Sierpinski triangle generator

.gitignore

/target

README.md

cargo bench

n	time
1	33 ns
2	53 ns
3	150 ns
4	315 ns
5	803 ns
6	3674 ns

benches.rs

use criterion::{black_box, Criterion, criterion_group, criterion_main};

use std::ptr;

#[derive(Default, Copy, Clone, Debug)]
struct Pos {
    x: f64,
    y: f64,
}

impl Pos {
    fn mid(self, other: Pos) -> Pos {
        Pos {
            x: (self.x + other.x) / 2.0,
            y: (self.y + other.y) / 2.0,
        }
    }
}

#[derive(Default, Copy, Clone, Debug)]
struct Triangle {
    a: Pos,
    b: Pos,
    c: Pos,
}

fn bench_sierpinski(c: &mut Criterion) {
    c.bench_function("sierpinski", |b| {
        b.iter(|| {
            let n = black_box(6);

            // Preallocate all memory we will need.
            let mut skip = 3usize.pow(n);
            let mut buffer = Vec::with_capacity(skip);
            unsafe {
                // Safety: Eventually the entire vector will be initialized.
                // Before that, no uninitialized cells are read.
                buffer.set_len(skip);
            }

            // Arbitrary first triangle.
            buffer[0] = Triangle {
                a: Pos { x: 0.0, y: 0.0 },
                b: Pos { x: 1.0, y: 0.0 },
                c: Pos { x: 0.5, y: f64::sqrt(1.0 - 0.5 * 0.5) },
            };

            // Generate triangles in place, n iterations.
            for _ in 0..n {
                let mut i = 0;
                skip /= 3;
                while i < buffer.len() {
                    let parent = buffer[i];
                    buffer[i] = Triangle {
                        a: parent.a,
                        b: parent.a.mid(parent.b),
                        c: parent.a.mid(parent.c),
                    };
                    i += skip;
                    unsafe {
                        // Safety: Well aligned, not out of bounds.
                        ptr::write(buffer.as_mut_ptr().offset(i as isize), Triangle {
                            a: parent.a.mid(parent.b),
                            b: parent.b,
                            c: parent.b.mid(parent.c),
                        });
                    }
                    i += skip;
                    unsafe {
                        // Safety: Well aligned, not out of bounds.
                        ptr::write(buffer.as_mut_ptr().offset(i as isize), Triangle {
                            a: parent.a.mid(parent.c),
                            b: parent.b.mid(parent.c),
                            c: parent.c,
                        });
                    }
                    i += skip;
                }
            }

            black_box(buffer);
        });
    });
}

criterion_group!(benches, bench_sierpinski);
criterion_main!(benches);

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source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
dependencies = [
 "winapi",
]

[[package]]
name = "winapi-x86_64-pc-windows-gnu"
version = "0.4.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"

Cargo.toml

[package]
name = "sierpisnki"
version = "0.1.0"
authors = ["Niklas Fiekas <niklas.fiekas@backscattering.de>"]
edition = "2018"

[[bench]]
name = "benches"
harness = false
path = "benches.rs"

[lib]
bench = false
path = "lib.rs"

[dev-dependencies]
criterion = "0.3.3"

lib.rs