library/std/src/sys/common/alloc.rs

use crate::alloc::{GlobalAlloc, Layout, System};
use crate::cmp;
use crate::ptr;

// The minimum alignment guaranteed by the architecture. This value is used to
// add fast paths for low alignment values.
#[cfg(all(any(
    target_arch = "x86",
    target_arch = "arm",
    target_arch = "mips",
    target_arch = "powerpc",
    target_arch = "powerpc64",
    target_arch = "sparc",
    target_arch = "asmjs",
    target_arch = "wasm32",
    target_arch = "hexagon",
    target_arch = "riscv32"
)))]
pub const MIN_ALIGN: usize = 8;
#[cfg(all(any(
    target_arch = "x86_64",
    target_arch = "aarch64",
    target_arch = "mips64",
    target_arch = "s390x",
    target_arch = "sparc64",
    target_arch = "riscv64"
)))]
pub const MIN_ALIGN: usize = 16;

pub unsafe fn realloc_fallback(
    alloc: &System,
    ptr: *mut u8,
    old_layout: Layout,
    new_size: usize,
) -> *mut u8 {
    // Docs for GlobalAlloc::realloc require this to be valid:
    let new_layout = Layout::from_size_align_unchecked(new_size, old_layout.align());

    let new_ptr = GlobalAlloc::alloc(alloc, new_layout);
    if !new_ptr.is_null() {
        let size = cmp::min(old_layout.size(), new_size);
        ptr::copy_nonoverlapping(ptr, new_ptr, size);
        GlobalAlloc::dealloc(alloc, ptr, old_layout);
    }
    new_ptr
}