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🩹 Confine the zero-count early-out to the half-float path #75

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🩹 Confine the zero-count early-out to the half-float path #75

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23 changes: 18 additions & 5 deletions src/reader.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -229,9 +229,12 @@ impl<R: Read + Seek> VdbReader<R> {
gd: &GridDescriptor,
count: usize,
) -> Result<Vec<T>, ParseError> {
if count == 0 {
return Ok(Vec::new());
}
// NOTE: Deliberately no `count == 0` early-out here. OpenVDB's
// `readData()` -> `bloscFromStream()`/`unzipFromStream()` always consume
// the block's `i64` size header (and its payload) regardless of `count`,
// so returning early would leave the reader positioned mid-block and
// desync every subsequent read. The only place OpenVDB skips the stream
// is the half-float branch in `read_compressed()`.
Ok(if gd.compression.contains(Compression::BLOSC) {
let num_compressed_bytes = reader.read_i64::<LittleEndian>()?;
let compressed_count = num_compressed_bytes / std::mem::size_of::<T>() as i64;
Expand Down Expand Up @@ -358,8 +361,18 @@ impl<R: Read + Seek> VdbReader<R> {
let data = if gd.meta_data.is_half_float()
&& std::any::TypeId::of::<T>() == std::any::TypeId::of::<f32>()
{
let data = Self::read_compressed_data::<f16>(reader, archive, gd, count)?;
bytemuck::cast_vec(data.into_iter().map(f16::to_f32).collect::<Vec<f32>>())
// OpenVDB only skips the read for half-float grids, in
// `HalfReader</*IsReal=*/true, T>::read()`, which bails on `count < 1`
// before touching the stream. Every other path goes through
// `readData()`, which always consumes a block, so the early-out must
// stay confined to this branch -- see the comment in
// `read_compressed_data()`.
if count == 0 {
Vec::new()
} else {
let data = Self::read_compressed_data::<f16>(reader, archive, gd, count)?;
bytemuck::cast_vec(data.into_iter().map(f16::to_f32).collect::<Vec<f32>>())
}
} else if !gd.meta_data.is_half_float()
&& std::any::TypeId::of::<T>() == std::any::TypeId::of::<f16>()
{
Expand Down
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