1 #include "libm.h" 2 3 /* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */ 4 static const int k = 235; 5 static const float kln2 = 0x1.45c778p+7f; 6 7 /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */ 8 float __expo2f(float x) 9 { 10 float scale; 11 12 /* note that k is odd and scale*scale overflows */ 13 SET_FLOAT_WORD(scale, (uint32_t)(0x7f + k/2) << 23); 14 /* exp(x - k ln2) * 2**(k-1) */ 15 return expf(x - kln2) * scale * scale; 16 } 17