From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeffrey A Law <law@redhat.com>
To: "John David Anglin" <dave@hiauly1.hia.nrc.ca>
Cc: meissner@cygnus.com (Michael Meissner), gcc-patches@gcc.gnu.org
Subject: Re: PATCH: HUGE_VAL should be Infinity 
Date: Mon, 04 Dec 2000 11:35:00 -0000
Message-id: <8886.975958640@upchuck>
References: <200012041925.OAA06848@hiauly1.hia.nrc.ca>
X-SW-Source: 2000-12/msg00183.html

  In message < 200012041925.OAA06848@hiauly1.hia.nrc.ca >you write:
  > I am planning to implement ieee compatible negdf2 and negsf2 insns for
  > PA1.X machines.  It looked like multiplaction by -1 would be the most
  > efficient implementation since twiddling the sign bit of a floating
  > pointer register appears to involve copying to a general register via
  > memory and back again.  Multiplaction also looks simpler.  If Jeff can
  > recall whether or not there are corner effects with the multiplication
  > method it would be useful.
Found it.  fneg is non-arithmetic and does not cause an invalid operation
exception when a NaN is negated.

fmul is arithmetic and will cause exceptions.  Basically using any kind
of arithmetic insn to implement fneg loses in some form or another.


jeff