}};
}
-/// Loads up to 8 bytes from a byte-slice into a little-endian u64.
-#[inline]
-fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
- assert!(len <= 8 && start + len <= buf.len());
+/// Loads an integer of the desired type from a byte stream, in LE order. Uses
+/// `copy_nonoverlapping` to let the compiler generate the most efficient way
+/// to load it from a possibly unaligned address.
+///
+/// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
+macro_rules! load_int_le {
+ ($buf:expr, $i:expr, $int_ty:ident) => {{
+ debug_assert!($i + mem::size_of::<$int_ty>() <= $buf.len());
+ let mut data = 0 as $int_ty;
+ ptr::copy_nonoverlapping(
+ $buf.get_unchecked($i),
+ &mut data as *mut _ as *mut u8,
+ mem::size_of::<$int_ty>(),
+ );
+ data.to_le()
+ }};
+}
- let mut out = 0u64;
- unsafe {
- let out_ptr = &mut out as *mut _ as *mut u8;
- ptr::copy_nonoverlapping(buf.as_ptr().offset(start as isize), out_ptr, len);
+/// Loads a u64 using up to 7 bytes of a byte slice. It looks clumsy but the
+/// `copy_nonoverlapping` calls that occur (via `load_int_le!`) all have fixed
+/// sizes and avoid calling `memcpy`, which is good for speed.
+///
+/// Unsafe because: unchecked indexing at start..start+len
+#[inline]
+unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
+ debug_assert!(len < 8);
+ let mut i = 0; // current byte index (from LSB) in the output u64
+ let mut out = 0;
+ if i + 3 < len {
+ out = load_int_le!(buf, start + i, u32) as u64;
+ i += 4;
+ }
+ if i + 1 < len {
+ out |= (load_int_le!(buf, start + i, u16) as u64) << (i * 8);
+ i += 2
+ }
+ if i < len {
+ out |= (*buf.get_unchecked(start + i) as u64) << (i * 8);
+ i += 1;
}
- out.to_le()
+ debug_assert_eq!(i, len);
+ out
}
impl SipHasher128 {
if self.ntail != 0 {
needed = 8 - self.ntail;
- self.tail |= u8to64_le(msg, 0, cmp::min(length, needed)) << (8 * self.ntail);
+ self.tail |= unsafe { u8to64_le(msg, 0, cmp::min(length, needed)) } << (8 * self.ntail);
if length < needed {
self.ntail += length;
return;
let mut i = needed;
while i < len - left {
- let mi = u8to64_le(msg, i, 8);
+ let mi = unsafe { load_int_le!(msg, i, u64) };
self.state.v3 ^= mi;
Sip24Rounds::c_rounds(&mut self.state);
i += 8;
}
- self.tail = u8to64_le(msg, i, left);
+ self.tail = unsafe { u8to64_le(msg, i, left) };
self.ntail = left;
}