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//! Implementation for WASI Preview 2.
use crate::Error;
use core::mem::MaybeUninit;
use wasi::random::random::get_random_u64;
#[inline]
pub fn inner_u32() -> Result<u32, Error> {
let val = get_random_u64();
Ok(crate::util::truncate(val))
}
#[inline]
pub fn inner_u64() -> Result<u64, Error> {
Ok(get_random_u64())
}
#[inline]
pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
use core::ptr::copy_nonoverlapping;
use wasi::random::random::get_random_u64;
let (prefix, chunks, suffix) = unsafe { dest.align_to_mut::<MaybeUninit<u64>>() };
// We use `get_random_u64` instead of `get_random_bytes` because the latter creates
// an allocation due to the Wit IDL [restrictions][0]. This should be fine since
// the main use case of `getrandom` is seed generation.
//
// [0]: https://github.com/WebAssembly/wasi-random/issues/27
if !prefix.is_empty() {
let val = get_random_u64();
let src = (&val as *const u64).cast();
unsafe {
copy_nonoverlapping(src, prefix.as_mut_ptr(), prefix.len());
}
}
for dst in chunks {
dst.write(get_random_u64());
}
if !suffix.is_empty() {
let val = get_random_u64();
let src = (&val as *const u64).cast();
unsafe {
copy_nonoverlapping(src, suffix.as_mut_ptr(), suffix.len());
}
}
Ok(())
}
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