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#![no_std]
#![allow(unused)]

use core::arch::asm;

// Status register
#[cfg(not(portable_atomic_s_mode))]
macro_rules! status {
    () => {
        "mstatus"
    };
}
#[cfg(portable_atomic_s_mode)]
macro_rules! status {
    () => {
        "sstatus"
    };
}

// MIE (Machine Interrupt Enable) bit (1 << 3)
#[cfg(not(portable_atomic_s_mode))]
const MASK: State = 0x8;
#[cfg(not(portable_atomic_s_mode))]
macro_rules! mask {
    () => {
        "0x8"
    };
}
// SIE (Supervisor Interrupt Enable) bit (1 << 1)
#[cfg(portable_atomic_s_mode)]
const MASK: State = 0x2;
#[cfg(portable_atomic_s_mode)]
macro_rules! mask {
    () => {
        "0x2"
    };
}

#[cfg(target_arch = "riscv32")]
type State = u32;
#[cfg(target_arch = "riscv64")]
type State = u64;

/// Disables interrupts and returns the previous interrupt state.
#[inline]
fn disable() -> State {
    let r: State;
    // SAFETY: reading mstatus and disabling interrupts is safe.
    // (see module-level comments of interrupt/mod.rs on the safety of using privileged instructions)
    unsafe {
        // Do not use `nomem` and `readonly` because prevent subsequent memory accesses from being reordered before interrupts are disabled.
        asm!(concat!("csrrci {0}, ", status!(), ", ", mask!()), out(reg) r, options(nostack, preserves_flags));
    }
    r
}

/// Restores the previous interrupt state.
///
/// # Safety
///
/// The state must be the one retrieved by the previous `disable`.
#[inline]
unsafe fn restore(r: State) {
    if r & MASK != 0 {
        // SAFETY: the caller must guarantee that the state was retrieved by the previous `disable`,
        // and we've checked that interrupts were enabled before disabling interrupts.
        unsafe {
            // Do not use `nomem` and `readonly` because prevent preceding memory accesses from being reordered after interrupts are enabled.
            asm!(concat!("csrsi ", status!(), ", ", mask!()), options(nostack, preserves_flags));
        }
    }
}

#[inline]
fn with<F, R>(f: F) -> R
where
    F: FnOnce() -> R,
{
    // Get current interrupt state and disable interrupts
    let state = disable();

let r = f();

// Restore interrupt state
    // SAFETY: the state was retrieved by the previous `disable`.
    unsafe { restore(state) }

r
}
#[inline(never)]
pub fn example() {
    with(|| unsafe {
        asm!("nop", options(nostack, preserves_flags));
    });
}