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perf: optimize push_slice #3393

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perf: optimize push_slice #3393

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23339e1
optimize push_slice
malik672 Feb 2, 2026
e9bdc06
fix test
malik672 Feb 2, 2026
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97 changes: 82 additions & 15 deletions crates/interpreter/src/interpreter/stack.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -343,32 +343,99 @@ impl Stack {
let dst = self.data.as_mut_ptr().add(self.data.len()).cast::<u64>();
self.data.set_len(new_len);

let mut i = 0;
let mut i: usize = 0;

// Write full words
let words = slice.chunks_exact(32);
let partial_last_word = words.remainder();
for word in words {
// Note: We unroll `U256::from_be_bytes` here to write directly into the buffer,
// instead of creating a 32 byte array on the stack and then copying it over.
for l in word.rchunks_exact(8) {
dst.add(i).write(u64::from_be_bytes(l.try_into().unwrap()));
i += 1;
}
let num_full_words = slice.len() / 32;
let partial_start = num_full_words * 32;

for word_idx in 0..num_full_words {
let word_start = word_idx * 32;
// write 4 limbs (32 bytes) in reverse order for big-endian

let limb_start = word_start + 24;
let limb_bytes = [
slice[limb_start],
slice[limb_start + 1],
slice[limb_start + 2],
slice[limb_start + 3],
slice[limb_start + 4],
slice[limb_start + 5],
slice[limb_start + 6],
slice[limb_start + 7],
];
dst.add(i).write(u64::from_be_bytes(limb_bytes));

let limb_start = word_start + 16;
let limb_bytes = [
slice[limb_start],
slice[limb_start + 1],
slice[limb_start + 2],
slice[limb_start + 3],
slice[limb_start + 4],
slice[limb_start + 5],
slice[limb_start + 6],
slice[limb_start + 7],
];
dst.add(i + 1).write(u64::from_be_bytes(limb_bytes));

let limb_start = word_start + 8;
let limb_bytes = [
slice[limb_start],
slice[limb_start + 1],
slice[limb_start + 2],
slice[limb_start + 3],
slice[limb_start + 4],
slice[limb_start + 5],
slice[limb_start + 6],
slice[limb_start + 7],
];
dst.add(i + 2).write(u64::from_be_bytes(limb_bytes));

let limb_start = word_start;
let limb_bytes = [
slice[limb_start],
slice[limb_start + 1],
slice[limb_start + 2],
slice[limb_start + 3],
slice[limb_start + 4],
slice[limb_start + 5],
slice[limb_start + 6],
slice[limb_start + 7],
];
dst.add(i + 3).write(u64::from_be_bytes(limb_bytes));

i += 4;
}

let partial_last_word = &slice[partial_start..];
if partial_last_word.is_empty() {
return true;
}

// Write limbs of partial last word
let limbs = partial_last_word.rchunks_exact(8);
let partial_last_limb = limbs.remainder();
for l in limbs {
dst.add(i).write(u64::from_be_bytes(l.try_into().unwrap()));
// Write limbs of partial last word (process from end backwards)
let num_full_limbs = partial_last_word.len() / 8;
let partial_limb_len = partial_last_word.len() % 8;

// Process full 8-byte limbs from the end of the slice backwards
for limb_offset in 0..num_full_limbs {
let limb_start = partial_last_word.len() - (limb_offset + 1) * 8;
let limb_bytes = [
partial_last_word[limb_start],
partial_last_word[limb_start + 1],
partial_last_word[limb_start + 2],
partial_last_word[limb_start + 3],
partial_last_word[limb_start + 4],
partial_last_word[limb_start + 5],
partial_last_word[limb_start + 6],
partial_last_word[limb_start + 7],
];
dst.add(i).write(u64::from_be_bytes(limb_bytes));
i += 1;
}

let partial_last_limb = &partial_last_word[..partial_limb_len];

// Write partial last limb by padding with zeros
if !partial_last_limb.is_empty() {
let mut tmp = [0u8; 8];
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