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feat: optimize optional padding #2

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merged 4 commits into from
Oct 28, 2024
Merged

feat: optimize optional padding #2

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84a31d8
feat: optimize padding
saleel Oct 25, 2024
e572b5a
feat: assert output length
saleel Oct 25, 2024
e8cd187
fix: fix input/ouput length assertion on non pad
saleel Oct 28, 2024
1af23d0
fix: formattin
saleel Oct 28, 2024
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33 changes: 29 additions & 4 deletions src/encoder.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,29 @@ impl Base64EncodeBE {
// 240 bits fits 40 6-bit chunks and 30 8-bit chunks
// we pack 40 base64 values into a field element and convert into 30 bytes
// TODO: once we support arithmetic ops on generics, derive OutputBytes from InputBytes
// Calculate the number of padding characters and the length of the output without padding
let rem = InputBytes % 3;
let num_padding_chars = if rem == 1 {
2
} else if rem == 2 {
1
} else {
0
};
Comment on lines +64 to +70
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nice, I didn't realize we could do this in Noir. I must've tried to do an if let and been denied

let non_padded_output_length = OutputElements - num_padding_chars;

// Assert that the output length is correct
if self.pad {
assert((InputBytes + 2) / 3 * 4 == OutputElements, "invalid output length");
} else {
assert(
((InputBytes + 2) / 3 * 4) - num_padding_chars == OutputElements,
"invalid output length",
);
}

let mut result: [u8; OutputElements] = [0; OutputElements];

let BASE64_ELEMENTS_PER_CHUNK: u32 = 40;
let BYTES_PER_CHUNK: u32 = 30;
let num_chunks =
Expand Down Expand Up @@ -103,7 +125,10 @@ impl Base64EncodeBE {
// extract the 6-bit values from the Field element
let slice_base64_chunks: [u8; 40] = slice.to_be_radix(64);
for i in 0..num_elements_in_final_chunk {
result[base64_offset + i] = slice_base64_chunks[i];
// If padding is enabled, we can skip setting the last `non_padded_output_length` chars
if (!self.pad | base64_offset + i < non_padded_output_length) {
result[base64_offset + i] = slice_base64_chunks[i];
}
}

result = self.encode_elements(result);
Expand All @@ -112,10 +137,10 @@ impl Base64EncodeBE {
// handle padding
let rem = InputBytes % 3;
if (rem == 1) {
result[base64_offset + num_elements_in_final_chunk - 1] = BASE64_PADDING_CHAR;
result[base64_offset + num_elements_in_final_chunk - 2] = BASE64_PADDING_CHAR;
result[OutputElements - 1] = BASE64_PADDING_CHAR;
result[OutputElements - 2] = BASE64_PADDING_CHAR;
} else if (rem == 2) {
result[base64_offset + num_elements_in_final_chunk - 1] = BASE64_PADDING_CHAR;
result[OutputElements - 1] = BASE64_PADDING_CHAR;
}
}
}
Expand Down
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