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From: sherm@poseidon.UUCP (Paul A. Sherman)
Newsgroups: net.micro.att
Subject: Re: 3b2/400 and floating point
Message-ID: <1394@poseidon.UUCP>
Date: Fri, 24-Jan-86 15:25:24 EST
Article-I.D.: poseidon.1394
Posted: Fri Jan 24 15:25:24 1986
Date-Received: Sat, 25-Jan-86 08:13:59 EST
References: <2403@gatech.CSNET> <1735@cuae2.UUCP>
Reply-To: sherm@poseidon.UUCP (60545457-Paul A. Sherman;LZ 3C-319;6316)
Organization: AT&T Information Systems, Lincroft NJ
Lines: 40
Summary: 

In article <1735@cuae2.UUCP> heiby@cuae2.UUCP (Heiby) writes:

>With the introduction of the MAU, there is a new version of the CCS available
>called Issue 3 (3.1 is current).  The "-f" option (if accepted at all) does
>nothing in this issue.  All floating point operations are executed by function
>calls (avoiding the trap overhead). 

The rest of Ron's article is quite accurate, but the Issue 3 (3.0 and 
3.1) CCS's DO accept and act upon the "-f" option for backward 
compatability reasons.  The "-f" flag works the same way as it has in 
previous releases of the CCS.  It causes a special version of the 
runtime startup routine (/lib/fcrt0.o instead of /lib/crt0.o) to be 
linked in.  This file sets up the traps that Ron discussed and causes 
the code in fptrap.o (from libc.a) to be included in the a.out.  

For programs compiled from scratch with Issue 3 this flag is indeed 
unnecessary and just causes larger code.  However, if you have any 
object modules (e.g.  archive libraries) that contain floating point 
and were built with previous releases of the CCS, linking them requires
the floating point trap.  Without it the (still illegal) floating point
opcodes contained within will cause a core dump at run time.  Building
with the "-f" flag to the Issue 3 CCS doesn't slow down floating point
operation on new code.  It still uses function calls for floating 
point operation and they use the MAU if it exists.  It does allow old 
binary modules to be linked in and perform (still high overhead) 
floating point operations.  

This flag becomes necessary if you are trying to link against vendor
distributed libraries that were built before Issue 3 of the CCS was
available.

By the way, Issue 4 of the CCS (for System V Release 3) continues this
same behaviour.  I haven't seen C-FP+ so I don't know whether it
allows this sort of backward compatability or not.
-- 

			Paul Sherman
			AT&T Information Systems, Lincroft, NJ
			{pegasus!phoenix}!poseidon!sherm
			(201) 576-6316