Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Use zerocopy to replace some unsafe code #1349

Merged
merged 1 commit into from
Nov 2, 2023
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension


Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
3 changes: 2 additions & 1 deletion Cargo.toml
Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ alloc = ["rand_core/alloc"]
getrandom = ["rand_core/getrandom"]

# Option (requires nightly Rust): experimental SIMD support
simd_support = []
simd_support = ["zerocopy/simd-nightly"]

# Option (enabled by default): enable StdRng
std_rng = ["rand_chacha"]
Expand All @@ -69,6 +69,7 @@ rand_core = { path = "rand_core", version = "0.7.0" }
log = { version = "0.4.4", optional = true }
serde = { version = "1.0.103", features = ["derive"], optional = true }
rand_chacha = { path = "rand_chacha", version = "0.4.0", default-features = false, optional = true }
zerocopy = { version = "0.7.20", default-features = false, features = ["simd"] }

[target.'cfg(unix)'.dependencies]
# Used for fork protection (reseeding.rs)
Expand Down
1 change: 1 addition & 0 deletions rand_core/Cargo.toml
Original file line number Diff line number Diff line change
Expand Up @@ -32,3 +32,4 @@ serde1 = ["serde"] # enables serde for BlockRng wrapper
[dependencies]
serde = { version = "1", features = ["derive"], optional = true }
getrandom = { version = "0.2", optional = true }
zerocopy = { version = "0.7.20", default-features = false }
18 changes: 3 additions & 15 deletions rand_core/src/impls.rs
Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@

use crate::RngCore;
use core::cmp::min;
use zerocopy::AsBytes;

/// Implement `next_u64` via `next_u32`, little-endian order.
pub fn next_u64_via_u32<R: RngCore + ?Sized>(rng: &mut R) -> u64 {
Expand Down Expand Up @@ -52,31 +53,18 @@ pub fn fill_bytes_via_next<R: RngCore + ?Sized>(rng: &mut R, dest: &mut [u8]) {
}
}

trait Observable: Copy {
trait Observable: AsBytes + Copy {
fn to_le(self) -> Self;

// Contract: observing self is memory-safe (implies no uninitialised padding)
fn as_byte_slice(x: &[Self]) -> &[u8];
}
impl Observable for u32 {
fn to_le(self) -> Self {
self.to_le()
}
fn as_byte_slice(x: &[Self]) -> &[u8] {
let ptr = x.as_ptr() as *const u8;
let len = x.len() * core::mem::size_of::<Self>();
unsafe { core::slice::from_raw_parts(ptr, len) }
}
}
impl Observable for u64 {
fn to_le(self) -> Self {
self.to_le()
}
fn as_byte_slice(x: &[Self]) -> &[u8] {
let ptr = x.as_ptr() as *const u8;
let len = x.len() * core::mem::size_of::<Self>();
unsafe { core::slice::from_raw_parts(ptr, len) }
}
}

/// Fill dest from src
Expand All @@ -98,7 +86,7 @@ fn fill_via_chunks<T: Observable>(src: &mut [T], dest: &mut [u8]) -> (usize, usi
}
}

dest[..byte_len].copy_from_slice(&T::as_byte_slice(&src[..num_chunks])[..byte_len]);
dest[..byte_len].copy_from_slice(&<[T]>::as_bytes(&src[..num_chunks])[..byte_len]);

(num_chunks, byte_len)
}
Expand Down
3 changes: 1 addition & 2 deletions src/distributions/integer.rs
Original file line number Diff line number Diff line change
Expand Up @@ -134,8 +134,7 @@ macro_rules! x86_intrinsic_impl {
let mut buf = [0_u8; mem::size_of::<$intrinsic>()];
rng.fill_bytes(&mut buf);
// x86 is little endian so no need for conversion
// SAFETY: we know [u8; N] and $intrinsic have the same size
unsafe { mem::transmute_copy(&buf) }
zerocopy::transmute!(buf)
Comment on lines 134 to +137
Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Here's another option if this would be preferred. I opted not to go this route since it messes with code that's been verified to compile to SIMD instructions (although I expect the same would work here):

let mut val = $intrinsic::new_zeroed();
// On proper hardware, this should compile to SIMD instructions
// Verified on x86 Haswell with __m128i, __m256i
//
// x86 is little endian so no need for conversion
rng.fill_bytes(&mut val.as_bytes_mut());
val

}
}
)+};
Expand Down