stumpalo 0.5.0

A fast, zero-dependency, memory efficient bump allocator with chunk reuse and scoped stack support
Documentation 
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// Maximum address in the userspace virtual address range.
// Uses the largest standard configuration to ensure correctness across all systems.

use crate::chunk::HEADER_SIZE;

// Supports both 4-level (48-bit) and 5-level (57-bit) paging.
// Use 57-bit limit (128 PiB) as the safe, universal maximum.
#[cfg(target_arch = "x86_64")]
pub(crate) const MAX_USABLE: usize = (1 << 57) - 1;

// Supports configurations up to 52-bit virtual address space (4 PiB).
#[cfg(target_arch = "aarch64")]
pub(crate) const MAX_USABLE: usize = (1 << 52) - 1;

// Supports standard 48-bit Sv48 and upcoming 57-bit Sv57 modes.
// Use 57-bit limit as the safe, universal maximum.
#[cfg(target_arch = "riscv64")]
pub(crate) const MAX_USABLE: usize = (1 << 57) - 1;

#[cfg(not(any(
    target_arch = "x86_64",
    target_arch = "aarch64",
    target_arch = "riscv64"
)))]
// Fallback for unknown architectures. Will result in an extra conditional branch in the fast path.
// Not a big deal.
pub(crate) const MAX_USABLE: usize = usize::MAX;

pub(crate) const SAFE_SIZE: usize = usize::MAX - MAX_USABLE;

// The absolute minimum address that the header can live at
// is at 0x10, as 0x00 is guaranteed to not be valid, and
// we allocate chunks that are 16-byte aligned.
// This means that the absolute minimum address that `top`
// can start at is 0x20.
pub(crate) const MIN_TOP: usize = HEADER_SIZE * 2;