Why do you need a 387 to run X11R3?

[Clayton Haapala]

In article <20301 at nuchat.UUCP> steve at nuchat.UUCP (Steve Nuchia) writes:
>Dynamic linking is about the only good solution, but you still have
>to allow the heavy FP users to compile for specific hardware to
>avoid the two jumps per FLOP overhead.  There was a scheme proposed
>in which illegal instructions were compiled into the program and
>replaced at run time with the "right" intruction by the kernel.  Don't
>know if that ever went out with a commercial system.

I think XENIX uses a variation of that scheme -- an initial fault on the
first time an FP instruction is attempted, then the kernel "hot patches"
the binary with a transfer to the right emulation code.  Next time through
there is no fault, just a call.  Has to be faster than a complete context
switch with a fault, I would think.

I heard this rumor when I was working with XENIX 3 for 286 boxes.  I know
from empirical evidence that XENIX FPP emulation beats the pants off of
SysV 386 emulation.

Say, anybody try the IIT 3C87?  It's a clone of the Intel 80387, supposed to
run 25-30% faster.  They also have a 287 replacement.  I'm thinking of buying
one in a couple of weeks unless I hear terrible things about its performance
under XENIX/UNIX.
-- 
Clayton Haapala                ...!bungia!uci!clay (clay at uci.uci.com)
Unified Communications Inc.    "Every morning I get in the Queue.
3001 Metro Drive - Suite 500    'n get on the Bus that takes me to you."
Bloomington, MN  55425             -- the Who