| use super::exp; |
| |
| /* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */ |
| const K: i32 = 2043; |
| |
| /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */ |
| #[inline] |
| #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
| pub(crate) fn k_expo2(x: f64) -> f64 { |
| let k_ln2 = f64::from_bits(0x40962066151add8b); |
| /* note that k is odd and scale*scale overflows */ |
| let scale = f64::from_bits(((((0x3ff + K / 2) as u32) << 20) as u64) << 32); |
| /* exp(x - k ln2) * 2**(k-1) */ |
| exp(x - k_ln2) * scale * scale |
| } |
