1 | #[cfg_attr (all(test, assert_no_panic), no_panic::no_panic)] |
2 | pub fn scalbn(x: f64, mut n: i32) -> f64 { |
3 | let x1p1023 = f64::from_bits(0x7fe0000000000000); // 0x1p1023 === 2 ^ 1023 |
4 | let x1p53 = f64::from_bits(0x4340000000000000); // 0x1p53 === 2 ^ 53 |
5 | let x1p_1022 = f64::from_bits(0x0010000000000000); // 0x1p-1022 === 2 ^ (-1022) |
6 | |
7 | let mut y = x; |
8 | |
9 | if n > 1023 { |
10 | y *= x1p1023; |
11 | n -= 1023; |
12 | if n > 1023 { |
13 | y *= x1p1023; |
14 | n -= 1023; |
15 | if n > 1023 { |
16 | n = 1023; |
17 | } |
18 | } |
19 | } else if n < -1022 { |
20 | /* make sure final n < -53 to avoid double |
21 | rounding in the subnormal range */ |
22 | y *= x1p_1022 * x1p53; |
23 | n += 1022 - 53; |
24 | if n < -1022 { |
25 | y *= x1p_1022 * x1p53; |
26 | n += 1022 - 53; |
27 | if n < -1022 { |
28 | n = -1022; |
29 | } |
30 | } |
31 | } |
32 | y * f64::from_bits(((0x3ff + n) as u64) << 52) |
33 | } |
34 | |