1*c9945492SAndroid Build Coastguard Worker #include "libm.h" 2*c9945492SAndroid Build Coastguard Worker 3*c9945492SAndroid Build Coastguard Worker /* k is such that k*ln2 has minimal relative error and x - kln2 > log(DBL_MIN) */ 4*c9945492SAndroid Build Coastguard Worker static const int k = 2043; 5*c9945492SAndroid Build Coastguard Worker static const double kln2 = 0x1.62066151add8bp+10; 6*c9945492SAndroid Build Coastguard Worker 7*c9945492SAndroid Build Coastguard Worker /* exp(x)/2 for x >= log(DBL_MAX), slightly better than 0.5*exp(x/2)*exp(x/2) */ __expo2(double x,double sign)8*c9945492SAndroid Build Coastguard Workerdouble __expo2(double x, double sign) 9*c9945492SAndroid Build Coastguard Worker { 10*c9945492SAndroid Build Coastguard Worker double scale; 11*c9945492SAndroid Build Coastguard Worker 12*c9945492SAndroid Build Coastguard Worker /* note that k is odd and scale*scale overflows */ 13*c9945492SAndroid Build Coastguard Worker INSERT_WORDS(scale, (uint32_t)(0x3ff + k/2) << 20, 0); 14*c9945492SAndroid Build Coastguard Worker /* exp(x - k ln2) * 2**(k-1) */ 15*c9945492SAndroid Build Coastguard Worker /* in directed rounding correct sign before rounding or overflow is important */ 16*c9945492SAndroid Build Coastguard Worker return exp(x - kln2) * (sign * scale) * scale; 17*c9945492SAndroid Build Coastguard Worker } 18