vendor/libm/src/math/k_expo2f.rs

   1 use super::expf;
   2
   3 /* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */
   4 const K: i32 = 235;
   5
   6 /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */
   7 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
   8 pub(crate) fn k_expo2f(x: f32) -> f32 {
   9     let k_ln2 = f32::from_bits(0x4322e3bc);
  10     /* note that k is odd and scale*scale overflows */
  11     let scale = f32::from_bits(((0x7f + K / 2) as u32) << 23);
  12     /* exp(x - k ln2) * 2**(k-1) */
  13     expf(x - k_ln2) * scale * scale
  14 }