vortex_alp/alp/

array.rs

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright the Vortex contributors

use std::fmt::Debug;
use std::fmt::Display;
use std::fmt::Formatter;
use std::hash::Hash;
use std::hash::Hasher;

use prost::Message;
use vortex_array::Array;
use vortex_array::ArrayEq;
use vortex_array::ArrayHash;
use vortex_array::ArrayId;
use vortex_array::ArrayParts;
use vortex_array::ArrayRef;
use vortex_array::ArraySlots;
use vortex_array::ArrayView;
use vortex_array::EqMode;
use vortex_array::ExecutionCtx;
use vortex_array::ExecutionResult;
use vortex_array::IntoArray;
use vortex_array::TypedArrayRef;
use vortex_array::VortexSessionExecute;
use vortex_array::array_slots;
use vortex_array::arrays::Primitive;
use vortex_array::buffer::BufferHandle;
use vortex_array::dtype::DType;
use vortex_array::dtype::NativePType;
use vortex_array::dtype::PType;
use vortex_array::patches::PatchSlotIndices;
use vortex_array::patches::Patches;
use vortex_array::patches::PatchesData;
use vortex_array::patches::PatchesMetadata;
use vortex_array::require_child;
use vortex_array::require_patches;
use vortex_array::serde::ArrayChildren;
use vortex_array::smallvec::smallvec;
use vortex_array::vtable::VTable;
use vortex_array::vtable::ValidityChild;
use vortex_array::vtable::ValidityVTableFromChild;
use vortex_error::VortexExpect;
use vortex_error::VortexResult;
use vortex_error::vortex_bail;
use vortex_error::vortex_ensure;
use vortex_error::vortex_ensure_eq;
use vortex_error::vortex_panic;
use vortex_session::VortexSession;
use vortex_session::registry::CachedId;

use crate::ALPFloat;
use crate::alp::Exponents;
use crate::alp::decompress::execute_decompress;
use crate::alp::rules::RULES;

/// A [`ALP`]-encoded Vortex array.
pub type ALPArray = Array<ALP>;

impl ArrayHash for ALPData {
    fn array_hash<H: Hasher>(&self, state: &mut H, _accuracy: EqMode) {
        self.exponents.hash(state);
        self.patches_data.hash(state);
    }
}

impl ArrayEq for ALPData {
    fn array_eq(&self, other: &Self, _accuracy: EqMode) -> bool {
        self.exponents == other.exponents && self.patches_data == other.patches_data
    }
}

impl VTable for ALP {
    type TypedArrayData = ALPData;

    type OperationsVTable = Self;
    type ValidityVTable = ValidityVTableFromChild;

    fn id(&self) -> ArrayId {
        static ID: CachedId = CachedId::new("vortex.alp");
        *ID
    }

    fn validate(
        &self,
        data: &ALPData,
        dtype: &DType,
        len: usize,
        slots: &[Option<ArrayRef>],
    ) -> VortexResult<()> {
        let alp_slots = ALPSlotsView::from_slots(slots);
        let patches =
            PatchesData::patches_from_slots(data.patches_data.as_ref(), len, slots, PATCH_SLOTS);
        validate_parts(dtype, len, data.exponents, alp_slots.encoded, patches)
    }

    fn nbuffers(_array: ArrayView<'_, Self>) -> usize {
        0
    }

    fn buffer(_array: ArrayView<'_, Self>, idx: usize) -> BufferHandle {
        vortex_panic!("ALPArray buffer index {idx} out of bounds")
    }

    fn buffer_name(_array: ArrayView<'_, Self>, _idx: usize) -> Option<String> {
        None
    }

    fn with_buffers(
        &self,
        array: ArrayView<'_, Self>,
        buffers: &[BufferHandle],
    ) -> VortexResult<ArrayParts<Self>> {
        vortex_array::vtable::with_empty_buffers(self, array, buffers)
    }

    fn serialize(
        array: ArrayView<'_, Self>,
        _session: &VortexSession,
    ) -> VortexResult<Option<Vec<u8>>> {
        let exponents = array.exponents();
        Ok(Some(
            ALPMetadata {
                exp_e: exponents.e as u32,
                exp_f: exponents.f as u32,
                patches: array
                    .patches()
                    .map(|p| p.to_metadata(array.len(), array.dtype()))
                    .transpose()?,
            }
            .encode_to_vec(),
        ))
    }

    fn deserialize(
        &self,
        dtype: &DType,
        len: usize,
        metadata: &[u8],
        _buffers: &[BufferHandle],
        children: &dyn ArrayChildren,
        session: &VortexSession,
    ) -> VortexResult<ArrayParts<Self>> {
        let metadata = ALPMetadata::decode(metadata)?;
        let encoded_ptype = match &dtype {
            DType::Primitive(PType::F32, n) => DType::Primitive(PType::I32, *n),
            DType::Primitive(PType::F64, n) => DType::Primitive(PType::I64, *n),
            d => vortex_bail!(MismatchedTypes: "f32 or f64", d),
        };
        let encoded = children.get(0, &encoded_ptype, len)?;

        let patches = metadata
            .patches
            .map(|p| {
                let indices = children.get(1, &p.indices_dtype()?, p.len()?)?;
                let values = children.get(2, dtype, p.len()?)?;
                let chunk_offsets = p
                    .chunk_offsets_dtype()?
                    .map(|dtype| children.get(3, &dtype, usize::try_from(p.chunk_offsets_len())?))
                    .transpose()?;

                Patches::new(
                    len,
                    p.offset()?,
                    indices,
                    values,
                    chunk_offsets,
                    &mut session.create_execution_ctx(),
                )
            })
            .transpose()?;

        let slots = ALPData::make_slots(&encoded, patches.as_ref());
        let data = ALPData::new(
            Exponents {
                e: u8::try_from(metadata.exp_e)?,
                f: u8::try_from(metadata.exp_f)?,
            },
            patches,
        );
        Ok(ArrayParts::new(
            self.clone(),
            dtype.clone(),
            len,
            data,
            slots,
        ))
    }

    fn slot_name(_array: ArrayView<'_, Self>, idx: usize) -> String {
        ALPSlots::NAMES[idx].to_string()
    }

    fn execute(array: Array<Self>, ctx: &mut ExecutionCtx) -> VortexResult<ExecutionResult> {
        let array = require_child!(array, array.encoded(), ALPSlots::ENCODED => Primitive);
        require_patches!(
            array,
            ALPSlots::PATCH_INDICES,
            ALPSlots::PATCH_VALUES,
            ALPSlots::PATCH_CHUNK_OFFSETS
        );

        Ok(ExecutionResult::done(
            execute_decompress(array, ctx)?.into_array(),
        ))
    }

    fn reduce_parent(
        array: ArrayView<'_, Self>,
        parent: &ArrayRef,
        child_idx: usize,
    ) -> VortexResult<Option<ArrayRef>> {
        RULES.evaluate(array, parent, child_idx)
    }
}

#[array_slots(ALP)]
pub struct ALPSlots {
    /// The ALP-encoded values array.
    #[slot(0)]
    pub encoded: ArrayRef,
    /// The indices of exception values that could not be ALP-encoded.
    #[slot(1)]
    pub patch_indices: Option<ArrayRef>,
    /// The exception values that could not be ALP-encoded.
    #[slot(2)]
    pub patch_values: Option<ArrayRef>,
    /// Chunk offsets for the patch indices/values.
    #[slot(3)]
    pub patch_chunk_offsets: Option<ArrayRef>,
}

const PATCH_SLOTS: PatchSlotIndices = PatchSlotIndices {
    indices: ALPSlots::PATCH_INDICES,
    values: ALPSlots::PATCH_VALUES,
    chunk_offsets: ALPSlots::PATCH_CHUNK_OFFSETS,
};

#[derive(Clone, Debug)]
pub struct ALPData {
    patches_data: Option<PatchesData>,
    exponents: Exponents,
}

impl Display for ALPData {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        write!(f, "exponents: {}", self.exponents)?;
        if let Some(pd) = &self.patches_data {
            write!(f, ", patch_offset: {}", pd.offset())?;
        }
        Ok(())
    }
}

#[derive(Clone, Debug)]
pub struct ALP;

#[derive(Clone, prost::Message)]
pub struct ALPMetadata {
    #[prost(uint32, tag = "1")]
    pub(crate) exp_e: u32,
    #[prost(uint32, tag = "2")]
    pub(crate) exp_f: u32,
    #[prost(message, optional, tag = "3")]
    pub(crate) patches: Option<PatchesMetadata>,
}

impl ALPData {
    fn validate_components(
        encoded: &ArrayRef,
        exponents: Exponents,
        patches: Option<&Patches>,
    ) -> VortexResult<()> {
        vortex_ensure!(
            matches!(
                encoded.dtype(),
                DType::Primitive(PType::I32 | PType::I64, _)
            ),
            "ALP encoded ints have invalid DType {}",
            encoded.dtype(),
        );

        // Validate exponents are in-bounds for the float, and that patches have the proper
        // length and type.
        let Exponents { e, f } = exponents;
        match encoded.dtype().as_ptype() {
            PType::I32 => {
                vortex_ensure!(exponents.e <= f32::MAX_EXPONENT, "e out of bounds: {e}");
                vortex_ensure!(exponents.f <= f32::MAX_EXPONENT, "f out of bounds: {f}");
                if let Some(patches) = patches {
                    Self::validate_patches::<f32>(patches, encoded)?;
                }
            }
            PType::I64 => {
                vortex_ensure!(e <= f64::MAX_EXPONENT, "e out of bounds: {e}");
                vortex_ensure!(f <= f64::MAX_EXPONENT, "f out of bounds: {f}");

                if let Some(patches) = patches {
                    Self::validate_patches::<f64>(patches, encoded)?;
                }
            }
            _ => unreachable!(),
        }

        // Validate patches
        if let Some(patches) = patches {
            vortex_ensure_eq!(patches.array_len(), encoded.len());

            // Verify that the patches DType are of the proper DType.
        }

        Ok(())
    }

    fn logical_dtype(encoded: &ArrayRef) -> VortexResult<DType> {
        match encoded.dtype() {
            DType::Primitive(PType::I32, nullability) => {
                Ok(DType::Primitive(PType::F32, *nullability))
            }
            DType::Primitive(PType::I64, nullability) => {
                Ok(DType::Primitive(PType::F64, *nullability))
            }
            _ => vortex_bail!("ALP encoded ints have invalid DType {}", encoded.dtype(),),
        }
    }

    /// Validate that any patches provided are valid for the ALPArray.
    fn validate_patches<T: ALPFloat + NativePType>(
        patches: &Patches,
        encoded: &ArrayRef,
    ) -> VortexResult<()> {
        vortex_ensure_eq!(patches.array_len(), encoded.len());

        let expected_type = DType::Primitive(T::PTYPE, encoded.dtype().nullability());
        vortex_ensure_eq!(patches.dtype(), &expected_type);

        Ok(())
    }
}

impl ALPData {
    /// Build a new `ALPArray` from components, panicking on validation failure.
    ///
    /// See [`ALP::try_new`] for reference on preconditions that must pass before
    /// calling this method.
    pub fn new(exponents: Exponents, patches: Option<Patches>) -> Self {
        Self {
            patches_data: patches.as_ref().map(PatchesData::from_patches),
            exponents,
        }
    }

    /// Build a new `ALPArray` from components:
    ///
    /// * `encoded` contains the ALP-encoded ints. Any null values are replaced with placeholders
    /// * `exponents` are the ALP exponents, valid range depends on the data type
    /// * `patches` are any patch values that don't cleanly encode using the ALP conversion function
    ///
    /// Build a new `ALPArray` from components without validation.
    ///
    /// See [`ALP::try_new`] for information about the preconditions that should be checked
    /// **before** calling this method.
    pub(crate) unsafe fn new_unchecked(exponents: Exponents, patches: Option<Patches>) -> Self {
        Self::new(exponents, patches)
    }
}

/// Constructors for [`ALPArray`].
impl ALP {
    pub fn new(encoded: ArrayRef, exponents: Exponents, patches: Option<Patches>) -> ALPArray {
        let dtype = ALPData::logical_dtype(&encoded).vortex_expect("ALP encoded dtype");
        let len = encoded.len();
        let slots = ALPData::make_slots(&encoded, patches.as_ref());
        unsafe {
            Array::from_parts_unchecked(ArrayParts::new(
                ALP,
                dtype,
                len,
                ALPData::new(exponents, patches),
                slots,
            ))
        }
    }

    pub fn try_new(
        encoded: ArrayRef,
        exponents: Exponents,
        patches: Option<Patches>,
    ) -> VortexResult<ALPArray> {
        let dtype = ALPData::logical_dtype(&encoded)?;
        let len = encoded.len();
        let slots = ALPData::make_slots(&encoded, patches.as_ref());
        let data = ALPData::new(exponents, patches);
        Array::try_from_parts(ArrayParts::new(ALP, dtype, len, data, slots))
    }

    /// # Safety
    /// See [`ALP::try_new`] for preconditions.
    pub unsafe fn new_unchecked(
        encoded: ArrayRef,
        exponents: Exponents,
        patches: Option<Patches>,
    ) -> ALPArray {
        let dtype = ALPData::logical_dtype(&encoded).vortex_expect("ALP encoded dtype");
        let len = encoded.len();
        let slots = ALPData::make_slots(&encoded, patches.as_ref());
        let data = unsafe { ALPData::new_unchecked(exponents, patches) };
        unsafe { Array::from_parts_unchecked(ArrayParts::new(ALP, dtype, len, data, slots)) }
    }
}

impl ALPData {
    fn make_slots(encoded: &ArrayRef, patches: Option<&Patches>) -> ArraySlots {
        let mut slots: ArraySlots = smallvec![Some(encoded.clone())];
        PatchesData::push_slots(&mut slots, patches);
        slots
    }

    #[inline]
    pub fn exponents(&self) -> Exponents {
        self.exponents
    }
}

pub trait ALPArrayExt: ALPArraySlotsExt {
    fn exponents(&self) -> Exponents {
        self.exponents
    }

    fn patches(&self) -> Option<Patches> {
        PatchesData::patches_from_slots(
            self.patches_data.as_ref(),
            self.len(),
            self.slots(),
            PATCH_SLOTS,
        )
    }
}

fn validate_parts(
    dtype: &DType,
    len: usize,
    exponents: Exponents,
    encoded: &ArrayRef,
    patches: Option<Patches>,
) -> VortexResult<()> {
    let logical_dtype = ALPData::logical_dtype(encoded)?;
    ALPData::validate_components(encoded, exponents, patches.as_ref())?;
    vortex_ensure_eq!(encoded.len(), len, "ALP encoded len must match outer len");
    vortex_ensure_eq!(
        &logical_dtype,
        dtype,
        "ALP dtype does not match encoded logical dtype"
    );
    Ok(())
}

impl<T: TypedArrayRef<ALP>> ALPArrayExt for T {}

pub trait ALPArrayOwnedExt {
    fn into_parts(self) -> (ArrayRef, Exponents, Option<Patches>);
}

impl ALPArrayOwnedExt for Array<ALP> {
    #[inline]
    fn into_parts(self) -> (ArrayRef, Exponents, Option<Patches>) {
        let patches = self.patches();
        let exponents = self.exponents();
        let encoded = self.encoded().clone();
        (encoded, exponents, patches)
    }
}

impl ValidityChild<ALP> for ALP {
    fn validity_child(array: ArrayView<'_, ALP>) -> ArrayRef {
        array.encoded().clone()
    }
}

#[cfg(test)]
mod tests {
    use std::f64::consts::PI;
    use std::sync::LazyLock;

    use rstest::rstest;
    use vortex_array::VortexSessionExecute;
    use vortex_array::arrays::PrimitiveArray;
    use vortex_array::assert_arrays_eq;
    use vortex_session::VortexSession;

    use super::*;
    use crate::alp_encode;
    use crate::decompress_into_array;

    static SESSION: LazyLock<VortexSession> = LazyLock::new(|| {
        let session = vortex_array::array_session();
        crate::initialize(&session);
        session
    });

    #[rstest]
    #[case(0)]
    #[case(1)]
    #[case(100)]
    #[case(1023)]
    #[case(1024)]
    #[case(1025)]
    #[case(2047)]
    #[case(2048)]
    #[case(2049)]
    fn test_execute_f32(#[case] size: usize) {
        let mut ctx = SESSION.create_execution_ctx();
        let values = PrimitiveArray::from_iter((0..size).map(|i| i as f32));
        let encoded = alp_encode(values.as_view(), None, &mut ctx).unwrap();

        // Compare against the traditional array-based decompress path
        let expected =
            decompress_into_array(encoded.clone(), &mut SESSION.create_execution_ctx()).unwrap();

        assert_arrays_eq!(expected, values, &mut ctx);
        assert_arrays_eq!(encoded, values, &mut ctx);
    }

    #[rstest]
    #[case(0)]
    #[case(1)]
    #[case(100)]
    #[case(1023)]
    #[case(1024)]
    #[case(1025)]
    #[case(2047)]
    #[case(2048)]
    #[case(2049)]
    fn test_execute_f64(#[case] size: usize) {
        let values = PrimitiveArray::from_iter((0..size).map(|i| i as f64));
        let encoded =
            alp_encode(values.as_view(), None, &mut SESSION.create_execution_ctx()).unwrap();

        let mut ctx = SESSION.create_execution_ctx();
        // Compare against the traditional array-based decompress path
        let expected =
            decompress_into_array(encoded.clone(), &mut SESSION.create_execution_ctx()).unwrap();

        assert_arrays_eq!(expected, values, &mut ctx);
        assert_arrays_eq!(encoded, values, &mut ctx);
    }

    #[rstest]
    #[case(100)]
    #[case(1023)]
    #[case(1024)]
    #[case(1025)]
    #[case(2047)]
    #[case(2048)]
    #[case(2049)]
    fn test_execute_with_patches(#[case] size: usize) {
        let values: Vec<f64> = (0..size)
            .map(|i| match i % 4 {
                0..=2 => 1.0,
                _ => PI,
            })
            .collect();

        let array = PrimitiveArray::from_iter(values);
        let encoded =
            alp_encode(array.as_view(), None, &mut SESSION.create_execution_ctx()).unwrap();
        assert!(encoded.patches().unwrap().array_len() > 0);

        let mut ctx = SESSION.create_execution_ctx();
        // Compare against the traditional array-based decompress path
        let expected =
            decompress_into_array(encoded.clone(), &mut SESSION.create_execution_ctx()).unwrap();

        assert_arrays_eq!(expected, array, &mut ctx);
        assert_arrays_eq!(encoded, array, &mut ctx);
    }

    #[rstest]
    #[case(0)]
    #[case(1)]
    #[case(100)]
    #[case(1023)]
    #[case(1024)]
    #[case(1025)]
    #[case(2047)]
    #[case(2048)]
    #[case(2049)]
    fn test_execute_with_validity(#[case] size: usize) {
        let values: Vec<Option<f32>> = (0..size)
            .map(|i| if i % 2 == 1 { None } else { Some(1.0) })
            .collect();

        let array = PrimitiveArray::from_option_iter(values);
        let encoded =
            alp_encode(array.as_view(), None, &mut SESSION.create_execution_ctx()).unwrap();

        let mut ctx = SESSION.create_execution_ctx();
        // Compare against the traditional array-based decompress path
        let expected =
            decompress_into_array(encoded.clone(), &mut SESSION.create_execution_ctx()).unwrap();

        assert_arrays_eq!(expected, array, &mut ctx);
        assert_arrays_eq!(encoded, array, &mut ctx);
    }

    #[rstest]
    #[case(100)]
    #[case(1023)]
    #[case(1024)]
    #[case(1025)]
    #[case(2047)]
    #[case(2048)]
    #[case(2049)]
    fn test_execute_with_patches_and_validity(#[case] size: usize) {
        let values: Vec<Option<f64>> = (0..size)
            .map(|idx| match idx % 3 {
                0 => Some(1.0),
                1 => None,
                _ => Some(PI),
            })
            .collect();

        let array = PrimitiveArray::from_option_iter(values);
        let encoded =
            alp_encode(array.as_view(), None, &mut SESSION.create_execution_ctx()).unwrap();
        assert!(encoded.patches().unwrap().array_len() > 0);

        let mut ctx = SESSION.create_execution_ctx();
        // Compare against the traditional array-based decompress path
        let expected =
            decompress_into_array(encoded.clone(), &mut SESSION.create_execution_ctx()).unwrap();

        assert_arrays_eq!(expected, array, &mut ctx);
        assert_arrays_eq!(encoded, array, &mut ctx);
    }

    #[rstest]
    #[case(500, 100)]
    #[case(1000, 200)]
    #[case(2048, 512)]
    fn test_execute_sliced_vector(#[case] size: usize, #[case] slice_start: usize) {
        let values: Vec<Option<f64>> = (0..size)
            .map(|i| {
                if i % 5 == 0 {
                    None
                } else if i % 4 == 3 {
                    Some(PI)
                } else {
                    Some(1.0)
                }
            })
            .collect();

        let mut ctx = SESSION.create_execution_ctx();
        let array = PrimitiveArray::from_option_iter(values.clone());
        let encoded = alp_encode(array.as_view(), None, &mut ctx).unwrap();

        let slice_end = size - slice_start;
        let sliced_encoded = encoded.slice(slice_start..slice_end).unwrap();

        let expected =
            PrimitiveArray::from_option_iter(values[slice_start..slice_end].iter().copied());
        assert_arrays_eq!(sliced_encoded, expected, &mut ctx);
    }

    #[rstest]
    #[case(500, 100)]
    #[case(1000, 200)]
    #[case(2048, 512)]
    fn test_sliced_to_primitive(#[case] size: usize, #[case] slice_start: usize) {
        let mut ctx = SESSION.create_execution_ctx();
        let values: Vec<Option<f64>> = (0..size)
            .map(|i| {
                if i % 5 == 0 {
                    None
                } else if i % 4 == 3 {
                    Some(PI)
                } else {
                    Some(1.0)
                }
            })
            .collect();

        let array = PrimitiveArray::from_option_iter(values.clone());
        let encoded = alp_encode(array.as_view(), None, &mut ctx).unwrap();

        let slice_end = size - slice_start;
        let sliced_encoded = encoded.slice(slice_start..slice_end).unwrap();

        let expected =
            PrimitiveArray::from_option_iter(values[slice_start..slice_end].iter().copied());
        assert_arrays_eq!(sliced_encoded, expected, &mut ctx);
    }

    /// Regression test for issue #5948: execute_decompress drops patches when chunk_offsets is
    /// None.
    ///
    /// When patches exist but do NOT have chunk_offsets, the execute path incorrectly passes
    /// `None` to `decompress_unchunked_core` instead of the actual patches.
    ///
    /// This can happen after file IO serialization/deserialization where chunk_offsets may not
    /// be preserved, or when building ALPArrays manually without chunk_offsets.
    #[test]
    fn test_execute_decompress_with_patches_no_chunk_offsets_regression_5948() {
        let mut ctx = SESSION.create_execution_ctx();
        // Create an array with values that will produce patches. PI doesn't encode cleanly.
        let values: Vec<f64> = vec![1.0, 2.0, PI, 4.0, 5.0];
        let original = PrimitiveArray::from_iter(values);

        // First encode normally to get a properly formed ALPArray with patches.
        let normally_encoded = alp_encode(
            original.as_view(),
            None,
            &mut SESSION.create_execution_ctx(),
        )
        .unwrap();
        assert!(
            normally_encoded.patches().is_some(),
            "Test requires patches to be present"
        );

        let original_patches = normally_encoded.patches().unwrap();
        assert!(
            original_patches.chunk_offsets().is_some(),
            "Normal encoding should have chunk_offsets"
        );

        // Rebuild the patches WITHOUT chunk_offsets to simulate deserialized patches.
        let patches_without_chunk_offsets = Patches::new(
            original_patches.array_len(),
            original_patches.offset(),
            original_patches.indices().clone(),
            original_patches.values().clone(),
            None, // NO chunk_offsets - this triggers the bug!
            &mut ctx,
        )
        .unwrap();

        // Build a new ALPArray with the same encoded data but patches without chunk_offsets.
        let alp_without_chunk_offsets = ALP::new(
            normally_encoded.encoded().clone(),
            normally_encoded.exponents(),
            Some(patches_without_chunk_offsets),
        );

        // The legacy decompress_into_array path should work correctly.
        let result_legacy = decompress_into_array(
            alp_without_chunk_offsets.clone(),
            &mut SESSION.create_execution_ctx(),
        )
        .unwrap();
        let legacy_slice = result_legacy.as_slice::<f64>();

        // Verify the legacy path produces correct values.
        assert!(
            (legacy_slice[2] - PI).abs() < 1e-10,
            "Legacy path should have PI at index 2, got {}",
            legacy_slice[2]
        );

        // The execute path has the bug - it drops patches when chunk_offsets is None.
        let result_execute = { execute_decompress(alp_without_chunk_offsets, &mut ctx).unwrap() };
        let execute_slice = result_execute.as_slice::<f64>();

        // This assertion FAILS until the bug is fixed because execute_decompress drops patches.
        assert!(
            (execute_slice[2] - PI).abs() < 1e-10,
            "Execute path should have PI at index 2, but got {} (patches were dropped!)",
            execute_slice[2]
        );
    }
}