Update ENTERI() macro

[Steve Kargl]

On Tue, Mar 05, 2019 at 03:48:11PM +1100, Bruce Evans wrote:
> On Mon, 4 Mar 2019, Steve Kargl wrote:
> 
> > On Thu, Feb 28, 2019 at 07:15:14AM +1100, Bruce Evans wrote:
> >> ...
> >> I said to use your method of __typeof().  I tested this:
> >>
> >> XX --- /tmp/math_private.h	Sun Nov 27 17:58:57 2005
> >> XX +++ ./math_private.h	Thu Feb 28 06:17:26 2019
> >> XX @@ -474,21 +474,22 @@
> >> XX  /* Support switching the mode to FP_PE if necessary. */
> >> XX  #if defined(__i386__) && !defined(NO_FPSETPREC)
> >> XX -#define	ENTERI() ENTERIT(long double)
> >> XX -#define	ENTERIT(returntype)			\
> >> XX -	returntype __retval;			\
> >> XX +#define	ENTERI()				\
> >> XX  	fp_prec_t __oprec;			\
> >> XX  						\
> >> XX  	if ((__oprec = fpgetprec()) != FP_PE)	\
> >> XX  		fpsetprec(FP_PE)
> >> XX -#define	RETURNI(x) do {				\
> >> XX -	__retval = (x);				\
> >> XX -	if (__oprec != FP_PE)			\
> >> XX -		fpsetprec(__oprec);		\
> >> XX +#define	LEAVEI()				\
> >> XX +	if ((__oprec = fpgetprec()) != FP_PE)	\
> >> XX +		fpsetprec(FP_PE)
> >
> > Am I reading this diff wrong?  Should LEAVEI() be
> >
> > #define LEAVEI()			\
> > 	if (__oprec != FP_PE)		\
> > 		fpsetprec(__oprec)
> >
> > That is, we want to reset the precision to what ENTERI
> > grabbed in its conditinal expression.
> 
> Oops.  I wrote it wrong by copying the wrong clause.
> 
> The broken version even passed quick runtime tests.  This is because
> the tests know that most long double functions are missing ENTERI(),
> so they set the precision to FP_PE before the call.  So both ENTERI()
> and LEAVEI() find (__oprec = fpgetprec() equal to FP_PE and do nothing.
> 

My math_private.h has a few additions, which meant I applied
your diff manually.  As I was reading it, I came across the
issue.

I think I have the s_cexpl.c file fixed to use LDBL_EXTRACT_WORDS
instead of the new macro I introduced.  I however cannot figure
out what David Das did to arrive at k_exp.c, so I cannot write
a similar k_cexpl.c.  Yes, I added the 'c' in the name to avoid
confusion in ld80/.  In particular, I have no idea how he found
his scaling value 'k'.  Any insights?

-- 
Steve