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perf(value): avoid an unused byte in padded decoding #399

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perf(value): avoid an unused byte in padded decoding #399

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41 changes: 31 additions & 10 deletions src/value.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1034,13 +1034,15 @@ impl Value {
for _ in 0..ty.bit_width() / 8 {
blob.push(bits.read_u8()?);
}
let mut last = 0u8;
for i in 0..ty.bit_width() % 8 {
if bits.read_bit()? {
last |= 1 << (7 - i);
if ty.bit_width() % 8 != 0 {
let mut last = 0u8;
for i in 0..ty.bit_width() % 8 {
if bits.read_bit()? {
last |= 1 << (7 - i);
}
}
blob.push(last);
}
blob.push(last);

Ok(Value {
inner: blob.into(),
Expand Down Expand Up @@ -1389,11 +1391,30 @@ mod tests {

#[test]
fn padded_round_trip() {
let v = Value::u64(0xff00_00ff_ff00_00ff);
let (bits, _) = v.iter_padded().collect_bits();
let mut iter = BitIter::new(bits.into_iter());
let new_v = Value::from_padded_bits(&mut iter, &v.ty).unwrap();
assert_eq!(v, new_v);
for value in [
Value::unit(),
Value::u1(1),
Value::u4(6),
Value::u8(0xa5),
Value::u64(0xff00_00ff_ff00_00ff),
Value::some(Value::u8(0xa5)),
] {
let (bits, len) = value.iter_padded().collect_bits();
for offset in 0..8 {
let mut prefixed = vec![true; offset];
prefixed.extend(value.iter_padded());
let (bytes, _) = prefixed.into_iter().collect_bits();
let mut iter = BitIter::byte_slice_window(&bytes, offset, offset + len);
let decoded = Value::from_padded_bits(&mut iter, &value.ty).unwrap();
assert_eq!(decoded, value);
assert_eq!(decoded.inner.as_ref(), bits);
assert_eq!(iter.n_total_read(), len);
}
if !bits.is_empty() {
let mut truncated = BitIter::from(&bits[..bits.len() - 1]);
assert!(Value::from_padded_bits(&mut truncated, &value.ty).is_err());
}
}
}

// --- Bug regression tests for right_shift_1 when new_bit=false ---
Expand Down