Re: Float numbers in module programming
From: Phillip Susi
Date: Thu Mar 30 2006 - 12:20:45 EST
linux-os (Dick Johnson) wrote:
No. Any file I/O, or anything that takes time sleeps and gives up
the CPU, ultimately calling schedule(). That means that anybody
can have its coprocessor state dorked. This has been discussed many
The FPU state is saved across normal thread switches if either the new
or old thread uses the fpu, so this should be safe. Unless this does
not apply to kernel threads?
times. Also, floating-point is never required for anything!!! It's
just a convenience for people who like to write code using 10 fingers.
It has real problems when trying to exactly represent real numbers.
For instance __all__ real numbers, except for transcendentals, can
be represented as a ratio of two integers. For instance, you can't
represent 1/3 exactly as a decimal. It is, however exactly the ratio
of 1 and 3, two integers. Given this, I'm sure you can find a way
to perform high-precision mathematics within the kernel without
using the coprocessor. Usually, it's just a little thought that
is required. Somebody needs 8 bits to feed into a volume-control
register, but the value needs to be log-scale. Trivial, even if
you don't want to use a table.
Agreed, adjusting your thinking a bit to stick to integer math is
usually preferred for efficiency reasons.
If you divulge the mathematics you need calculated, I'll bet you
will get many answers from responders to the linux-kernel list.
However, if you expect to use the coprocessor as part of an image
processing routine and your driver was designed to use that
coprocessor, then you need a private coprocessor or you need
a user-space 'driver' that probably communicates using shared-
memory, this not involving kernel code at all.
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