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Re: [avr-gcc-list] linear regression on 128L

From: Daniel O'Connor
Subject: Re: [avr-gcc-list] linear regression on 128L
Date: Tue, 5 Apr 2005 22:14:39 +0930
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On Tue, 5 Apr 2005 19:46, Joerg Wunsch wrote:
> "Daniel O'Connor" <address@hidden> wrote:
> > Surely if double =3D=3D 4 bytes and float =3D=3D 4 bytes then double
> > is wor= thless...
> Many people obviously don't find it worthless. ;-)


> The point is, C basically depends on ``floating point support'' being
> ``type double supported''.  If all you have is a 32-bit FP library,
> you can then decide whether you don't want to offer *any* FP support,
> or whether you ship with 32-bit FP being declared as `double'.

Fair enough..
#define double float

> > Is there some hidden cost for double =3D=3D 8 that doesn't affect
> > people us= ing=20 doubles?
> Yes, C assumes on all ends that the default FP type is double.  FP
> expressions promote to it, much the same way integer expressions
> promote to `int' (which has already caused the infamous invention of
> the -mint8 compiler option).  *Many* people wouldn't want to pay for
> the bloat.
> Also, remember that a 64-bit FP library for the AVR is still
> vapourware (at least one in a form that could be integrated smoothely
> with the compiler).  *Once* we *might* have it, but then, the
> installed base which assumes 32-bit doubles has to be considered as
> historical baggage to care for.

OK, I didn't realise double was such a mandatory part of it :(

Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C

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