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fix[bitpacking]: filter #6120

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Merged
joseph-isaacs merged 1 commit into from
Jan 23, 2026
Merged

fix[bitpacking]: filter #6120

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64 changes: 64 additions & 0 deletions encodings/fastlanes/src/bitpacking/compute/filter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -256,4 +256,68 @@ mod test {
let bitpacked = BitPackedArray::encode(unpacked.as_ref(), 3).unwrap();
test_filter_conformance(bitpacked.as_ref());
}

/// Regression test for signed integers with patches.
///
/// When filtering signed integers that have patches (exceptions), the patches
/// are stored with the signed type but FastLanes uses unsigned types internally.
/// This test ensures that the type handling is correct.
#[test]
fn filter_bitpacked_signed_with_patches() {
// Create signed integer values where some exceed the bit width (causing patches).
// Values 0-127 fit in 7 bits, but 1000 and 2000 do not.
let values: Vec<i32> = vec![0, 10, 1000, 20, 30, 2000, 40, 50, 60, 70];
let unpacked = PrimitiveArray::from_iter(values.clone());
let bitpacked = BitPackedArray::encode(unpacked.as_ref(), 7).unwrap();
assert!(
bitpacked.patches().is_some(),
"Expected patches for values exceeding bit width"
);

// Filter to include some patched and some non-patched values.
let filtered = filter(
bitpacked.as_ref(),
&Mask::from_indices(values.len(), vec![0, 2, 5, 9]),
)
.unwrap()
.to_primitive();

assert_arrays_eq!(filtered, PrimitiveArray::from_iter([0i32, 1000, 2000, 70]));
}

/// Regression test for signed integers with patches using low selectivity.
///
/// This test uses a low selectivity filter which takes a different code path
/// that doesn't fully decompress the array first.
#[test]
fn filter_bitpacked_signed_with_patches_low_selectivity() {
// Create a larger array with signed integers and some patches.
let values: Vec<i32> = (0..1000)
.map(|i| {
if i % 100 == 0 {
10000 + i // These will be patches (exceed 7 bits)
} else {
i % 128 // These fit in 7 bits
}
})
.collect();
let unpacked = PrimitiveArray::from_iter(values.clone());
let bitpacked = BitPackedArray::encode(unpacked.as_ref(), 7).unwrap();
assert!(
bitpacked.patches().is_some(),
"Expected patches for values exceeding bit width"
);

// Use low selectivity (only select 2% of values) to avoid full decompression.
let indices: Vec<usize> = (0..20).collect();
let filtered = filter(
bitpacked.as_ref(),
&Mask::from_indices(values.len(), indices),
)
.unwrap()
.to_primitive();

let expected: Vec<i32> = values[0..20].to_vec();
assert_arrays_eq!(filtered, PrimitiveArray::from_iter(expected));
}
}
110 changes: 28 additions & 82 deletions encodings/fastlanes/src/bitpacking/vtable/kernels/filter.rs
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Expand Up @@ -14,16 +14,15 @@ use vortex_array::kernel::ExecuteParentKernel;
use vortex_array::kernel::ParentKernelSet;
use vortex_array::matchers::Exact;
use vortex_array::validity::Validity;
use vortex_array::vtable::ValidityHelper;
use vortex_buffer::Buffer;
use vortex_buffer::BufferMut;
use vortex_compute::filter::Filter;
use vortex_dtype::NativePType;
use vortex_dtype::PType;
use vortex_dtype::UnsignedPType;
use vortex_dtype::match_each_integer_ptype;
use vortex_dtype::match_each_unsigned_integer_ptype;
use vortex_error::VortexResult;
use vortex_mask::Mask;
use vortex_mask::MaskMut;
use vortex_mask::MaskValues;

use crate::BitPackedArray;
Expand All @@ -36,10 +35,10 @@ pub(crate) const PARENT_KERNELS: ParentKernelSet<BitPackedVTable> =

/// The threshold over which it is faster to fully unpack the entire [`BitPackedArray`] and then
/// filter the result than to unpack only specific bitpacked values into the output buffer.
pub const fn unpack_then_filter_threshold<T>() -> f64 {
pub const fn unpack_then_filter_threshold(ptype: PType) -> f64 {
// TODO(connor): Where did these numbers come from? Add a public link after validating them.
// These numbers probably don't work for in-place filtering either.
match size_of::<T>() {
match ptype.byte_width() {
1 => 0.03,
2 => 0.03,
4 => 0.075,
Expand All @@ -60,7 +59,6 @@ impl ExecuteParentKernel<BitPackedVTable> for BitPackingFilterKernel {
Exact::new()
}

// TODO(joe): impl execute without to_canonical and execute_parent without vector
fn execute_parent(
&self,
array: &BitPackedArray,
Expand All @@ -70,90 +68,38 @@ impl ExecuteParentKernel<BitPackedVTable> for BitPackingFilterKernel {
) -> VortexResult<Option<Canonical>> {
let values = match parent.filter_mask() {
Mask::AllTrue(_) | Mask::AllFalse(_) => {
// No optimization for full or empty mask
return Ok(None);
}
Mask::Values(values) => values,
};

match_each_integer_ptype!(array.ptype(), |I| {
// If the density is high enough, then we would rather decompress the whole array and then apply
// a filter over decompressing values one by one.
if values.density() > unpack_then_filter_threshold::<I>() {
return Ok(None);
}
});
// If the density is high enough, then we would rather decompress the whole array and then apply
// a filter over decompressing values one by one.
if values.density() > unpack_then_filter_threshold(array.ptype()) {
return Ok(None);
}

// Filter primitive values and apply patches, returning a PrimitiveArray.
// Since FastLanes only supports unsigned types, we filter as unsigned and then
// construct the PrimitiveArray with the correct signed ptype.
let primitive = match array.ptype() {
PType::U8 => filter_and_patch::<u8>(array, values, parent)?,
PType::U16 => filter_and_patch::<u16>(array, values, parent)?,
PType::U32 => filter_and_patch::<u32>(array, values, parent)?,
PType::U64 => filter_and_patch::<u64>(array, values, parent)?,
// Since the fastlanes crate only supports unsigned integers, and since we know that all
// numbers are going to be non-negative, we can safely "cast" to unsigned and back.
PType::I8 => {
let unsigned = filter_and_patch::<u8>(array, values, parent)?;
// SAFETY: i8 and u8 have the same size and alignment.
let buffer = unsafe { unsigned.to_buffer::<u8>().transmute::<i8>() };
PrimitiveArray::new(buffer, unsigned.validity().clone())
}
PType::I16 => {
let unsigned = filter_and_patch::<u16>(array, values, parent)?;
// SAFETY: i16 and u16 have the same size and alignment.
let buffer = unsafe { unsigned.to_buffer::<u16>().transmute::<i16>() };
PrimitiveArray::new(buffer, unsigned.validity().clone())
}
PType::I32 => {
let unsigned = filter_and_patch::<u32>(array, values, parent)?;
// SAFETY: i32 and u32 have the same size and alignment.
let buffer = unsafe { unsigned.to_buffer::<u32>().transmute::<i32>() };
PrimitiveArray::new(buffer, unsigned.validity().clone())
}
PType::I64 => {
let unsigned = filter_and_patch::<u64>(array, values, parent)?;
// SAFETY: i64 and u64 have the same size and alignment.
let buffer = unsafe { unsigned.to_buffer::<u64>().transmute::<i64>() };
PrimitiveArray::new(buffer, unsigned.validity().clone())
}
other => {
unreachable!("Unsupported ptype {other} for bitpacking, we also checked this above")
}
};
// Filter and patch using the correct unsigned type for FastLanes, then cast to signed if needed.
let mut primitive = match_each_unsigned_integer_ptype!(array.ptype().to_unsigned(), |U| {
let (buffer, validity) = filter_primitive_without_patches::<U>(array, values)?;

Ok(Some(Canonical::Primitive(primitive)))
}
}
let validity = Validity::from_mask(validity, parent.dtype().nullability());
// reinterpret_cast for signed types.
PrimitiveArray::new(buffer, validity).reinterpret_cast(array.ptype())
});

/// Filters values from a BitPackedArray and applies any patches.
///
/// This helper function extracts values at the given indices, applies patches, and
/// returns the resulting PrimitiveArray.
fn filter_and_patch<U: UnsignedPType + BitPacking>(
array: &BitPackedArray,
values: &Arc<MaskValues>,
parent: &FilterArray,
) -> VortexResult<PrimitiveArray> {
let (mut buffer, mut validity) = filter_primitive_without_patches::<U>(array, values)?;

// TODO(connor): We want a `PatchesArray` or patching compute functions instead of this.
let patches = array
.patches()
.map(|patches| patches.filter(&Mask::Values(values.clone())))
.transpose()?
.flatten();
if let Some(patches) = patches {
// SAFETY: All patch indices are valid after offset adjustment (guaranteed by Patches).
// The buffer and validity have the same length.
unsafe {
patches.apply_to_buffer(buffer.as_mut_slice(), &mut validity);
let patches = array
.patches()
.map(|patches| patches.filter(&Mask::Values(values.clone())))
.transpose()?
.flatten();

if let Some(patches) = patches {
primitive = primitive.patch(&patches)?;
}
}

let validity = Validity::from_mask(validity.freeze(), parent.dtype().nullability());
Ok(PrimitiveArray::new(buffer.freeze(), validity))
Ok(Some(Canonical::Primitive(primitive)))
}
}

/// Specialized filter kernel for primitive bit-packed arrays.
Expand All @@ -170,7 +116,7 @@ fn filter_and_patch<U: UnsignedPType + BitPacking>(
fn filter_primitive_without_patches<U: UnsignedPType + BitPacking>(
array: &BitPackedArray,
selection: &Arc<MaskValues>,
) -> VortexResult<(BufferMut<U>, MaskMut)> {
) -> VortexResult<(Buffer<U>, Mask)> {
let values = filter_with_indices(array, selection.indices());
let validity = array
.validity_mask()?
Expand All @@ -183,7 +129,7 @@ fn filter_primitive_without_patches<U: UnsignedPType + BitPacking>(
"`filter_with_indices` was somehow incorrect"
);

Ok((values, validity))
Ok((values.freeze(), validity.freeze()))
}

fn filter_with_indices<T: NativePType + BitPacking>(
Expand Down
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