Zig Prime Sieve

sieve.zig

const std = @import("std");

pub fn main(init: std.process.Init) !void {
    const args = try init.minimal.args.toSlice(init.arena.allocator());

    const limit: usize = if (args.len >= 2)
        try std.fmt.parseInt(usize, args[1], 10)
    else
        10_000_000;

    const is_prime = try init.gpa.alloc(bool, limit + 1);
    defer init.gpa.free(is_prime);

    @memset(is_prime, true);
    is_prime[0] = false;
    if (limit >= 1)
        is_prime[1] = false;

    var p: usize = 2;
    while (p <= limit / p) : (p += 1) {
        if (is_prime[p]) {
            var i: usize = p * p;
            while (i <= limit) : (i += p) {
                is_prime[i] = false;
            }
        }
    }

    var count: usize = 0;
    for (is_prime) |prime| {
        if (prime) count += 1;
    }

    std.debug.print("Number of primes up to {d} is: {d}\n", .{ limit, count });
}