F_FLOAT'MACHINE_MANTISSA then
    return REAL(VAX_F.SQRT(F_FLOAT(A)));
  elsif REAL'MACHINE_MANTISSA = SYSTEM.D_FLOAT'MACHINE_MANTISSA then
    ...

Usually, this gets optimized to a simple call to the pre-defined VAX
SQRT routine of the appropriate precision.

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