Calculating primes

.gitignore

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+/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "primes"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "primes"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/main.rs

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+const SEGMENT_MAX: usize = 8;
+const SEGMENT_SIZE: usize = SEGMENT_MAX*SEGMENT_MAX;
+
+// Calculates the primes in the first segment using the simple sieve
+// Returns the primes in the primes array with n being the number of found primes
+fn simple_sieve(primes: &mut [usize; SEGMENT_SIZE], n: &mut usize) {
+    let mut segment = [true; SEGMENT_SIZE];
+    segment[0] = false;
+    segment[1] = false;
+
+    for x in 2..SEGMENT_MAX {
+        if segment[x] {
+            for y in ((x * x)..SEGMENT_SIZE).step_by(x) {
+                segment[y] = false;
+            }
+        }
+    }
+    let mut index = 0;
+    for (x,prime) in segment.iter().enumerate() {
+        if *prime {
+            primes[index] = x;
+            index += 1;
+        }
+    }
+    *n = index;
+}
+
+fn segment_sieve(primes: &[usize], prime_multiple: &mut [usize]) {
+    let mut low: usize = SEGMENT_SIZE;
+    let mut high: usize = SEGMENT_SIZE*2;
+    for _ in 1..SEGMENT_SIZE { // there are [SEGMENT_SIZE] number of segments
+        let mut segment = [true; SEGMENT_SIZE];
+        for (i,p) in primes.iter().enumerate() {
+            let mut multiple = prime_multiple[i];
+            while multiple < high {
+                segment[multiple-low] = false;
+                multiple += *p;
+            }
+            prime_multiple[i] = multiple;
+        }
+
+        for (x,prime) in segment.iter().enumerate() {
+            if *prime {
+                println!("{},", low+x);
+            }
+        }
+
+        low = high;
+        high += SEGMENT_SIZE;
+    }
+}
+
+fn main() {
+    // There will be no more than [SEGMENT_SIZE] primes in the segment
+    let mut primes_buffer = [0; SEGMENT_SIZE];
+    let mut n = 0;
+    simple_sieve(&mut primes_buffer, &mut n);
+
+    let primes = &primes_buffer[..n];
+
+    let mut prime_multiple = [0; SEGMENT_SIZE];
+    for (i,x) in primes.iter().enumerate() {
+        println!("{},", x);
+        let mut multiple = *x;
+        while multiple < SEGMENT_SIZE {
+            multiple += x;
+        }
+        prime_multiple[i] = multiple;
+    }
+    segment_sieve(primes, &mut prime_multiple);
+    println!();
+}