the problem and solution are discussed here
	http://9fans.net/archive/2009/01/234
since the post, i removed the underflow test as i found
it was not effective, at least on the 386.  you may disagree.

further note: there is also lib/ap/gen/strtod.c which
seems to suffer from many overflow/underflow problems.
i didn't change it because i don't understand why another
copy of strtod is necessary.

Reference: /n/sources/patch/applied/apestrtod
Date: Thu Jul 30 15:13:44 CES 2009
Signed-off-by: quanstro@quanstro.net

--- /sys/src/ape/lib/ap/stdio/strtod.c	Thu Jul 30 15:11:25 2009
+++ /sys/src/ape/lib/ap/stdio/strtod.c	Thu Jul 30 15:11:23 2009
@@ -394,6 +394,8 @@
 	/* Get starting approximation = rv * 10**e1 */
 
 	if (e1 > 0) {
+		if(nd0 + e1 - 1> DBL_MAX_10_EXP)
+			goto ovfl;
 		if (i = e1 & 15)
 			rv.d *= tens[i];
 		if (e1 &= ~15) {