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feat: optimize constraints in sha256 #6145

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Merged
TomAFrench merged 4 commits into from
Sep 24, 2024
Merged

feat: optimize constraints in sha256 #6145

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33fe6c4
feat: optimize constraints in sha256
TomAFrench Sep 24, 2024
a1b2f46
feat: remove unnecessary byte decomposition
TomAFrench Sep 24, 2024
9e66e9b
fix: bits vs bytes
TomAFrench Sep 24, 2024
16fbfd4
.
TomAFrench Sep 24, 2024
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15 changes: 7 additions & 8 deletions noir_stdlib/src/hash/sha256.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -186,18 +186,18 @@ pub fn sha256_var<let N: u32>(msg: [u8; N], message_size: u64) -> [u8; 32] {

if !crate::runtime::is_unconstrained() {
for i in 0..56 {
if i < msg_byte_ptr {
assert_eq(msg_block[i], last_block[i]);
} else {
assert_eq(msg_block[i], zero);
}
let predicate = (i < msg_byte_ptr) as u8;
let expected_byte = predicate * last_block[i];
assert_eq(msg_block[i], expected_byte);
}

// We verify the message length was inserted correctly by reversing the byte decomposition.
let len = 8 * message_size;
let len_bytes: [u8; 8] = (len as Field).to_be_bytes();
let mut reconstructed_len: Field = 0;
for i in 56..64 {
assert_eq(msg_block[i], len_bytes[i - 56]);
reconstructed_len = 256 * reconstructed_len + msg_block[i] as Field;
}
assert_eq(reconstructed_len, len as Field);
}

hash_final_block(msg_block, h)
Expand Down Expand Up @@ -254,4 +254,3 @@ fn hash_final_block(msg_block: [u8; 64], mut state: [u32; 8]) -> [u8; 32] {

out_h
}