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(FLT_MIN) */ 4*c9945492SAndroid Build Coastguard Worker static const int k = 235; 5*c9945492SAndroid Build Coastguard Worker static const float kln2 = 0x1.45c778p+7f; 6*c9945492SAndroid Build Coastguard Worker 7*c9945492SAndroid Build Coastguard Worker /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */ __expo2f(float x,float sign)8*c9945492SAndroid Build Coastguard Workerfloat __expo2f(float x, float sign) 9*c9945492SAndroid Build Coastguard Worker { 10*c9945492SAndroid Build Coastguard Worker float 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 SET_FLOAT_WORD(scale, (uint32_t)(0x7f + k/2) << 23); 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 expf(x - kln2) * (sign * scale) * scale; 17*c9945492SAndroid Build Coastguard Worker } 18