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From: jfc@athena.mit.edu (John F Carr)
Newsgroups: comp.sys.ibm.pc.rt
Subject: AOS floating point bug
Message-ID: <1990Sep17.061429.27757@athena.mit.edu>
Date: 17 Sep 90 06:14:29 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Distribution: na
Organization: Massachusetts Institute of Technology
Lines: 33


There is a bug in the floating point code generator for the 68881
(/usr/lib/libfp.a(f881gen.o)).  In some cases, single precision
floats in general registers can cause bad code generation (register
0 is marked as available for address calculations when it is [1]
not a valid base register for address calculations [2] in use).
Apparently hc doesn't generate much code that triggers this bug,
but gcc does.  This is a fix (it will be making its way though
official channels to IBM as well).


*** /source/bsd-4.3/rt/usr.lib/libfp/genfp/f881gen.c	Fri Jun 16 17:35:44 1989
--- f881gen.c	Mon Sep 17 01:53:39 1990
***************
*** 309,315 ****
  
  if (is_scratchg(gi, (rr & 0x0f)))
  	fp_free_genr(gi, (rr & 0x0f));
! if (is_scratchg(gi, (rr >> 4)))
  	fp_free_genr(gi, (rr >> 4));
  
  return (i);
--- 309,315 ----
  
  if (is_scratchg(gi, (rr & 0x0f)))
  	fp_free_genr(gi, (rr & 0x0f));
! if (is_double(rr) && is_scratchg(gi, (rr >> 4)))
  	fp_free_genr(gi, (rr >> 4));
  
  return (i);

--
    --John Carr (jfc@athena.mit.edu)