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//! CPU specific funcitions

use core::arch::asm;
use core::iter::FusedIterator;
use core::mem::size_of;
use core::sync::atomic::{AtomicU32, Ordering};

use crate::MAX_CPUS;

use super::int::lapic::LAPIC;

static ONLINE_MASK: AtomicU32 = AtomicU32::new(0);
const _: () = assert!(MAX_CPUS <= size_of::<AtomicU32>() * 8);

/// Halt the cpu
pub fn halt() {
    unsafe { asm!("hlt", options(nomem, nostack)) };
}

/// Initialize the CPU
pub fn init(core: usize) {
    ONLINE_MASK.fetch_or(1 << core, Ordering::AcqRel);
}

/// Returns the CPU ID
pub fn id() -> usize {
    // In practice (single NUMA), the CPU numbers and LAPIC ids seem to be equal
    LAPIC.id() as _
}

/// Returns a bitmap of online CPUs
pub fn online() -> u32 {
    ONLINE_MASK.load(Ordering::Acquire)
}

/// Return an iterator over all online CPUs
pub fn iter() -> impl Iterator<Item = usize> {
    let mask = ONLINE_MASK.load(Ordering::Acquire);
    (0..MAX_CPUS).filter(move |i| mask & (1 << i) != 0)
}