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fix(datagen): use an aligned buffer when generating random bytes arrays #7919

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fix(datagen): use an aligned buffer when generating random bytes arrays #7919

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28 changes: 24 additions & 4 deletions rust/lance-datagen/src/generator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use std::{collections::HashMap, iter, marker::PhantomData, sync::Arc, sync::Lazy

use arrow::{
array::{ArrayData, AsArray, Float32Builder, GenericBinaryBuilder, GenericStringBuilder},
buffer::{BooleanBuffer, Buffer, OffsetBuffer, ScalarBuffer},
buffer::{BooleanBuffer, Buffer, MutableBuffer, OffsetBuffer, ScalarBuffer},
datatypes::{
ArrowPrimitiveType, Float32Type, Int32Type, Int64Type, IntervalDayTime,
IntervalMonthDayNano, UInt32Type,
Expand Down Expand Up @@ -814,9 +814,11 @@ impl<T: ArrowPrimitiveType + Send + Sync> ArrayGenerator for RandomBytesGenerato
rng: &mut rand_xoshiro::Xoshiro256PlusPlus,
) -> Result<Arc<dyn arrow_array::Array>, ArrowError> {
let num_bytes = length.0 * Self::byte_width()?;
let mut bytes = vec![0; num_bytes as usize];
rng.fill_bytes(&mut bytes);
let bytes = ScalarBuffer::new(Buffer::from(bytes), 0, length.0 as usize);
// A Vec<u8> is only guaranteed byte alignment, use MutableBuffer to get
// an allocation aligned for T::Native
let mut bytes = MutableBuffer::from_len_zeroed(num_bytes as usize);
rng.fill_bytes(bytes.as_slice_mut());
let bytes = ScalarBuffer::new(bytes.into(), 0, length.0 as usize);
Ok(Arc::new(
PrimitiveArray::<T>::new(bytes, None).with_data_type(self.data_type.clone()),
))
Expand Down Expand Up @@ -3527,6 +3529,24 @@ mod tests {
}
}

#[test]
fn test_rand_bytes_zero_rows() {
let mut rng = rand_xoshiro::Xoshiro256PlusPlus::seed_from_u64(DEFAULT_SEED.0);
// These types are generated from raw bytes and used to panic on empty
// arrays because a Vec<u8> is not sufficiently aligned for them
for data_type in [
DataType::Float16,
DataType::Decimal128(38, 10),
DataType::Decimal256(76, 10),
] {
let mut genn = array::rand_type(&data_type);
let arr = genn.generate(RowCount::from(0), &mut rng).unwrap();
assert_eq!(arr.len(), 0);
let arr = genn.generate(RowCount::from(3), &mut rng).unwrap();
assert_eq!(arr.len(), 3);
}
}

#[test]
fn test_rand_schema() {
let schema = Schema::new(vec![
Expand Down
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