libm/math/
nextafter.rs

1#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
2pub fn nextafter(x: f64, y: f64) -> f64 {
3    if x.is_nan() || y.is_nan() {
4        return x + y;
5    }
6
7    let mut ux_i = x.to_bits();
8    let uy_i = y.to_bits();
9    if ux_i == uy_i {
10        return y;
11    }
12
13    let ax = ux_i & !1_u64 / 2;
14    let ay = uy_i & !1_u64 / 2;
15    if ax == 0 {
16        if ay == 0 {
17            return y;
18        }
19        ux_i = (uy_i & 1_u64 << 63) | 1;
20    } else if ax > ay || ((ux_i ^ uy_i) & 1_u64 << 63) != 0 {
21        ux_i -= 1;
22    } else {
23        ux_i += 1;
24    }
25
26    let e = ux_i >> 52 & 0x7ff;
27    // raise overflow if ux.f is infinite and x is finite
28    if e == 0x7ff {
29        force_eval!(x + x);
30    }
31    let ux_f = f64::from_bits(ux_i);
32    // raise underflow if ux.f is subnormal or zero
33    if e == 0 {
34        force_eval!(x * x + ux_f * ux_f);
35    }
36    ux_f
37}