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chacha20: rng - Fixing NEON Backend #390

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chacha20: rng - Fixing NEON Backend #390

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b9f57a9
added test
nstilt1 Feb 6, 2025
6c64360
fixed 64-bit addition
nstilt1 Feb 6, 2025
4c5398f
added 2 more endian tests just to be sure; they passed
nstilt1 Feb 6, 2025
0372400
fmt
nstilt1 Feb 6, 2025
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31 changes: 11 additions & 20 deletions chacha20/src/backends/neon.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -88,15 +88,6 @@ impl<R: Rounds> ParBlocksSizeUser for Backend<R> {
type ParBlocksSize = U4;
}

macro_rules! add64 {
($a:expr, $b:expr) => {
vreinterpretq_u32_u64(vaddq_u64(
vreinterpretq_u64_u32($a),
vreinterpretq_u64_u32($b),
))
};
}

/// Evaluates to `a = a + b`, where the operands are u32x4s
macro_rules! add_assign_vec {
($a:expr, $b:expr) => {
Expand All @@ -113,7 +104,7 @@ impl<R: Rounds> StreamCipherBackend for Backend<R> {
self.gen_par_ks_blocks(&mut par);
*block = par[0];
unsafe {
self.state[3] = add64!(state3, vld1q_u32([1, 0, 0, 0].as_ptr()));
self.state[3] = vaddq_u32(state3, vld1q_u32([1, 0, 0, 0].as_ptr()));
}
}

Expand All @@ -126,19 +117,19 @@ impl<R: Rounds> StreamCipherBackend for Backend<R> {
self.state[0],
self.state[1],
self.state[2],
add64!(self.state[3], self.ctrs[0]),
vaddq_u32(self.state[3], self.ctrs[0]),
],
[
self.state[0],
self.state[1],
self.state[2],
add64!(self.state[3], self.ctrs[1]),
vaddq_u32(self.state[3], self.ctrs[1]),
],
[
self.state[0],
self.state[1],
self.state[2],
add64!(self.state[3], self.ctrs[2]),
vaddq_u32(self.state[3], self.ctrs[2]),
],
];

Expand All @@ -152,7 +143,7 @@ impl<R: Rounds> StreamCipherBackend for Backend<R> {
add_assign_vec!(blocks[block][state_row], self.state[state_row]);
}
if block > 0 {
blocks[block][3] = add64!(blocks[block][3], self.ctrs[block - 1]);
blocks[block][3] = vaddq_u32(blocks[block][3], self.ctrs[block - 1]);
}
// write blocks to dest
for state_row in 0..4 {
Expand All @@ -162,7 +153,7 @@ impl<R: Rounds> StreamCipherBackend for Backend<R> {
);
}
}
self.state[3] = add64!(self.state[3], self.ctrs[3]);
self.state[3] = vaddq_u32(self.state[3], self.ctrs[3]);
}
}
}
Expand Down Expand Up @@ -205,19 +196,19 @@ impl<R: Rounds> Backend<R> {
self.state[0],
self.state[1],
self.state[2],
add64!(self.state[3], self.ctrs[0]),
vaddq_u32(self.state[3], self.ctrs[0]),
],
[
self.state[0],
self.state[1],
self.state[2],
add64!(self.state[3], self.ctrs[1]),
vaddq_u32(self.state[3], self.ctrs[1]),
],
[
self.state[0],
self.state[1],
self.state[2],
add64!(self.state[3], self.ctrs[2]),
vaddq_u32(self.state[3], self.ctrs[2]),
],
];

Expand All @@ -232,7 +223,7 @@ impl<R: Rounds> Backend<R> {
add_assign_vec!(blocks[block][state_row], self.state[state_row]);
}
if block > 0 {
blocks[block][3] = add64!(blocks[block][3], self.ctrs[block - 1]);
blocks[block][3] = vaddq_u32(blocks[block][3], self.ctrs[block - 1]);
}
// write blocks to buffer
for state_row in 0..4 {
Expand All @@ -243,7 +234,7 @@ impl<R: Rounds> Backend<R> {
}
dest_ptr = dest_ptr.add(64);
}
self.state[3] = add64!(self.state[3], self.ctrs[3]);
self.state[3] = vaddq_u32(self.state[3], self.ctrs[3]);
}
}

Expand Down
25 changes: 25 additions & 0 deletions chacha20/src/rng.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1114,5 +1114,30 @@ pub(crate) mod tests {
rng.set_stream([3, 3333, 333333]);
let expected = 2059058063;
assert_eq!(rng.next_u32(), expected);
rng.set_stream(1234567);
let expected = 1254506509;
assert_eq!(rng.next_u32(), expected);
rng.set_stream([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]);
let expected = 1391671567;
assert_eq!(rng.next_u32(), expected);
}

/// If this test fails, the backend may be
/// performing 64-bit addition.
#[test]
fn counter_wrapping() {
let mut rng = ChaChaRng::from_seed([0u8; 32]);

// get first four blocks and word pos
let mut first_blocks = [0u8; 64 * 4];
rng.fill_bytes(&mut first_blocks);
let word_pos = rng.get_word_pos();

// get first four blocks after wrapping
rng.set_block_pos(u32::MAX);
let mut result = [0u8; 64 * 5];
rng.fill_bytes(&mut result);
assert_eq!(word_pos, rng.get_word_pos());
assert_eq!(&first_blocks[0..64 * 4], &result[64..]);
}
}