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feat: swap endianness in-place in keccak implementation #6128

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Merged
TomAFrench merged 6 commits into from
Sep 23, 2024
Merged

feat: swap endianness in-place in keccak implementation #6128

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4c3b013
feat: remove unnecessary array allocation in keccak impl
TomAFrench Sep 23, 2024
23ecb2a
.
TomAFrench Sep 23, 2024
a1a7906
chore: improve naming and remove magic 7
TomAFrench Sep 23, 2024
432dd06
chore: use new naming consistently
TomAFrench Sep 23, 2024
10b9c7b
chore: merge for-loops
TomAFrench Sep 23, 2024
3efd419
chore: remove reordering of bytes
TomAFrench Sep 23, 2024
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26 changes: 6 additions & 20 deletions noir_stdlib/src/hash/keccak.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -35,40 +35,27 @@ pub(crate) fn keccak256<let N: u32>(input: [u8; N], message_size: u32) -> [u8; 3
block_bytes[message_size] = 1;
block_bytes[real_blocks_bytes - 1] = 0x80;

// keccak lanes interpret memory as little-endian integers,
// means we need to swap our byte ordering
let num_limbs = max_blocks * LIMBS_PER_BLOCK; //max_blocks_length / WORD_SIZE;
for i in 0..num_limbs {
let mut temp = [0; WORD_SIZE];
let word_size_times_i = WORD_SIZE * i;
for j in 0..WORD_SIZE {
temp[j] = block_bytes[word_size_times_i+j];
}
for j in 0..WORD_SIZE {
block_bytes[word_size_times_i + j] = temp[7 - j];
}
}

let mut sliced_buffer = Vec::new();
// populate a vector of 64-bit limbs from our byte array
for i in 0..num_limbs {
let word_size_times_i = i * WORD_SIZE;
let ws_times_i_plus_7 = word_size_times_i + 7;
let limb_start = WORD_SIZE * i;

let mut sliced = 0;
if (word_size_times_i + WORD_SIZE > max_blocks_length) {
let slice_size = max_blocks_length - word_size_times_i;
if (limb_start + WORD_SIZE > max_blocks_length) {
let slice_size = max_blocks_length - limb_start;
let byte_shift = (WORD_SIZE - slice_size) * 8;
let mut v = 1;
for k in 0..slice_size {
sliced += v * (block_bytes[ws_times_i_plus_7-k] as Field);
sliced += v * (block_bytes[limb_start+k] as Field);
v *= 256;
}
let w = 1 << (byte_shift as u8);
sliced *= w as Field;
} else {
let mut v = 1;
for k in 0..WORD_SIZE {
sliced += v * (block_bytes[ws_times_i_plus_7-k] as Field);
sliced += v * (block_bytes[limb_start+k] as Field);
v *= 256;
}
}
Expand Down Expand Up @@ -156,4 +143,3 @@ mod tests {
assert_eq(keccak256(input, 13), result);
}
}