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Path: utzoo!attcan!uunet!ibmpa!slo!jsalter
From: jsalter@slo.uucp (James Salter)
Newsgroups: comp.unix.i386,comp.unix.xenix,comp.unix.wizards
Subject: Re: floating point exception status not inherited by exec
Message-ID: <4624@ibmpa.UUCP>
Date: 25 Mar 90 03:29:38 GMT
References: <795@s7.Morgan.COM>
Sender: news@ibmpa.UUCP
Reply-To: jsalter@slo.UUCP (James Salter)
Organization: IBM AWD, Palo Alto
Lines: 36

In article <795@s7.Morgan.COM> amull@Morgan.COM (Andrew P. Mullhaupt) writes:
>
>	On SCO UNIX System V/386 R3.2:
>
>I need to preserve the state of the floating point exception mask
>across an exec(). Experiments show that the exception mask and the
>sticky bit status seems to be preserved across fork() (i.e. is
>inherited by a child) but when exec is invoked, the exceptions may
>change. This has ummm - 'unpleasant' consequences. Note that it
>is not sufficient to work at the level of SIGFPE, but it is actually
>required to specify the floating point exception mask and sticky bit
>status to different values than the (otherwise sensible) defaults.

You mean apart from rewriting the exec() function?  :-)

Realistically, the only way you could preserve the state is through a
save mechanism before the exec() and a restore after the exec().

In the System V/386 3.2 programmer's reference manual I have, it lists
some routines under FPGETROUND(3C).  Including the functions:
	fpgetmask(), fpsetmask(), fpgetsticky(), fpsetsticky()
and the include file:
	#include <ieeefp.h>

I don't know what SCO version does...

To do your own such routines, it would require some machine coding and
use of at least a short int to save just the status word.  If you require
the status AND the control word to be saved, just store it into a long int
and do some byte shifting.  Or use two shorts if you're lazy...

>Andrew Mullhaupt

jim/jsalter   IBM AWD   T465/(415)855-4427    VNET: JSALTER at PALOALTO
UUCP: ..!uunet!ibmsupt!jsalter               Disc: Any opinions are mine.
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