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Commit | Line | Data |
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cdc7bbd5 XL |
1 | use super::exp; |
2 | ||
3 | /* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */ | |
4 | const K: i32 = 2043; | |
5 | ||
6 | /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */ | |
cdc7bbd5 XL |
7 | #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
8 | pub(crate) fn k_expo2(x: f64) -> f64 { | |
9 | let k_ln2 = f64::from_bits(0x40962066151add8b); | |
10 | /* note that k is odd and scale*scale overflows */ | |
11 | let scale = f64::from_bits(((((0x3ff + K / 2) as u32) << 20) as u64) << 32); | |
12 | /* exp(x - k ln2) * 2**(k-1) */ | |
13 | exp(x - k_ln2) * scale * scale | |
14 | } |