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To: Andrew Cagney <ac131313@redhat.com>
Cc: gdb-patches@sources.redhat.com
Subject: Re: Simulation of MIPS recip and rsqrt instructions
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	<3DE3D5BD.4070207@redhat.com>
From: Richard Sandiford <rsandifo@redhat.com>
Date: Tue, 26 Nov 2002 12:38:00 -0000
In-Reply-To: <3DE3D5BD.4070207@redhat.com>
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Andrew Cagney <ac131313@redhat.com> writes:
> Can this test case be written in strict assembler so that it can be
> added to the simulator testsuite?

Is there a testsuite for mips?

> > Unfortunately, sim_fpu_inv isn't commented and cp1.c seems to be
> > its only active user.  Which should change?
> 
> Hmm, I guess:
> 
> 	1 / (x * 2^y) == (1/x) * (1/(2^y)) == (1/x) * (2^(-y))
> 
> and
> 	1/x != x
> 
> so I think the inv() function should be fixed - that suggests it is
> pretty broken.

OK, so sim_fpu_inv() _is_ supposed to be a general reciprocal function?
Not just for powers of two, etc.?  It seemed so deliberate, it was
difficult to tell.

Like you say, there's probably some code that could be nicked
from elsewhere, but reusing sim_fpu_div should work too, even
if it isn't as efficient.  The patch below also fixes the
test case.

Richard


Index: sim/common/sim-fpu.c
===================================================================
RCS file: /cvs/src/src/sim/common/sim-fpu.c,v
retrieving revision 1.4
diff -c -d -p -F^[(a-zA-Z0-9_^#] -r1.4 sim-fpu.c
*** sim/common/sim-fpu.c	12 Jun 2002 00:46:11 -0000	1.4
--- sim/common/sim-fpu.c	26 Nov 2002 20:33:46 -0000
*************** INLINE_SIM_FPU (int)
*** 1754,1786 ****
  sim_fpu_inv (sim_fpu *f,
  	     const sim_fpu *r)
  {
!   if (sim_fpu_is_snan (r))
!     {
!       *f = *r;
!       f->class = sim_fpu_class_qnan;
!       return sim_fpu_status_invalid_snan;
!     }
!   if (sim_fpu_is_qnan (r))
!     {
!       *f = *r;
!       f->class = sim_fpu_class_qnan;
!       return 0;
!     }
!   if (sim_fpu_is_infinity (r))
!     {
!       *f = sim_fpu_zero;
!       f->sign = r->sign;
!       return 0;
!     }
!   if (sim_fpu_is_zero (r))
!     {
!       f->class = sim_fpu_class_infinity;
!       f->sign = r->sign;
!       return sim_fpu_status_invalid_div0;
!     }
!   *f = *r;
!   f->normal_exp = - r->normal_exp;
!   return 0;
  }
  
  
--- 1754,1760 ----
  sim_fpu_inv (sim_fpu *f,
  	     const sim_fpu *r)
  {
!   return sim_fpu_div (f, &sim_fpu_one, r);
  }