1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
fn prior_power_of_two(x: usize) -> usize {
((x as u128).next_power_of_two() >> 1) as usize
}
pub fn const_sort<T, F>(v: &mut [T], cmp: &F)
where
F: Fn(&T, &T) -> subtle::Choice,
T: subtle::ConditionallySwappable,
{
let t = prior_power_of_two(v.len());
let mut p = t;
while p > 0 {
let mut q = t;
let mut r = 0;
let mut d = p;
while d > 0 {
for i in 0..(v.len()-d) {
if (i & p) == r {
let (f,l) = v.split_at_mut(1+i);
compare_and_swap(&mut l[d-1], &mut f[i], cmp);
}
}
d = q -p;
q >>=1;
r = p;
}
p >>=1;
}
}
#[inline(always)]
fn compare_and_swap<T, F>(v: &mut T, s: &mut T, cmp: &F)
where
F: Fn(&T, &T) -> subtle::Choice,
T: subtle::ConditionallySwappable,
{
let choice: subtle::Choice = cmp(&v, &s);
v.conditional_swap(s, choice);
}
#[cfg(test)]
mod tests {
use rand::prelude::*;
#[test]
fn test_correct() {
for x in 0..=255usize {
let mut a = vec![0; x];
for val in a.iter_mut() {
*val = thread_rng().gen_range(0, 100);
}
crate::const_sort(&mut a, &|l, r| ((l < r) as u8).into());
let mut ans = a.clone();
ans.sort();
assert_eq!(ans, a);
}
}
#[test]
fn test_bitonic_u8_exhaustive() {
for x in 0..=7u8 {
let mut a = [1u8 & (x >> 0), 1u8 & (x >> 1), 1u8 & (x >> 2)];
crate::const_sort(&mut a, &|l, r| ((l < r) as u8).into());
let mut ans = a.clone();
ans.sort();
assert_eq!(ans, a);
}
}
#[test]
fn test_bitonic_random_large_prime() {
for _ in 0..=255u8 {
let mut a = [0u8; 7919];
for i in 0..7919 {
a[i] = thread_rng().gen_range(0, 1);
}
crate::const_sort(&mut a, &|l, r| ((l < r) as u8).into());
let mut ans = a.clone();
ans.sort();
assert_eq!(ans[..], a[..]);
}
}
}