zircon/kernel/lib/page/src/lib.rs

// Copyright 2026 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#![no_std]

// TODO(https://fxbug.dev/534566390): Extend this to support more generic page definitions. For now
// since the C++ side only supports 4k pages we can hard code the 4k constants here.

/// The selected page size.
pub const SIZE: usize = 4096;

/// The shift of the first level of virtual address mask used for page table walking.
pub const SHIFT: usize = 12;

/// Mask that will extract the offset into a page of an address.
pub const MASK: usize = 4095;

/// Returns true if `val` is aligned to a page boundary.
#[inline]
pub const fn is_aligned(val: usize) -> bool {
    (val & MASK) == 0
}

/// Rounds `val` down to the nearest page boundary.
#[inline]
pub const fn round_down(val: usize) -> usize {
    val & !MASK
}

/// Rounds `val` up to the nearest page boundary.
#[inline]
pub const fn round_up(val: usize) -> usize {
    (val + MASK) & !MASK
}