Update ENTERI() macro

[Bruce Evans]

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.

Bruce