static const double kln2 = 0x1.62066151add8bp+10;
/* exp(x)/2 for x >= log(DBL_MAX), slightly better than 0.5*exp(x/2)*exp(x/2) */
-double __expo2(double x)
+double __expo2(double x, double sign)
{
double scale;
/* note that k is odd and scale*scale overflows */
INSERT_WORDS(scale, (uint32_t)(0x3ff + k/2) << 20, 0);
/* exp(x - k ln2) * 2**(k-1) */
- return exp(x - kln2) * scale * scale;
+ /* in directed rounding correct sign before rounding or overflow is important */
+ return exp(x - kln2) * (sign * scale) * scale;
}