strided-basic 0.4.2

//! Prepared (compile-once, execute-many) copy plans over raw strided layouts.
//!
//! [`copy_scale_raw`](crate::copy_scale_raw) and friends rebuild the fused
//! loop nest on every call; for prepared-replay consumers that issue many
//! small copies with a fixed layout, that per-call planning dominates
//! (see issue #139). [`CopyPlan`] splits the work: [`CopyPlan::compile`]
//! validates the layout pair and builds the fused traversal once,
//! [`CopyPlan::execute`]/[`CopyPlan::execute_scale`]/[`CopyPlan::execute_conj`]
//! replay it with no planning and no heap allocation for ranks at most
//! [`RAW_FUSED_RANK_LIMIT`](crate::RAW_FUSED_RANK_LIMIT).

use core::{
    marker::PhantomData,
    mem::MaybeUninit,
    ops::{Add, Mul},
};

use crate::map_view::map_raw_into;
use crate::ops_view::{copy_conj, copy_into, copy_scale};
use crate::raw_ops::{apply_fused_pair, fuse_pair_layout, FusedPairLayout};
use crate::{
    ElementOpApply, Identity, MaybeSendSync, RawStridedMut, RawStridedRef, Result, StridedError,
};

// Same pattern as map_view.rs / outer_product.rs: stack storage when the
// parallel feature pulls in smallvec, plain Vec otherwise. Only `compile`
// touches these; `execute*` never allocates either way.
#[cfg(feature = "parallel")]
type AxisVec<T> = smallvec::SmallVec<[T; crate::RAW_FUSED_RANK_LIMIT]>;
#[cfg(not(feature = "parallel"))]
type AxisVec<T> = Vec<T>;

pub(crate) trait OverwriteWriter<T> {
    fn dims(&self) -> &[usize];
    fn strides(&self) -> &[isize];
    fn offset(&self) -> isize;
    /// # Safety
    /// The caller must use the pointer only for the validated allocation and
    /// logical layout represented by this writer.
    unsafe fn data_ptr(&mut self) -> *mut T;
    /// # Safety
    /// The offset must be an in-bounds logical destination proven by layout.
    unsafe fn write_at(&mut self, offset: isize, value: T);
}

pub(crate) trait ReadModifyWrite<T>: OverwriteWriter<T> {
    /// # Safety
    /// The offset must be an in-bounds initialized slot covered by the
    /// traversal's copy and disjointness proof.
    unsafe fn add_at<F>(&mut self, offset: isize, value: T, combine: F)
    where
        F: FnOnce(T, T) -> T;
}

impl<'a, T> OverwriteWriter<T> for RawStridedMut<'a, T> {
    fn dims(&self) -> &[usize] {
        self.dims()
    }
    fn strides(&self) -> &[isize] {
        self.strides()
    }
    fn offset(&self) -> isize {
        self.offset()
    }
    unsafe fn data_ptr(&mut self) -> *mut T {
        self.data_mut().as_mut_ptr()
    }
    unsafe fn write_at(&mut self, offset: isize, value: T) {
        // SAFETY: the prepared layout validates every logical destination.
        unsafe { self.data_mut().as_mut_ptr().offset(offset).write(value) }
    }
}

impl<'a, T> ReadModifyWrite<T> for RawStridedMut<'a, T>
where
    T: Add<Output = T>,
{
    #[inline(always)]
    unsafe fn add_at<F>(&mut self, offset: isize, value: T, combine: F)
    where
        F: FnOnce(T, T) -> T,
    {
        // SAFETY: the copy or initialized caller proves this logical slot.
        unsafe {
            let ptr = self.data_mut().as_mut_ptr().offset(offset);
            ptr.write(combine(ptr.read(), value));
        }
    }
}

impl<'a, T> OverwriteWriter<T> for RawStridedMut<'a, MaybeUninit<T>> {
    fn dims(&self) -> &[usize] {
        self.dims()
    }
    fn strides(&self) -> &[isize] {
        self.strides()
    }
    fn offset(&self) -> isize {
        self.offset()
    }
    unsafe fn data_ptr(&mut self) -> *mut T {
        self.data_mut().as_mut_ptr().cast()
    }
    unsafe fn write_at(&mut self, offset: isize, value: T) {
        // SAFETY: the prepared layout validates every logical destination.
        unsafe {
            self.data_mut()
                .as_mut_ptr()
                .offset(offset)
                .write(MaybeUninit::new(value))
        }
    }
}

pub(crate) struct InitializedRawDest<'a, T> {
    ptr: *mut T,
    extent: usize,
    dims: &'a [usize],
    strides: &'a [isize],
    offset: isize,
    _marker: PhantomData<&'a mut [MaybeUninit<T>]>,
}

impl<'a, T> OverwriteWriter<T> for InitializedRawDest<'a, T> {
    fn dims(&self) -> &[usize] {
        self.dims
    }
    fn strides(&self) -> &[isize] {
        self.strides
    }
    fn offset(&self) -> isize {
        self.offset
    }
    unsafe fn data_ptr(&mut self) -> *mut T {
        self.ptr
    }
    unsafe fn write_at(&mut self, offset: isize, value: T) {
        debug_assert!(offset >= 0 && (offset as usize) < self.extent);
        // SAFETY: the copy proof and extent check cover this logical slot.
        unsafe { self.ptr.offset(offset).write(value) }
    }
}

impl<'a, T> ReadModifyWrite<T> for InitializedRawDest<'a, T>
where
    T: Add<Output = T>,
{
    #[inline(always)]
    unsafe fn add_at<F>(&mut self, offset: isize, value: T, combine: F)
    where
        F: FnOnce(T, T) -> T,
    {
        debug_assert!(offset >= 0 && (offset as usize) < self.extent);
        // SAFETY: the copy proof and extent check cover this logical slot.
        unsafe {
            let ptr = self.ptr.offset(offset);
            ptr.write(combine(ptr.read(), value));
        }
    }
}

/// A compiled copy traversal for one `(dims, dst_strides, src_strides)`
/// layout pair.
///
/// `compile` proves the layout facts once (rank agreement, extent overflow,
/// destination injectivity) and fuses/orders the loop nest; each `execute*`
/// call then only re-checks the per-call facts (that the supplied views carry
/// exactly the compiled layout) before replaying the prepared loops.
///
/// Overlapping `src`/`dest` memory is not supported, matching the rest of the
/// crate.
///
/// Ranks above [`RAW_FUSED_RANK_LIMIT`](crate::RAW_FUSED_RANK_LIMIT) are supported through the view-based
/// kernels; only that fallback path may allocate.
///
/// # Example
///
/// ```rust
/// use strided_basic::{CopyPlan, RawStridedMut, RawStridedRef};
///
/// let dims = [2usize, 3];
/// let src_strides = [3isize, 1];
/// let dst_strides = [1isize, 2]; // transposed destination
/// let plan = CopyPlan::compile(&dims, &dst_strides, &src_strides).unwrap();
///
/// let src = [0.0f64, 1.0, 2.0, 10.0, 11.0, 12.0];
/// let mut dst = [0.0f64; 6];
/// let src_ref = RawStridedRef::new(&src, &dims, &src_strides, 0).unwrap();
/// let mut dst_mut = RawStridedMut::new(&mut dst, &dims, &dst_strides, 0).unwrap();
/// plan.execute(&mut dst_mut, &src_ref).unwrap();
/// assert_eq!(dst, [0.0, 10.0, 1.0, 11.0, 2.0, 12.0]);
/// ```
#[derive(Clone, Debug)]
pub struct CopyPlan {
    dims: AxisVec<usize>,
    dst_strides: AxisVec<isize>,
    src_strides: AxisVec<isize>,
    /// `None` when rank exceeds [`RAW_FUSED_RANK_LIMIT`](crate::RAW_FUSED_RANK_LIMIT); `execute*` then
    /// falls back to the view-based kernels.
    fused: Option<FusedPairLayout>,
}

impl CopyPlan {
    pub(crate) fn execute_uninit_then<'a, T, R>(
        &self,
        dest: &'a mut RawStridedMut<'a, MaybeUninit<T>>,
        src: &RawStridedRef<'_, T>,
        f: impl for<'b> FnOnce(InitializedRawDest<'b, T>) -> R,
    ) -> Result<R>
    where
        T: Copy + MaybeSendSync,
    {
        self.execute_uninit(dest, src)?;
        let data = dest.data_mut();
        let receipt = InitializedRawDest {
            ptr: data.as_mut_ptr().cast(),
            extent: data.len(),
            dims: dest.dims(),
            strides: dest.strides(),
            offset: dest.offset(),
            _marker: PhantomData,
        };
        Ok(f(receipt))
    }

    /// Compile a copy plan for the given layout pair.
    ///
    /// Performs the layout validation and traversal construction
    /// (fuse + order) once:
    ///
    /// - `dims`, `dst_strides`, and `src_strides` must have equal length
    ///   ([`StridedError::StrideLengthMismatch`]);
    /// - the total element count must not overflow `usize`
    ///   ([`StridedError::OffsetOverflow`]);
    /// - the destination layout must be injective, i.e. map distinct logical
    ///   indices to distinct offsets
    ///   ([`StridedError::NonInjectiveOutputLayout`]).
    pub fn compile(dims: &[usize], dst_strides: &[isize], src_strides: &[isize]) -> Result<Self> {
        if dims.len() != dst_strides.len() || dims.len() != src_strides.len() {
            return Err(StridedError::StrideLengthMismatch);
        }
        // A zero-sized layout has zero elements even when its other extents
        // overflow; only a nonempty overflowing count is rejected.
        crate::kernel::total_len(dims)?;
        if !crate::layout_check::is_injective_layout(dims, dst_strides) {
            return Err(StridedError::NonInjectiveOutputLayout);
        }
        Ok(Self {
            dims: dims.into(),
            dst_strides: dst_strides.into(),
            src_strides: src_strides.into(),
            fused: fuse_pair_layout(dims, dst_strides, src_strides),
        })
    }

    /// Check the per-call facts: the supplied views must carry exactly the
    /// compiled layout. Buffer bounds against that layout were already proven
    /// by [`RawStridedRef::new`]/[`RawStridedMut::new`] (or asserted by the
    /// caller of the `new_unchecked` constructors), so layout equality is the
    /// complete precondition for the unsafe-free fused replay below.
    fn check_call<D, S>(
        &self,
        dest: &RawStridedMut<'_, D>,
        src: &RawStridedRef<'_, S>,
    ) -> Result<()> {
        if dest.dims() != &self.dims[..]
            || src.dims() != &self.dims[..]
            || dest.strides() != &self.dst_strides[..]
            || src.strides() != &self.src_strides[..]
        {
            return Err(StridedError::PlanLayoutMismatch);
        }
        Ok(())
    }

    /// `dest = src` into a potentially uninitialized destination.
    ///
    /// On success every reachable logical destination element is initialized.
    /// Non-reachable holes in the backing allocation are not written.
    pub fn execute_uninit<T>(
        &self,
        dest: &mut RawStridedMut<'_, MaybeUninit<T>>,
        src: &RawStridedRef<'_, T>,
    ) -> Result<()>
    where
        T: Copy + MaybeSendSync,
    {
        self.check_call(dest, src)?;
        match &self.fused {
            Some(layout) => {
                apply_fused_pair(
                    dest,
                    src,
                    layout,
                    |dst, value| {
                        dst.write(value);
                    },
                    |value| value,
                );
                Ok(())
            }
            None => map_raw_into::<MaybeUninit<T>, T, Identity>(dest, src, MaybeUninit::new),
        }
    }

    /// `dest = src`. Allocation-free for ranks at most [`RAW_FUSED_RANK_LIMIT`](crate::RAW_FUSED_RANK_LIMIT).
    pub fn execute<T>(
        &self,
        dest: &mut RawStridedMut<'_, T>,
        src: &RawStridedRef<'_, T>,
    ) -> Result<()>
    where
        T: Copy + MaybeSendSync,
    {
        self.check_call(dest, src)?;
        match &self.fused {
            Some(layout) => {
                apply_fused_pair(
                    dest,
                    src,
                    layout,
                    |dst, value| *dst = value,
                    |value: T| value,
                );
                Ok(())
            }
            None => copy_into(&mut dest.as_view_mut(), &src.as_view()),
        }
    }

    /// `dest = scale * src`. Allocation-free for ranks at most
    /// [`RAW_FUSED_RANK_LIMIT`](crate::RAW_FUSED_RANK_LIMIT).
    pub fn execute_scale<T>(
        &self,
        dest: &mut RawStridedMut<'_, T>,
        src: &RawStridedRef<'_, T>,
        scale: T,
    ) -> Result<()>
    where
        T: Copy + Mul<T, Output = T> + MaybeSendSync,
    {
        self.check_call(dest, src)?;
        match &self.fused {
            Some(layout) => {
                apply_fused_pair(
                    dest,
                    src,
                    layout,
                    |dst, value| *dst = value,
                    |value: T| scale * value,
                );
                Ok(())
            }
            None => copy_scale(&mut dest.as_view_mut(), &src.as_view(), scale),
        }
    }

    /// `dest = conj(src)`. Allocation-free for ranks at most
    /// [`RAW_FUSED_RANK_LIMIT`](crate::RAW_FUSED_RANK_LIMIT).
    pub fn execute_conj<T>(
        &self,
        dest: &mut RawStridedMut<'_, T>,
        src: &RawStridedRef<'_, T>,
    ) -> Result<()>
    where
        T: Copy + ElementOpApply + MaybeSendSync,
    {
        self.check_call(dest, src)?;
        match &self.fused {
            Some(layout) => {
                apply_fused_pair(
                    dest,
                    src,
                    layout,
                    |dst, value| *dst = value,
                    |value: T| value.conj(),
                );
                Ok(())
            }
            None => copy_conj(&mut dest.as_view_mut(), &src.as_view()),
        }
    }
}

#[cfg(test)]
#[path = "copy_plan/tests/tests.rs"]
mod tests;