3 /* k is such that k*ln2 has minimal relative error and x - kln2 > log(DBL_MIN) */
4 static const int k
= 2043;
5 static const double kln2
= 0x1.62066151add8bp
+10;
7 /* exp(x)/2 for x >= log(DBL_MAX), slightly better than 0.5*exp(x/2)*exp(x/2) */
8 double __expo2(double x
)
12 /* note that k is odd and scale*scale overflows */
13 INSERT_WORDS(scale
, (uint32_t)(0x3ff + k
/2) << 20, 0);
14 /* exp(x - k ln2) * 2**(k-1) */
15 return exp(x
- kln2
) * scale
* scale
;