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On Tue, 21 May 2024 05:49:55 -0000 (UTC)
Thomas Koenig <tkoenig@netcologne.de> wrote:
>BGB <cr88192@gmail.com> schrieb:>
Granted, they are not necessarily the option one would go if they
wanted "cheapest possible FPU that is still good enough to be
usable".
>
Though, the point at which an FPU manages to suck badly enough that
one needs to resort to software emulation to make software work, is
probably a lower limit.
>
>
Luckily, "uses 754 formats, but with aggressive cost cutting" can
be "good enough", and so long as they more-or-less deliver a full
width mantissa, and can exactly compute exact-value calculations,
most software is generally going to work.
This will require extensive testing and possibly modification for
a lot of software ported to such a system. This will drive up
the total cost, presumably far more than any hardware savings.
But OTOH, if 1.0+2.0 gives 2.999999, that is, not good enough, so
there is a lower limit here.
An example of a more interesting question is
if (a >= 0.) {
if (b >= 0) {
if (a + b < a) {
printf("We should never get here!\n);
abort();
}
}
}
If I am not mistaken, that should hold on VAX, which has floating-point
very close to BGB ideal. It looks like it would hold even on less
robust formats, like IBM's hex float. I wonder where it is not true?
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