mandelbrot Rust program

// The Computer Language Benchmarks Game
// https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
//
// contributed by Matt Watson
// contributed by TeXitoi

use std::io::Write;
use std::thread;
const THREADS: usize = 20;
const MAX_ITER: usize = 50;
const VLEN: usize = 8;
const ZEROS: Vecf64 = [0.0; VLEN];

pub type Vecf64 = [f64; VLEN];

fn mul2 (x: Vecf64, y: Vecf64) -> Vecf64 {
    let mut res = ZEROS;
    for i in 0..VLEN { res[i] = x[i] * y[i]; }
    res
}
fn add2 (x: Vecf64, y: Vecf64) -> Vecf64 {
    let mut res = ZEROS;
    for i in 0..VLEN { res[i] = x[i] + y[i]; }
    res
}
fn sub2 (x: Vecf64, y: Vecf64) -> Vecf64 {
    let mut res = ZEROS;
    for i in 0..VLEN { res[i] = x[i] - y[i]; }
    res
}

pub fn mbrot8(cr: Vecf64, ci: Vecf64) -> u8 {
    let mut zr = cr;
    let mut zi = ci;
    let mut esc_bits = 0;
    for _ in 0..MAX_ITER {
        // Find Re(z)^2 and Im(z)^2
        let rr  = mul2(zr,zr);
        let ii  = mul2(zi,zi);
        // Check if we escape
        // May as well store this info in
        // same byte as output
        let mag = add2(rr, ii);
        for i in 0..VLEN {
            if mag[i] > 4.0 { esc_bits |= 128 >> i; }
        }
        // If no more work, break early
        if esc_bits == 0xff { break; }
        // Find Im(z^2)
        let ir = mul2(zr, zi);
        // Set Re(z^2)
        zr = sub2(rr, ii);
        // Set Im(z^2)
        zi = add2(ir, ir);
        // Add c
        zr = add2(zr, cr);
        zi = add2(zi, ci);
    }
    !esc_bits
}

fn main() {
    let size = std::env::args_os().nth(1)
        .and_then(|s| s.into_string().ok())
        .and_then(|n| n.parse().ok())
        .unwrap_or(200);
    let inv = 2.0 / size as f64;
    let mut xvals = vec![0.0; size];
    let mut yvals = vec![0.0; size];
    for i in 0..size {
        xvals[i] = i as f64 * inv - 1.5;
        yvals[i] = i as f64 * inv - 1.0;
    }
    let xloc = &xvals;
    let yloc = &yvals;

    assert!(size % THREADS == 0);// FIXME
    let handles: Vec<_> = (0..THREADS).map(|e| {
        let xloc = xloc.to_vec();
        let yloc = yloc.to_vec();
        thread::spawn(move || {
            let mut rows = vec![vec![0 as u8; size / 8]; size / THREADS];
            for y in 0..size / THREADS {
                for x in 0..size / 8 {
                    let mut cr = ZEROS;
                    let ci = [yloc[y + e * size / THREADS]; VLEN];
                    for i in 0..VLEN {
                        cr[i] = xloc[8 * x + i];
                    }
                    rows[y][x] = mbrot8(cr, ci);
                }
            }
            rows
        })
    }).collect();

    println!("P4\n{} {}", size, size);
    let stdout_unlocked = std::io::stdout();
    let mut stdout = stdout_unlocked.lock();
    for row in handles.into_iter().flat_map(|h| h.join().unwrap().into_iter()) {
        stdout.write_all(&row).unwrap();
    }
    stdout.flush().unwrap();
}
    

NOTES:
64-bit Ubuntu quad core
rustc 1.44.0 (49cae5576 2020-06-01)
LLVM version: 9.0


Fri, 05 Jun 2020 20:31:06 GMT

MAKE:
/opt/src/rust-1.44.0/bin/rustc -C opt-level=3 -C target-cpu=core2 -C lto -C codegen-units=1 -L /opt/src/rust-libs --extern futures=/opt/src/rust-libs/libfutures-ad0a024e469c2676.rlib mandelbrot.rs -o mandelbrot.rust_run
rm mandelbrot.rs

15.43s to complete and log all make actions

COMMAND LINE:
./mandelbrot.rust_run 16000

(BINARY) PROGRAM OUTPUT NOT SHOWN