numkong 7.4.1

//! Owning and non-owning vector types with signed indexing and sub-byte support.
//!
//! This module provides:
//!
//! - [`Vector`]: Owning, non-resizable, SIMD-aligned vector
//! - [`VectorView`]: Immutable, strided, non-owning view
//! - [`VectorSpan`]: Mutable, strided, non-owning view
//! - [`VectorIndex`]: Signed indexing trait (negative indices wrap from end)
//!
//! All types use [`StorageElement`] as their element bound, with sub-byte types
//! (i4x2, u4x2, u1x8) supported via `try_get`/`try_set` and iterators.

extern crate alloc;

use core::marker::PhantomData;
use core::ptr::NonNull;

use crate::tensor::{Allocator, Global, Tensor, TensorError, SIMD_ALIGNMENT};
use crate::types::{DimMut, DimRef, FloatConvertible, NumberLike, StorageElement};

// region: VectorIndex — Signed Indexing

mod private {
    pub trait Sealed {}
}

/// Trait for vector index types. Supports signed integers (negative = from end).
pub trait VectorIndex: private::Sealed + Copy {
    /// Resolve this index to a `usize` offset, or `None` if out of bounds.
    fn resolve(self, len: usize) -> Option<usize>;
}

macro_rules! impl_vec_index_unsigned {
    ($($t:ty),*) => {$(
        impl private::Sealed for $t {}
        impl VectorIndex for $t {
            #[inline]
            fn resolve(self, len: usize) -> Option<usize> {
                let idx = self as usize;
                if idx < len { Some(idx) } else { None }
            }
        }
    )*};
}

macro_rules! impl_vec_index_signed {
    ($($t:ty),*) => {$(
        impl private::Sealed for $t {}
        impl VectorIndex for $t {
            #[inline]
            fn resolve(self, len: usize) -> Option<usize> {
                let idx = if self >= 0 {
                    self as usize
                } else {
                    let neg = (-(self as isize)) as usize;
                    if neg > len { return None; }
                    len - neg
                };
                if idx < len { Some(idx) } else { None }
            }
        }
    )*};
}

impl_vec_index_unsigned!(usize, u8, u16, u32, u64);
impl_vec_index_signed!(isize, i8, i16, i32, i64);

// endregion: VectorIndex

// region: Sub-byte Proxy Types

/// Immutable reference to a nibble (4-bit value) within a packed byte.
///
/// Provides unsigned (`get_unsigned`) and sign-extended (`get_signed`) access
/// to either the low or high nibble of the referenced byte.
pub struct NibbleRef<'a> {
    byte: *const u8,
    high: bool,
    _marker: PhantomData<&'a u8>,
}

impl<'a> NibbleRef<'a> {
    /// Read the nibble value as u8 (0..16).
    #[inline]
    pub fn get_unsigned(&self) -> u8 {
        // SAFETY: byte pointer is valid for the lifetime 'a
        let b = unsafe { *self.byte };
        if self.high {
            b >> 4
        } else {
            b & 0x0F
        }
    }

    /// Read the nibble value as i8 (-8..7), sign-extending bit 3.
    #[inline]
    pub fn get_signed(&self) -> i8 {
        let nibble = self.get_unsigned();
        if nibble & 0x08 != 0 {
            nibble as i8 | !0x0Fi8
        } else {
            nibble as i8
        }
    }
}

/// Mutable reference to a nibble (4-bit value) within a packed byte.
///
/// Provides read and write access to either the low or high nibble of the
/// referenced byte, preserving the other nibble on writes.
pub struct NibbleRefMut<'a> {
    byte: *mut u8,
    high: bool,
    _marker: PhantomData<&'a mut u8>,
}

impl<'a> NibbleRefMut<'a> {
    /// Read the nibble value as u8.
    #[inline]
    pub fn get_unsigned(&self) -> u8 {
        let b = unsafe { *self.byte };
        if self.high {
            b >> 4
        } else {
            b & 0x0F
        }
    }

    /// Read the nibble value as i8, sign-extending bit 3.
    #[inline]
    pub fn get_signed(&self) -> i8 {
        let nibble = self.get_unsigned();
        if nibble & 0x08 != 0 {
            nibble as i8 | !0x0Fi8
        } else {
            nibble as i8
        }
    }

    /// Set the nibble to an unsigned value (low 4 bits used).
    #[inline]
    pub fn set_unsigned(&self, val: u8) {
        // SAFETY: byte pointer is valid and mutable for the lifetime 'a
        unsafe {
            let b = *self.byte;
            if self.high {
                *self.byte = (b & 0x0F) | ((val & 0x0F) << 4);
            } else {
                *self.byte = (b & 0xF0) | (val & 0x0F);
            }
        }
    }

    /// Set the nibble to a signed value (low 4 bits used).
    #[inline]
    pub fn set_signed(&self, val: i8) { self.set_unsigned(val as u8); }
}

/// Immutable reference to a single bit within a packed byte.
///
/// The `mask` field selects which bit within the byte to read.
pub struct BitRef<'a> {
    byte: *const u8,
    mask: u8,
    _marker: PhantomData<&'a u8>,
}

impl<'a> BitRef<'a> {
    /// Read the bit as bool.
    #[inline]
    pub fn get(&self) -> bool {
        // SAFETY: byte pointer is valid for the lifetime 'a
        (unsafe { *self.byte } & self.mask) != 0
    }
}

/// Mutable reference to a single bit within a packed byte.
///
/// The `mask` field selects which bit within the byte to read or write.
/// Writes preserve all other bits in the byte.
pub struct BitRefMut<'a> {
    byte: *mut u8,
    mask: u8,
    _marker: PhantomData<&'a mut u8>,
}

impl<'a> BitRefMut<'a> {
    /// Read the bit as bool.
    #[inline]
    pub fn get(&self) -> bool {
        // SAFETY: byte pointer is valid for the lifetime 'a
        (unsafe { *self.byte } & self.mask) != 0
    }

    /// Set the bit.
    #[inline]
    pub fn set(&self, val: bool) {
        // SAFETY: byte pointer is valid and mutable for the lifetime 'a
        unsafe {
            if val {
                *self.byte |= self.mask;
            } else {
                *self.byte &= !self.mask;
            }
        }
    }
}

// endregion: Sub-byte Proxy Types

// region: Vector

/// Owning, non-resizable, SIMD-aligned vector.
///
/// Size is fixed at construction. Uses [`StorageElement`] for element types,
/// including sub-byte packed types via `T::dimensions_per_value()`.
///
/// For normal types (`dimensions_per_value() == 1`), supports `Index`/`IndexMut`.
/// For sub-byte types, use `try_get`/`try_set` or iterators.
pub struct Vector<T: StorageElement, A: Allocator = Global> {
    /// Pointer to the allocated buffer (typed as T for alignment).
    data: NonNull<T>,
    /// Number of logical dimensions.
    dims: usize,
    /// Number of storage values (dims / dimensions_per_value, rounded up).
    values: usize,
    /// Allocator instance.
    alloc: A,
}

unsafe impl<T: StorageElement + Send, A: Allocator + Send> Send for Vector<T, A> {}
unsafe impl<T: StorageElement + Sync, A: Allocator + Sync> Sync for Vector<T, A> {}

impl<T: StorageElement, A: Allocator> Drop for Vector<T, A> {
    fn drop(&mut self) {
        if self.values > 0 {
            let layout = alloc::alloc::Layout::from_size_align(
                self.values * core::mem::size_of::<T>(),
                SIMD_ALIGNMENT,
            )
            .unwrap();
            // SAFETY: data was allocated with this layout in try_zeros_in,
            // and values > 0 guarantees the pointer is non-dangling.
            unsafe {
                self.alloc.deallocate(
                    NonNull::new_unchecked(self.data.as_ptr() as *mut u8),
                    layout,
                );
            }
        }
    }
}

/// Convert dimension count to value count for type T.
///
/// For sub-byte types where `dimensions_per_value() > 1`, this performs ceiling
/// division: `(dims + dims_per_value - 1) / dims_per_value`.
#[inline]
fn dims_to_values<T: StorageElement>(dims: usize) -> usize {
    let dims_per_value = T::dimensions_per_value();
    (dims + dims_per_value - 1) / dims_per_value
}

impl<T: StorageElement, A: Allocator> Vector<T, A> {
    /// Construct a vector from raw parts, taking ownership of the allocation.
    ///
    /// # Safety
    /// - `data` must point to a valid allocation of `values * size_of::<T>()` bytes
    ///   obtained from `alloc`, aligned to [`SIMD_ALIGNMENT`].
    /// - `dims` and `values` must be consistent (`values == ceil(dims / dimensions_per_value())`).
    /// - The caller must not free the memory (this vector takes ownership).
    pub unsafe fn from_raw_parts(data: NonNull<T>, dims: usize, values: usize, alloc: A) -> Self {
        Self {
            data,
            dims,
            values,
            alloc,
        }
    }

    /// Try to create a zero-initialized vector with the given number of dimensions.
    pub fn try_zeros_in(dims: usize, alloc: A) -> Result<Self, TensorError> {
        let values = dims_to_values::<T>(dims);
        if values == 0 {
            return Ok(Self {
                data: NonNull::dangling(),
                dims: 0,
                values: 0,
                alloc,
            });
        }
        let size = values * core::mem::size_of::<T>();
        let layout = alloc::alloc::Layout::from_size_align(size, SIMD_ALIGNMENT)
            .map_err(|_| TensorError::AllocationFailed)?;
        let ptr = alloc
            .allocate(layout)
            .ok_or(TensorError::AllocationFailed)?;
        unsafe { core::ptr::write_bytes(ptr.as_ptr(), 0, size) };
        Ok(Self {
            data: unsafe { NonNull::new_unchecked(ptr.as_ptr() as *mut T) },
            dims,
            values,
            alloc,
        })
    }

    /// Try to create a vector filled with `value`.
    pub fn try_full_in(dims: usize, value: T, alloc: A) -> Result<Self, TensorError> {
        let v = Self::try_zeros_in(dims, alloc)?;
        if v.values > 0 {
            let ptr = v.data.as_ptr();
            for i in 0..v.values {
                unsafe { ptr.add(i).write(value) };
            }
        }
        Ok(v)
    }

    /// Try to create a vector filled with ones.
    pub fn try_ones_in(dims: usize, alloc: A) -> Result<Self, TensorError>
    where
        T: NumberLike,
    {
        Self::try_full_in(dims, T::one(), alloc)
    }

    /// Try to create an uninitialized vector.
    ///
    /// # Safety
    /// The returned vector's contents are uninitialized. Reading from it before
    /// writing is undefined behavior.
    pub unsafe fn try_empty_in(dims: usize, alloc: A) -> Result<Self, TensorError> {
        let values = dims_to_values::<T>(dims);
        if values == 0 {
            return Ok(Self {
                data: NonNull::dangling(),
                dims: 0,
                values: 0,
                alloc,
            });
        }
        let size = values * core::mem::size_of::<T>();
        let layout = alloc::alloc::Layout::from_size_align(size, SIMD_ALIGNMENT)
            .map_err(|_| TensorError::AllocationFailed)?;
        let ptr = alloc
            .allocate(layout)
            .ok_or(TensorError::AllocationFailed)?;
        Ok(Self {
            data: unsafe { NonNull::new_unchecked(ptr.as_ptr() as *mut T) },
            dims,
            values,
            alloc,
        })
    }

    /// Try to create a vector from a slice of scalars (f32 values).
    ///
    /// Each f32 value is converted through `DimScalar::from_f32()` before storage.
    pub fn try_from_scalars_in(scalars: &[f32], alloc: A) -> Result<Self, TensorError>
    where
        T: FloatConvertible,
    {
        let n = scalars.len();
        let mut v = Self::try_zeros_in(n, alloc)?;
        for (i, &s) in scalars.iter().enumerate() {
            v.try_set(i, T::DimScalar::from_f32(s))?;
        }
        Ok(v)
    }

    /// Try to create a vector from a slice of per-dimension scalars.
    ///
    /// Each element in `dim_values` corresponds to one logical dimension.
    pub fn try_from_dims_in(dim_values: &[T::DimScalar], alloc: A) -> Result<Self, TensorError>
    where
        T: FloatConvertible,
    {
        let n = dim_values.len();
        let mut v = Self::try_zeros_in(n, alloc)?;
        for (i, &d) in dim_values.iter().enumerate() {
            v.try_set(i, d)?;
        }
        Ok(v)
    }

    /// Number of logical dimensions.
    #[inline]
    pub fn dims(&self) -> usize { self.dims }

    /// Number of logical dimensions (same as `dims()`).
    #[inline]
    pub fn size(&self) -> usize { self.dims }

    /// Number of underlying storage values (T instances).
    #[inline]
    pub fn size_values(&self) -> usize { self.values }

    /// Returns true if the vector has zero dimensions.
    #[inline]
    pub fn is_empty(&self) -> bool { self.dims == 0 }

    /// Raw pointer to the underlying data.
    #[inline]
    pub fn as_ptr(&self) -> *const T { self.data.as_ptr() }

    /// Mutable raw pointer to the underlying data.
    #[inline]
    pub fn as_mut_ptr(&mut self) -> *mut T { self.data.as_ptr() }

    /// Size in bytes.
    #[inline]
    pub fn size_bytes(&self) -> usize { self.values * core::mem::size_of::<T>() }

    /// Create an immutable view of this vector.
    #[inline]
    pub fn view(&self) -> VectorView<'_, T> {
        VectorView {
            data: self.data.as_ptr() as *const T,
            dims: self.dims,
            stride_bytes: core::mem::size_of::<T>() as isize,
            _marker: PhantomData,
        }
    }

    /// Create a mutable span of this vector.
    #[inline]
    pub fn span(&mut self) -> VectorSpan<'_, T> {
        VectorSpan {
            data: self.data.as_ptr(),
            dims: self.dims,
            stride_bytes: core::mem::size_of::<T>() as isize,
            _marker: PhantomData,
        }
    }

    /// Try to get the logical dimension at `idx` (supports signed indexing).
    ///
    /// Returns the native `DimScalar` type (e.g., `f64` for `Vector<f64>`, `i8` for `Vector<i4x2>`).
    /// For sub-byte types, unpacks the appropriate sub-dimension from the packed storage value.
    #[inline]
    pub fn try_get<I: VectorIndex>(&self, idx: I) -> Result<T::DimScalar, TensorError>
    where
        T: FloatConvertible,
    {
        let i = idx
            .resolve(self.dims)
            .ok_or(TensorError::IndexOutOfBounds {
                index: 0,
                size: self.dims,
            })?;
        let dims_per_value = T::dimensions_per_value();
        let value_index = i / dims_per_value;
        let sub_index = i % dims_per_value;
        // SAFETY: value_index < self.values, guaranteed by dims/values invariant
        let packed = unsafe { *self.data.as_ptr().add(value_index) };
        Ok(packed.unpack().as_ref()[sub_index])
    }

    /// Try to set the logical dimension at `idx`.
    ///
    /// Accepts the native `DimScalar` type. For sub-byte types, reads the current packed value,
    /// updates the targeted sub-dimension, and writes back the modified packed value.
    #[inline]
    pub fn try_set<I: VectorIndex>(&mut self, idx: I, val: T::DimScalar) -> Result<(), TensorError>
    where
        T: FloatConvertible,
    {
        let i = idx
            .resolve(self.dims)
            .ok_or(TensorError::IndexOutOfBounds {
                index: 0,
                size: self.dims,
            })?;
        let dims_per_value = T::dimensions_per_value();
        let value_index = i / dims_per_value;
        let sub_index = i % dims_per_value;
        // SAFETY: value_index < self.values, guaranteed by dims/values invariant
        let ptr = unsafe { self.data.as_ptr().add(value_index) };
        let mut unpacked = unsafe { *ptr }.unpack();
        unpacked.as_mut()[sub_index] = val;
        unsafe { ptr.write(T::pack(unpacked)) };
        Ok(())
    }

    /// Get a slice of the underlying storage values (only for normal types).
    #[inline]
    pub fn as_slice(&self) -> &[T] {
        if T::dimensions_per_value() == 1 {
            unsafe { core::slice::from_raw_parts(self.data.as_ptr(), self.values) }
        } else {
            // For sub-byte types, return the packed values
            unsafe { core::slice::from_raw_parts(self.data.as_ptr(), self.values) }
        }
    }

    /// Get a mutable slice of the underlying storage values.
    #[inline]
    pub fn as_mut_slice(&mut self) -> &mut [T] {
        unsafe { core::slice::from_raw_parts_mut(self.data.as_ptr(), self.values) }
    }

    /// Returns an iterator over the logical dimension values, yielding [`DimRef`] proxies.
    pub fn iter(&self) -> VectorViewIterator<'_, T>
    where
        T: FloatConvertible,
    {
        self.view().iter()
    }

    /// Returns a mutable iterator over the logical dimension values, yielding [`DimMut`] proxies.
    pub fn iter_mut(&mut self) -> VectorSpanIterator<'_, T>
    where
        T: FloatConvertible,
    {
        VectorSpanIterator {
            data: self.data.as_ptr(),
            stride_bytes: core::mem::size_of::<T>() as isize,
            front: 0,
            back: self.dims,
            _marker: PhantomData,
        }
    }
}

impl<T: StorageElement, A: Allocator> Vector<T, A> {
    /// Convert this vector into a 1D tensor, transferring ownership without copying.
    pub fn try_into_tensor<const MAX_RANK: usize>(
        self,
    ) -> Result<Tensor<T, A, MAX_RANK>, TensorError> {
        if MAX_RANK == 0 {
            return Err(TensorError::TooManyRanks { got: 1 });
        }
        let mut shape = [0usize; MAX_RANK];
        shape[0] = self.dims;
        let mut strides = [0isize; MAX_RANK];
        strides[0] = core::mem::size_of::<T>() as isize;
        let alloc_bytes = self.values * core::mem::size_of::<T>();
        let data = self.data;
        // SAFETY: we read the allocator out before forget, transferring ownership
        let alloc = unsafe { core::ptr::read(&self.alloc) };
        core::mem::forget(self);
        // SAFETY: data/alloc_bytes match the original allocation
        let tensor = unsafe { Tensor::from_raw_parts(data, alloc_bytes, shape, strides, 1, alloc) };
        Ok(tensor)
    }
}

impl<T: StorageElement> Vector<T, Global> {
    /// Create a zero-initialized vector with the global allocator.
    pub fn try_zeros(dims: usize) -> Result<Self, TensorError> { Self::try_zeros_in(dims, Global) }

    /// Create a vector filled with `value`.
    pub fn try_full(dims: usize, value: T) -> Result<Self, TensorError> {
        Self::try_full_in(dims, value, Global)
    }

    /// Create a vector filled with ones.
    pub fn try_ones(dims: usize) -> Result<Self, TensorError>
    where
        T: NumberLike,
    {
        Self::try_full(dims, T::one())
    }

    /// Create an uninitialized vector.
    ///
    /// # Safety
    /// The returned vector's contents are uninitialized. Reading from it before
    /// writing is undefined behavior.
    pub unsafe fn try_empty(dims: usize) -> Result<Self, TensorError> {
        unsafe { Self::try_empty_in(dims, Global) }
    }

    /// Create a vector from scalar f32 values.
    pub fn try_from_scalars(scalars: &[f32]) -> Result<Self, TensorError>
    where
        T: FloatConvertible,
    {
        Self::try_from_scalars_in(scalars, Global)
    }

    /// Create a vector from per-dimension scalars.
    pub fn try_from_dims(dims: &[T::DimScalar]) -> Result<Self, TensorError>
    where
        T: FloatConvertible,
    {
        Self::try_from_dims_in(dims, Global)
    }
}

// Index for normal types (dimensions_per_value == 1)
impl<I: VectorIndex, T: StorageElement, A: Allocator> core::ops::Index<I> for Vector<T, A> {
    type Output = T;

    #[inline]
    fn index(&self, idx: I) -> &T {
        let i = idx.resolve(self.dims).expect("vector index out of bounds");
        debug_assert_eq!(
            T::dimensions_per_value(),
            1,
            "Index trait not supported for sub-byte types"
        );
        unsafe { &*self.data.as_ptr().add(i) }
    }
}

impl<I: VectorIndex, T: StorageElement, A: Allocator> core::ops::IndexMut<I> for Vector<T, A> {
    #[inline]
    fn index_mut(&mut self, idx: I) -> &mut T {
        let i = idx.resolve(self.dims).expect("vector index out of bounds");
        debug_assert_eq!(
            T::dimensions_per_value(),
            1,
            "IndexMut trait not supported for sub-byte types"
        );
        unsafe { &mut *self.data.as_ptr().add(i) }
    }
}

impl<T: StorageElement + Clone, A: Allocator + Clone> Vector<T, A> {
    /// Try to clone this vector, returning an error on allocation failure.
    pub fn try_clone(&self) -> Result<Self, TensorError> {
        if self.values == 0 {
            return Ok(Self {
                data: NonNull::dangling(),
                dims: 0,
                values: 0,
                alloc: self.alloc.clone(),
            });
        }
        let size = self.values * core::mem::size_of::<T>();
        let layout = alloc::alloc::Layout::from_size_align(size, SIMD_ALIGNMENT)
            .map_err(|_| TensorError::AllocationFailed)?;
        let ptr = self
            .alloc
            .allocate(layout)
            .ok_or(TensorError::AllocationFailed)?;
        unsafe {
            core::ptr::copy_nonoverlapping(self.data.as_ptr() as *const u8, ptr.as_ptr(), size);
        }
        Ok(Self {
            data: unsafe { NonNull::new_unchecked(ptr.as_ptr() as *mut T) },
            dims: self.dims,
            values: self.values,
            alloc: self.alloc.clone(),
        })
    }
}

impl<T: StorageElement + Clone, A: Allocator + Clone> Clone for Vector<T, A> {
    fn clone(&self) -> Self { self.try_clone().expect("vector clone allocation failed") }
}

impl<T: StorageElement> Default for Vector<T, Global> {
    fn default() -> Self {
        Self {
            data: NonNull::dangling(),
            dims: 0,
            values: 0,
            alloc: Global,
        }
    }
}

// endregion: Vector

// region: VectorView

/// Immutable, possibly strided, non-owning view into a vector.
pub struct VectorView<'a, T: StorageElement> {
    data: *const T,
    dims: usize,
    stride_bytes: isize,
    _marker: PhantomData<&'a T>,
}

unsafe impl<'a, T: StorageElement + Sync> Send for VectorView<'a, T> {}
unsafe impl<'a, T: StorageElement + Sync> Sync for VectorView<'a, T> {}

impl<'a, T: StorageElement> Clone for VectorView<'a, T> {
    fn clone(&self) -> Self { *self }
}
impl<'a, T: StorageElement> Copy for VectorView<'a, T> {}

impl<'a, T: StorageElement> VectorView<'a, T> {
    /// Create a view from a raw pointer, dimension count, and byte stride.
    ///
    /// # Safety
    /// - `data` must be valid for reads of `dims` elements at the given stride.
    /// - The pointed-to memory must outlive `'a`.
    /// - `stride_bytes` must be non-zero for non-empty views.
    #[inline]
    pub unsafe fn from_raw_parts(data: *const T, dims: usize, stride_bytes: isize) -> Self {
        Self {
            data,
            dims,
            stride_bytes,
            _marker: PhantomData,
        }
    }

    /// Number of logical dimensions.
    #[inline]
    pub fn dims(&self) -> usize { self.dims }

    /// Number of logical dimensions (alias for dims).
    #[inline]
    pub fn size(&self) -> usize { self.dims }

    /// Returns true if empty.
    #[inline]
    pub fn is_empty(&self) -> bool { self.dims == 0 }

    /// Stride in bytes between consecutive elements.
    #[inline]
    pub fn stride_bytes(&self) -> isize { self.stride_bytes }

    /// Returns true if elements are stored contiguously (stride == sizeof(T)).
    #[inline]
    pub fn is_contiguous(&self) -> bool { self.stride_bytes == core::mem::size_of::<T>() as isize }

    /// Get the underlying pointer.
    #[inline]
    pub fn as_ptr(&self) -> *const T { self.data }

    /// Get a contiguous slice, if this view is contiguous.
    #[inline]
    pub fn as_contiguous_slice(&self) -> Option<&'a [T]> {
        if self.is_contiguous() && T::dimensions_per_value() == 1 {
            Some(unsafe { core::slice::from_raw_parts(self.data, self.dims) })
        } else {
            None
        }
    }

    /// Try to get element at index (supports signed indexing).
    ///
    /// Returns the native `DimScalar` type. For sub-byte types, uses value_index
    /// for stride-based pointer walks to avoid buffer overread.
    #[inline]
    pub fn try_get<I: VectorIndex>(&self, idx: I) -> Result<T::DimScalar, TensorError>
    where
        T: FloatConvertible,
    {
        let i = idx
            .resolve(self.dims)
            .ok_or(TensorError::IndexOutOfBounds {
                index: 0,
                size: self.dims,
            })?;
        let dims_per_value = T::dimensions_per_value();
        let value_index = i / dims_per_value;
        let sub_index = i % dims_per_value;
        // SAFETY: stride * value_index stays within allocation
        let ptr = unsafe {
            (self.data as *const u8).offset(self.stride_bytes * value_index as isize) as *const T
        };
        Ok(unsafe { *ptr }.unpack().as_ref()[sub_index])
    }

    /// Create a reversed view by negating the stride and pointing to the last element.
    ///
    /// The returned view has the same number of dimensions but iterates in the
    /// opposite direction. For an empty view, returns a copy unchanged.
    pub fn rev(&self) -> Self {
        if self.dims == 0 {
            return *self;
        }
        let last_offset = self.stride_bytes * (self.dims as isize - 1);
        Self {
            data: unsafe { (self.data as *const u8).offset(last_offset) as *const T },
            dims: self.dims,
            stride_bytes: -self.stride_bytes,
            _marker: PhantomData,
        }
    }

    /// Create a sub-view with start, end, and step (Python-style slicing).
    ///
    /// Supports negative steps for reverse iteration. `step` must be non-zero.
    /// Returns an error if `start` or `end` exceed `dims()`, or if `step == 0`.
    pub fn try_strided(&self, start: usize, end: usize, step: isize) -> Result<Self, TensorError> {
        if start > self.dims || end > self.dims || step == 0 {
            return Err(TensorError::IndexOutOfBounds {
                index: start.max(end),
                size: self.dims,
            });
        }
        let count = if step > 0 {
            if end > start {
                (end - start + step as usize - 1) / step as usize
            } else {
                0
            }
        } else if start > end {
            let abs_step = (-step) as usize;
            (start - end + abs_step - 1) / abs_step
        } else {
            0
        };
        let new_data = unsafe {
            (self.data as *const u8).offset(self.stride_bytes * start as isize) as *const T
        };
        Ok(Self {
            data: new_data,
            dims: count,
            stride_bytes: self.stride_bytes * step,
            _marker: PhantomData,
        })
    }

    /// Returns an iterator over logical dimension values, yielding [`DimRef`] proxies.
    pub fn iter(&self) -> VectorViewIterator<'a, T>
    where
        T: FloatConvertible,
    {
        VectorViewIterator {
            data: self.data,
            stride_bytes: self.stride_bytes,
            front: 0,
            back: self.dims,
            _marker: PhantomData,
        }
    }
}

impl<'a, I: VectorIndex, T: StorageElement> core::ops::Index<I> for VectorView<'a, T> {
    type Output = T;

    #[inline]
    fn index(&self, idx: I) -> &T {
        let i = idx.resolve(self.dims).expect("view index out of bounds");
        debug_assert_eq!(
            T::dimensions_per_value(),
            1,
            "Index trait not supported for sub-byte types"
        );
        unsafe { &*((self.data as *const u8).offset(self.stride_bytes * i as isize) as *const T) }
    }
}

// endregion: VectorView

// region: VectorSpan

/// Mutable, possibly strided, non-owning view into a vector.
pub struct VectorSpan<'a, T: StorageElement> {
    data: *mut T,
    dims: usize,
    stride_bytes: isize,
    _marker: PhantomData<&'a mut T>,
}

unsafe impl<'a, T: StorageElement + Send> Send for VectorSpan<'a, T> {}
unsafe impl<'a, T: StorageElement + Sync> Sync for VectorSpan<'a, T> {}

impl<'a, T: StorageElement> VectorSpan<'a, T> {
    /// Create a mutable view from a raw pointer, dimension count, and byte stride.
    ///
    /// # Safety
    /// - `data` must be valid for reads and writes of `dims` elements at the given stride.
    /// - The pointed-to memory must outlive `'a`.
    /// - `stride_bytes` must be non-zero for non-empty views.
    /// - No other references to the memory may exist for the duration of `'a`.
    #[inline]
    pub unsafe fn from_raw_parts(data: *mut T, dims: usize, stride_bytes: isize) -> Self {
        Self {
            data,
            dims,
            stride_bytes,
            _marker: PhantomData,
        }
    }

    /// Number of logical dimensions.
    #[inline]
    pub fn dims(&self) -> usize { self.dims }

    /// Number of logical dimensions (alias for dims).
    #[inline]
    pub fn size(&self) -> usize { self.dims }

    /// Returns true if empty.
    #[inline]
    pub fn is_empty(&self) -> bool { self.dims == 0 }

    /// Stride in bytes.
    #[inline]
    pub fn stride_bytes(&self) -> isize { self.stride_bytes }

    /// Returns true if contiguous.
    #[inline]
    pub fn is_contiguous(&self) -> bool { self.stride_bytes == core::mem::size_of::<T>() as isize }

    /// Get the underlying pointer.
    #[inline]
    pub fn as_ptr(&self) -> *const T { self.data }

    /// Get the mutable underlying pointer.
    #[inline]
    pub fn as_mut_ptr(&mut self) -> *mut T { self.data }

    /// Reborrow as an immutable view, sharing the same data pointer and stride.
    pub fn as_view(&self) -> VectorView<'_, T> {
        VectorView {
            data: self.data,
            dims: self.dims,
            stride_bytes: self.stride_bytes,
            _marker: PhantomData,
        }
    }

    /// Try to get element at index.
    #[inline]
    pub fn try_get<I: VectorIndex>(&self, idx: I) -> Result<T::DimScalar, TensorError>
    where
        T: FloatConvertible,
    {
        self.as_view().try_get(idx)
    }

    /// Try to set the element at `idx`.
    ///
    /// Accepts the native `DimScalar` type. For sub-byte types, uses value_index
    /// for stride-based pointer walks to avoid buffer overwrite.
    #[inline]
    pub fn try_set<I: VectorIndex>(&mut self, idx: I, val: T::DimScalar) -> Result<(), TensorError>
    where
        T: FloatConvertible,
    {
        let i = idx
            .resolve(self.dims)
            .ok_or(TensorError::IndexOutOfBounds {
                index: 0,
                size: self.dims,
            })?;
        let dims_per_value = T::dimensions_per_value();
        let value_index = i / dims_per_value;
        let sub_index = i % dims_per_value;
        // SAFETY: stride * value_index stays within allocation
        let ptr = unsafe {
            (self.data as *mut u8).offset(self.stride_bytes * value_index as isize) as *mut T
        };
        let mut unpacked = unsafe { *ptr }.unpack();
        unpacked.as_mut()[sub_index] = val;
        unsafe { ptr.write(T::pack(unpacked)) };
        Ok(())
    }

    /// Fill all elements with a value, respecting the stride between elements.
    ///
    /// Iterates over storage values (not logical dimensions) to avoid buffer
    /// overwrite for sub-byte types.
    pub fn fill(&mut self, val: T) {
        let dims_per_value = T::dimensions_per_value();
        let values = (self.dims + dims_per_value - 1) / dims_per_value;
        for i in 0..values {
            // SAFETY: i < values; stride * i stays within the allocation
            let ptr =
                unsafe { (self.data as *mut u8).offset(self.stride_bytes * i as isize) as *mut T };
            unsafe { ptr.write(val) };
        }
    }

    /// Get a contiguous slice, if this span is contiguous.
    #[inline]
    pub fn as_contiguous_slice(&self) -> Option<&[T]> {
        if self.is_contiguous() && T::dimensions_per_value() == 1 {
            Some(unsafe { core::slice::from_raw_parts(self.data, self.dims) })
        } else {
            None
        }
    }

    /// Get a mutable contiguous slice, if this span is contiguous.
    #[inline]
    pub fn as_contiguous_slice_mut(&mut self) -> Option<&mut [T]> {
        if self.is_contiguous() && T::dimensions_per_value() == 1 {
            Some(unsafe { core::slice::from_raw_parts_mut(self.data, self.dims) })
        } else {
            None
        }
    }

    /// Returns an iterator over logical dimension values, yielding [`DimRef`] proxies.
    pub fn iter(&self) -> VectorViewIterator<'_, T>
    where
        T: FloatConvertible,
    {
        VectorViewIterator {
            data: self.data,
            stride_bytes: self.stride_bytes,
            front: 0,
            back: self.dims,
            _marker: PhantomData,
        }
    }

    /// Returns a mutable iterator over logical dimension values, yielding [`DimMut`] proxies.
    pub fn iter_mut(&mut self) -> VectorSpanIterator<'_, T>
    where
        T: FloatConvertible,
    {
        VectorSpanIterator {
            data: self.data,
            stride_bytes: self.stride_bytes,
            front: 0,
            back: self.dims,
            _marker: PhantomData,
        }
    }
}

impl<'a, I: VectorIndex, T: StorageElement> core::ops::Index<I> for VectorSpan<'a, T> {
    type Output = T;

    #[inline]
    fn index(&self, idx: I) -> &T {
        let i = idx.resolve(self.dims).expect("span index out of bounds");
        debug_assert_eq!(
            T::dimensions_per_value(),
            1,
            "Index trait not supported for sub-byte types"
        );
        unsafe { &*((self.data as *const u8).offset(self.stride_bytes * i as isize) as *const T) }
    }
}

impl<'a, I: VectorIndex, T: StorageElement> core::ops::IndexMut<I> for VectorSpan<'a, T> {
    #[inline]
    fn index_mut(&mut self, idx: I) -> &mut T {
        let i = idx.resolve(self.dims).expect("span index out of bounds");
        debug_assert_eq!(
            T::dimensions_per_value(),
            1,
            "IndexMut trait not supported for sub-byte types"
        );
        unsafe { &mut *((self.data as *mut u8).offset(self.stride_bytes * i as isize) as *mut T) }
    }
}

// endregion: VectorSpan

// region: Iterators

/// Stride-aware immutable iterator over logical dimensions, yielding [`DimRef`] proxies.
///
/// For normal types (`dimensions_per_value=1`), yields one proxy per storage value.
/// For sub-byte types, unpacks each storage value and yields sub-dimensions individually.
/// Implements `ExactSizeIterator`, `FusedIterator`, and `DoubleEndedIterator`.
pub struct VectorViewIterator<'a, T: FloatConvertible> {
    data: *const T,
    stride_bytes: isize,
    front: usize,
    back: usize,
    _marker: PhantomData<&'a T>,
}

/// Backward-compatible alias for [`VectorViewIterator`].
pub type VectorIterator<'a, T> = VectorViewIterator<'a, T>;

impl<'a, T: FloatConvertible> Iterator for VectorViewIterator<'a, T> {
    type Item = DimRef<'a, T>;

    #[inline]
    fn next(&mut self) -> Option<DimRef<'a, T>> {
        if self.front >= self.back {
            return None;
        }
        let dims_per_value = T::dimensions_per_value();
        let value_index = self.front / dims_per_value;
        let sub_index = self.front % dims_per_value;
        // SAFETY: value_index < values, stride * value_index within allocation
        let ptr = unsafe {
            (self.data as *const u8).offset(self.stride_bytes * value_index as isize) as *const T
        };
        let scalar = unsafe { *ptr }.unpack().as_ref()[sub_index];
        self.front += 1;
        Some(DimRef::new(scalar))
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let n = self.back - self.front;
        (n, Some(n))
    }
}

impl<'a, T: FloatConvertible> ExactSizeIterator for VectorViewIterator<'a, T> {}
impl<'a, T: FloatConvertible> core::iter::FusedIterator for VectorViewIterator<'a, T> {}

impl<'a, T: FloatConvertible> DoubleEndedIterator for VectorViewIterator<'a, T> {
    #[inline]
    fn next_back(&mut self) -> Option<DimRef<'a, T>> {
        if self.front >= self.back {
            return None;
        }
        self.back -= 1;
        let dims_per_value = T::dimensions_per_value();
        let value_index = self.back / dims_per_value;
        let sub_index = self.back % dims_per_value;
        let ptr = unsafe {
            (self.data as *const u8).offset(self.stride_bytes * value_index as isize) as *const T
        };
        Some(DimRef::new(unsafe { *ptr }.unpack().as_ref()[sub_index]))
    }
}

/// Stride-aware mutable iterator over logical dimensions, yielding [`DimMut`] proxies.
///
/// For normal types (`dimensions_per_value=1`), yields one proxy per storage value.
/// For sub-byte types, each proxy performs a read-modify-write on drop.
/// Implements `ExactSizeIterator`, `FusedIterator`, and `DoubleEndedIterator`.
pub struct VectorSpanIterator<'a, T: FloatConvertible> {
    data: *mut T,
    stride_bytes: isize,
    front: usize,
    back: usize,
    _marker: PhantomData<&'a mut T>,
}

impl<'a, T: FloatConvertible> Iterator for VectorSpanIterator<'a, T> {
    type Item = DimMut<'a, T>;

    #[inline]
    fn next(&mut self) -> Option<DimMut<'a, T>> {
        if self.front >= self.back {
            return None;
        }
        let dims_per_value = T::dimensions_per_value();
        let value_index = self.front / dims_per_value;
        let sub_index = self.front % dims_per_value;
        let ptr = unsafe {
            (self.data as *mut u8).offset(self.stride_bytes * value_index as isize) as *mut T
        };
        let scalar = unsafe { *ptr }.unpack().as_ref()[sub_index];
        self.front += 1;
        Some(unsafe { DimMut::new(ptr, sub_index, scalar) })
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let n = self.back - self.front;
        (n, Some(n))
    }
}

impl<'a, T: FloatConvertible> ExactSizeIterator for VectorSpanIterator<'a, T> {}
impl<'a, T: FloatConvertible> core::iter::FusedIterator for VectorSpanIterator<'a, T> {}

impl<'a, T: FloatConvertible> DoubleEndedIterator for VectorSpanIterator<'a, T> {
    #[inline]
    fn next_back(&mut self) -> Option<DimMut<'a, T>> {
        if self.front >= self.back {
            return None;
        }
        self.back -= 1;
        let dims_per_value = T::dimensions_per_value();
        let value_index = self.back / dims_per_value;
        let sub_index = self.back % dims_per_value;
        let ptr = unsafe {
            (self.data as *mut u8).offset(self.stride_bytes * value_index as isize) as *mut T
        };
        let scalar = unsafe { *ptr }.unpack().as_ref()[sub_index];
        Some(unsafe { DimMut::new(ptr, sub_index, scalar) })
    }
}

// endregion: Iterators

// region: IntoIterator (immutable)

impl<'a, T: FloatConvertible, A: Allocator> IntoIterator for &'a Vector<T, A> {
    type Item = DimRef<'a, T>;
    type IntoIter = VectorViewIterator<'a, T>;
    fn into_iter(self) -> Self::IntoIter { self.iter() }
}

impl<'a, T: FloatConvertible> IntoIterator for &'a VectorView<'a, T> {
    type Item = DimRef<'a, T>;
    type IntoIter = VectorViewIterator<'a, T>;
    fn into_iter(self) -> Self::IntoIter { self.iter() }
}

impl<'a, T: FloatConvertible> IntoIterator for &'a VectorSpan<'a, T> {
    type Item = DimRef<'a, T>;
    type IntoIter = VectorViewIterator<'a, T>;
    fn into_iter(self) -> Self::IntoIter { self.iter() }
}

// endregion: IntoIterator (immutable)

// region: IntoIterator (mutable)

impl<'a, T: FloatConvertible, A: Allocator> IntoIterator for &'a mut Vector<T, A> {
    type Item = DimMut<'a, T>;
    type IntoIter = VectorSpanIterator<'a, T>;
    fn into_iter(self) -> Self::IntoIter { self.iter_mut() }
}

impl<'a, T: FloatConvertible> IntoIterator for &'a mut VectorSpan<'a, T> {
    type Item = DimMut<'a, T>;
    type IntoIter = VectorSpanIterator<'a, T>;
    fn into_iter(self) -> Self::IntoIter { self.iter_mut() }
}

// endregion: IntoIterator (mutable)

// region: AsRef

impl<T: StorageElement, A: Allocator> AsRef<[T]> for Vector<T, A> {
    fn as_ref(&self) -> &[T] { self.as_slice() }
}

// endregion: AsRef

// region: PartialEq

impl<T: FloatConvertible, A: Allocator> PartialEq for Vector<T, A>
where
    T::DimScalar: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.dims == other.dims && self.iter().zip(other.iter()).all(|(a, b)| a == b)
    }
}

impl<T: FloatConvertible, A: Allocator> PartialEq<[T::DimScalar]> for Vector<T, A>
where
    T::DimScalar: PartialEq,
{
    fn eq(&self, other: &[T::DimScalar]) -> bool {
        self.dims == other.len() && self.iter().zip(other.iter()).all(|(a, b)| *a == *b)
    }
}

impl<'a, T: FloatConvertible> PartialEq for VectorView<'a, T>
where
    T::DimScalar: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.dims == other.dims && self.iter().zip(other.iter()).all(|(a, b)| a == b)
    }
}

impl<'a, T: FloatConvertible> PartialEq for VectorSpan<'a, T>
where
    T::DimScalar: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.dims == other.dims && self.iter().zip(other.iter()).all(|(a, b)| a == b)
    }
}

// endregion: PartialEq

// region: Tolerance Equality

impl<T: FloatConvertible, A: Allocator> Vector<T, A>
where
    T::DimScalar: NumberLike,
{
    /// Check if all elements are within tolerance of `other`.
    ///
    /// Uses the formula `|a - b| <= atol + rtol * |b|` per element.
    /// Returns `false` if dimensions differ.
    pub fn allclose<OA: Allocator>(&self, other: &Vector<T, OA>, atol: f64, rtol: f64) -> bool {
        self.dims == other.dims
            && self
                .iter()
                .zip(other.iter())
                .all(|(a, b)| crate::types::is_close(a.to_f64(), b.to_f64(), atol, rtol))
    }
}

impl<'a, T: FloatConvertible> VectorView<'a, T>
where
    T::DimScalar: NumberLike,
{
    /// Check if all elements are within tolerance of `other`.
    ///
    /// Uses the formula `|a - b| <= atol + rtol * |b|` per element.
    /// Returns `false` if dimensions differ.
    pub fn allclose(&self, other: &Self, atol: f64, rtol: f64) -> bool {
        self.dims == other.dims
            && self
                .iter()
                .zip(other.iter())
                .all(|(a, b)| crate::types::is_close(a.to_f64(), b.to_f64(), atol, rtol))
    }
}

impl<'a, T: FloatConvertible> VectorSpan<'a, T>
where
    T::DimScalar: NumberLike,
{
    /// Check if all elements are within tolerance of `other`.
    ///
    /// Uses the formula `|a - b| <= atol + rtol * |b|` per element.
    /// Returns `false` if dimensions differ.
    pub fn allclose(&self, other: &Self, atol: f64, rtol: f64) -> bool {
        self.dims == other.dims
            && self
                .iter()
                .zip(other.iter())
                .all(|(a, b)| crate::types::is_close(a.to_f64(), b.to_f64(), atol, rtol))
    }
}

// endregion: Tolerance Equality

// region: Debug and Display

/// Write a truncated, debug-formatted list from an iterator.
fn fmt_debug_list<I: Iterator>(
    f: &mut core::fmt::Formatter<'_>,
    name: &str,
    dims: usize,
    iter: I,
    limit: usize,
) -> core::fmt::Result
where
    I::Item: core::fmt::Debug,
{
    write!(f, "{}(dims={}, [", name, dims)?;
    for (i, val) in iter.enumerate() {
        if i >= limit {
            write!(f, ", ...")?;
            break;
        }
        if i > 0 {
            write!(f, ", ")?;
        }
        write!(f, "{:?}", val)?;
    }
    write!(f, "])")
}

/// Write a truncated, display-formatted list from an iterator.
fn fmt_display_list<I: Iterator>(
    f: &mut core::fmt::Formatter<'_>,
    iter: I,
    limit: usize,
) -> core::fmt::Result
where
    I::Item: core::fmt::Display,
{
    let prec = f.precision();
    write!(f, "[")?;
    for (i, val) in iter.enumerate() {
        if i >= limit {
            write!(f, ", ...")?;
            break;
        }
        if i > 0 {
            write!(f, ", ")?;
        }
        if let Some(p) = prec {
            write!(f, "{:.p$}", val)?;
        } else {
            write!(f, "{}", val)?;
        }
    }
    write!(f, "]")
}

impl<T: FloatConvertible, A: Allocator> core::fmt::Debug for Vector<T, A>
where
    T::DimScalar: core::fmt::Debug,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        fmt_debug_list(f, "Vector", self.dims, self.iter(), 8)
    }
}

impl<'a, T: FloatConvertible> core::fmt::Debug for VectorView<'a, T>
where
    T::DimScalar: core::fmt::Debug,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        fmt_debug_list(f, "VectorView", self.dims, self.iter(), 8)
    }
}

impl<'a, T: FloatConvertible> core::fmt::Debug for VectorSpan<'a, T>
where
    T::DimScalar: core::fmt::Debug,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        fmt_debug_list(f, "VectorSpan", self.dims, self.iter(), 8)
    }
}

impl<T: FloatConvertible, A: Allocator> core::fmt::Display for Vector<T, A>
where
    T::DimScalar: core::fmt::Display,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        fmt_display_list(f, self.iter(), 20)
    }
}

// endregion: Debug and Display

// region: Tests

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::{bf16, f16, i4x2, u1x8, u4x2};

    fn check_vector_roundtrip<T: FloatConvertible>() {
        let dims_per_value = T::dimensions_per_value();
        let test_dims = 16 * dims_per_value;
        let v = Vector::<T>::try_zeros(test_dims).unwrap();
        assert_eq!(v.dims(), test_dims);
        assert_eq!(v.size_values(), test_dims / dims_per_value);
        let count = v.iter().count();
        assert_eq!(count, test_dims);
    }

    fn check_vector_try_get_set<T: FloatConvertible>()
    where
        T::DimScalar: core::fmt::Debug,
    {
        let dims_per_value = T::dimensions_per_value();
        let test_dims = 4 * dims_per_value;
        let mut v = Vector::<T>::try_zeros(test_dims).unwrap();
        let one = T::DimScalar::from_f32(1.0);
        v.try_set(0_usize, one).unwrap();
        v.try_set((test_dims - 1) as i32, one).unwrap();
        let first = v.try_get(0_usize).unwrap();
        let last = v.try_get(-1_i32).unwrap();
        assert!(
            first.to_f32() >= 0.5,
            "first dim should be ~1.0, got {:?}",
            first
        );
        assert!(
            last.to_f32() >= 0.5,
            "last dim should be ~1.0, got {:?}",
            last
        );
    }

    #[test]
    fn vector_roundtrip_all_types() {
        check_vector_roundtrip::<f32>();
        check_vector_roundtrip::<f64>();
        check_vector_roundtrip::<f16>();
        check_vector_roundtrip::<bf16>();
        check_vector_roundtrip::<i4x2>();
        check_vector_roundtrip::<u4x2>();
        check_vector_roundtrip::<u1x8>();
    }

    #[test]
    fn vector_try_get_set_all_types() {
        check_vector_try_get_set::<f32>();
        check_vector_try_get_set::<f64>();
        check_vector_try_get_set::<i4x2>();
        check_vector_try_get_set::<u4x2>();
        check_vector_try_get_set::<u1x8>();
    }

    #[test]
    fn vec_index_signed() {
        let v = Vector::<f32>::try_from_dims(&[10.0, 20.0, 30.0, 40.0, 50.0]).unwrap();
        // Positive indexing
        assert_eq!(v[0], 10.0);
        assert_eq!(v[4], 50.0);
        // Negative indexing (i32 default for integer literals)
        assert_eq!(v[-1_i32], 50.0);
        assert_eq!(v[-2_i32], 40.0);
        assert_eq!(v[-5_i32], 10.0);
    }

    #[test]
    fn vector_view_stride() {
        let v = Vector::<f32>::try_from_scalars(&[1.0, 2.0, 3.0, 4.0, 5.0]).unwrap();
        let view = v.view();
        assert!(view.is_contiguous());
        assert_eq!(view.size(), 5);

        // Reversed view
        let rev = view.rev();
        assert_eq!(rev.try_get(0_usize).unwrap(), 5.0);
        assert_eq!(rev.try_get(4_usize).unwrap(), 1.0);
    }

    #[test]
    fn vector_span_fill() {
        let mut v = Vector::<f32>::try_zeros(4).unwrap();
        {
            let mut span = v.span();
            span.fill(42.0);
        }
        assert_eq!(v[0], 42.0);
        assert_eq!(v[3], 42.0);
    }

    #[test]
    fn vector_iter() {
        let v = Vector::<f32>::try_from_scalars(&[1.0, 2.0, 3.0]).unwrap();
        let vals: Vec<f32> = v.iter().map(|x| *x).collect();
        assert_eq!(vals, vec![1.0, 2.0, 3.0]);

        // Double-ended
        let rev_vals: Vec<f32> = v.iter().rev().map(|x| *x).collect();
        assert_eq!(rev_vals, vec![3.0, 2.0, 1.0]);
    }

    #[test]
    fn view_strided_iteration() {
        let v = Vector::<f32>::try_from_scalars(&[1.0, 2.0, 3.0, 4.0, 5.0]).unwrap();
        let view = v.view();

        // Every other element
        let strided = view.try_strided(0, 5, 2).unwrap();
        assert_eq!(strided.size(), 3);
        let vals: Vec<f32> = strided.iter().map(|x| *x).collect();
        assert_eq!(vals, vec![1.0, 3.0, 5.0]);
    }

    #[test]
    fn vector_filled() {
        let v = Vector::<f32>::try_full(3, 7.5).unwrap();
        assert_eq!(v[0], 7.5);
        assert_eq!(v[1], 7.5);
        assert_eq!(v[2], 7.5);
    }

    #[test]
    fn empty_vector() {
        let v = Vector::<f32>::try_zeros(0).unwrap();
        assert!(v.is_empty());
        assert_eq!(v.size(), 0);
    }

    #[test]
    #[should_panic]
    fn index_out_of_bounds() {
        let v = Vector::<f32>::try_zeros(3).unwrap();
        let _ = v[3_usize];
    }

    #[test]
    fn vector_allclose_matching() {
        let a = Vector::<f32>::try_full(4, 1.0).unwrap();
        let b = Vector::<f32>::try_full(4, 1.0 + 1e-7).unwrap();
        assert!(a.allclose(&b, 1e-6, 0.0));
    }

    #[test]
    fn vector_allclose_mismatching() {
        let a = Vector::<f32>::try_full(4, 1.0).unwrap();
        let b = Vector::<f32>::try_full(4, 2.0).unwrap();
        assert!(!a.allclose(&b, 1e-6, 0.0));
    }

    #[test]
    fn vector_allclose_different_dims() {
        let a = Vector::<f32>::try_full(3, 1.0).unwrap();
        let b = Vector::<f32>::try_full(4, 1.0).unwrap();
        assert!(!a.allclose(&b, 1e-6, 1e-6));
    }

    #[test]
    fn display_precision_forwarding() {
        let v = Vector::<f32>::try_full(3, 1.0).unwrap();
        let s = format!("{:.2}", v);
        assert_eq!(s, "[1.00, 1.00, 1.00]");
    }

    #[test]
    fn vector_span_iter_mut_f32() {
        let mut v = Vector::<f32>::try_from_scalars(&[1.0, 2.0, 3.0]).unwrap();
        for mut val in &mut v {
            *val += 10.0;
        }
        let vals: Vec<f32> = v.iter().map(|x| *x).collect();
        assert_eq!(vals, vec![11.0, 12.0, 13.0]);
    }

    #[test]
    fn vector_span_iter_mut_i4x2() {
        let mut v = Vector::<i4x2>::try_zeros(4).unwrap();
        {
            let mut span = v.span();
            for (i, mut val) in span.iter_mut().enumerate() {
                *val = (i + 1) as i8;
            }
        }
        assert_eq!(v.try_get(0_usize).unwrap(), 1);
        assert_eq!(v.try_get(1_usize).unwrap(), 2);
        assert_eq!(v.try_get(2_usize).unwrap(), 3);
        assert_eq!(v.try_get(3_usize).unwrap(), 4);
    }

    #[test]
    fn vector_span_iter_mut_u1x8() {
        let mut v = Vector::<u1x8>::try_zeros(8).unwrap();
        for (i, mut val) in v.iter_mut().enumerate() {
            if i % 2 == 0 {
                *val = 1;
            }
        }
        // Even indices should be 1, odd should be 0
        assert_eq!(v.try_get(0_usize).unwrap(), 1);
        assert_eq!(v.try_get(1_usize).unwrap(), 0);
        assert_eq!(v.try_get(2_usize).unwrap(), 1);
        assert_eq!(v.try_get(3_usize).unwrap(), 0);
    }

    #[test]
    fn vector_span_iter_double_ended() {
        let mut v = Vector::<f32>::try_from_scalars(&[1.0, 2.0, 3.0]).unwrap();
        let mut span = v.span();
        let mut it = span.iter_mut();
        // Take from front
        let mut first = it.next().unwrap();
        *first = 10.0;
        drop(first);
        // Take from back
        let mut last = it.next_back().unwrap();
        *last = 30.0;
        drop(last);
        drop(it);
        drop(span);
        assert_eq!(v.try_get(0_usize).unwrap(), 10.0);
        assert_eq!(v.try_get(1_usize).unwrap(), 2.0);
        assert_eq!(v.try_get(2_usize).unwrap(), 30.0);
    }

    #[test]
    fn vector_iterator_alias_compat() {
        // VectorIterator type alias should still work
        let v = Vector::<f32>::try_from_scalars(&[1.0]).unwrap();
        let _it: VectorIterator<'_, f32> = v.iter();
    }
}

// endregion: Tests