(2nd time) tweaks to erff() threshold values

[Bruce Evans]

On Fri, 23 Aug 2013, Steve Kargl wrote:

> On Fri, Aug 23, 2013 at 09:12:33PM +1000, Bruce Evans wrote:
>>
>> @ 	if(ix < 0x3f580000) {		/* |x|<0.84375 */
>> @ 	    if(ix < 0x38800000) { 	/* |x|<2**-14 */
>> @ 	        if (ix < 0x04000000)	/* |x|<0x1p-119 */
>> @ 		    return (8*x+efx8*x)/8;  /*avoid spurious underflow */
>
> To keep the diff between s_erf.c and s_erff.c small, do you
> want my to update s_erf.c with the last line above?

Yes, including the style change from *0.125 to /8 and any similar style
changes you can find (or don't change this anywhere), and the comment
on the threshold for underflow.

Bruce