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Auto merge of #107638 - zhangyunhao116:pdqsort-rand, r=cuviper

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Optimize break patterns

Use `wyrand` instead of calling `XORSHIFT` 2 times in break patterns for the 64-bit platform. The new PRNG is 2x faster than the previous one.

Bench result(via https://gist.github.com/zhangyunhao116/11ef41a150f5c23bb47d86255fbeba89):
```
old                     time:   [1.3258 ns 1.3262 ns 1.3266 ns]
                        change: [+0.5901% +0.6731% +0.7791%] (p = 0.00 < 0.05)
                        Change within noise threshold.
Found 13 outliers among 100 measurements (13.00%)
  7 (7.00%) high mild
  6 (6.00%) high severe

new                     time:   [657.65 ps 657.89 ps 658.18 ps]
                        change: [-1.6910% -1.6110% -1.5256%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  2 (2.00%) high mild
  4 (4.00%) high severe
```
This commit is contained in:
bors 2023-02-25 03:01:40 +00:00
commit 6ffabf3c8f
1 changed files with 14 additions and 10 deletions
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24
library/core/src/slice/sort.rs
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@ -673,19 +673,23 @@ where
fn break_patterns<T>(v: &mut [T]) {
let len = v.len();
if len >= 8 {
// Pseudorandom number generator from the "Xorshift RNGs" paper by George Marsaglia.
let mut random = len as u32;
let mut gen_u32 = || {
random ^= random << 13;
random ^= random >> 17;
random ^= random << 5;
random
};
let mut seed = len;
let mut gen_usize = || {
// Pseudorandom number generator from the "Xorshift RNGs" paper by George Marsaglia.
if usize::BITS <= 32 {
gen_u32() as usize
let mut r = seed as u32;
r ^= r << 13;
r ^= r >> 17;
r ^= r << 5;
seed = r as usize;
seed
} else {
(((gen_u32() as u64) << 32) | (gen_u32() as u64)) as usize
let mut r = seed as u64;
r ^= r << 13;
r ^= r >> 7;
r ^= r << 17;
seed = r as usize;
seed
}
};