katgpt-types 0.1.1

//! SIMD elementwise kernels — scale, add, sum, max, fused ops.
//!
//! Dispatchers + NEON/AVX2/scalar impls for:
//! - `simd_scale_inplace`, `simd_add_scalar_inplace`, `simd_fused_sub_scale_inplace`
//! - `simd_sum_f32`, `simd_add_inplace`, `simd_add_into`, `simd_max_f32`
//! - `simd_fused_decay_write`, `simd_scale_mul_inplace`
//!
//! AVX2 paths share horizontal reducers from `super::horizontal`.

// x86_64 dispatch helpers from the parent `simd` module. Gated so other
// architectures don't see an unused-import warning.
#[cfg(target_arch = "x86_64")]
use super::horizontal::{horizontal_max_256, horizontal_sum_256};
#[cfg(target_arch = "x86_64")]
use super::is_avx2_fma_available;

// ── Scale Inplace ─────────────────────────────────────────────

/// SIMD-accelerated in-place scale: `x[i] *= scale` for all `i`.
///
/// General utility for softmax normalize, rmsnorm scale, HLA decay,
/// TurboQuant normalize, and any bulk `*= scale` pattern.
///
/// NEON: 4× f32 per op. AVX2: 8× f32 per op. Scalar fallback for remainder.
#[inline(always)]
pub fn simd_scale_inplace(x: &mut [f32], scale: f32) {
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_scale_inplace(x, scale) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_scale_inplace(x, scale) }
        } else {
            scalar_scale_inplace(x, scale)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_scale_inplace(x, scale) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_scale_inplace(x, scale)
    }
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_scale_inplace(x: &mut [f32], scale: f32) {
    for val in x.iter_mut() {
        *val *= scale;
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_scale_inplace(x: &mut [f32], scale: f32) {
    use core::arch::aarch64::{vdupq_n_f32, vld1q_f32, vmulq_f32, vst1q_f32};

    unsafe {
        let vs = vdupq_n_f32(scale);
        let mut i = 0;
        let chunks = x.len() / 4;

        for _ in 0..chunks {
            let vx = vld1q_f32(x.as_ptr().add(i));
            let result = vmulq_f32(vx, vs);
            vst1q_f32(x.as_mut_ptr().add(i), result);
            i += 4;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) *= scale;
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_scale_inplace(x: &mut [f32], scale: f32) {
    use core::arch::x86_64::{_mm256_loadu_ps, _mm256_mul_ps, _mm256_set1_ps, _mm256_storeu_ps};

    unsafe {
        let vs = _mm256_set1_ps(scale);
        let mut i = 0;
        let chunks = x.len() / 8;

        for _ in 0..chunks {
            let vx = _mm256_loadu_ps(x.as_ptr().add(i));
            let result = _mm256_mul_ps(vx, vs);
            _mm256_storeu_ps(x.as_mut_ptr().add(i), result);
            i += 8;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) *= scale;
            i += 1;
        }
    }
}

/// SIMD-accelerated in-place broadcast add: `x[i] += val` for all `i`.
///
/// Used for softmax max-subtraction: `scores[i] -= max_score`.
/// NEON: 4× f32 per `vaddq_f32`. AVX2: 8× f32 per `_mm256_add_ps`.
#[inline(always)]
pub fn simd_add_scalar_inplace(x: &mut [f32], val: f32) {
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_add_scalar_inplace(x, val) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_add_scalar_inplace(x, val) }
        } else {
            scalar_add_scalar_inplace(x, val)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_add_scalar_inplace(x, val) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_add_scalar_inplace(x, val)
    }
}

/// SIMD-accelerated fused subtract and scale: `x[i] = (x[i] - sub) * scale` for all `i`.
///
/// Fuses two operations into one pass, saving one full SIMD traversal vs separate
/// `simd_add_scalar_inplace` + `simd_scale_inplace`.
#[inline(always)]
pub fn simd_fused_sub_scale_inplace(x: &mut [f32], sub: f32, scale: f32) {
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_fused_sub_scale_inplace(x, sub, scale) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_fused_sub_scale_inplace(x, sub, scale) }
        } else {
            scalar_fused_sub_scale_inplace(x, sub, scale)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_fused_sub_scale_inplace(x, sub, scale) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_fused_sub_scale_inplace(x, sub, scale)
    }
}

/// SIMD-accelerated horizontal sum: returns `x[0] + x[1] + ... + x[n-1]`.
///
/// Used for softmax denominator computation (sum of exp-shifted scores).
/// NEON: uses `vaddvq_f32` for 4-lane horizontal sum. AVX2: uses 8-lane reduce.
#[inline(always)]
pub fn simd_sum_f32(x: &[f32]) -> f32 {
    if x.is_empty() {
        return 0.0;
    }
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_sum_f32(x) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_sum_f32(x) }
        } else {
            scalar_sum_f32(x)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_sum_f32(x) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_sum_f32(x)
    }
}

/// SIMD-accelerated masked sum + count: returns `(sum(x[i] where mask[i] != 0),
/// count of mask[i] != 0)`.
///
/// Used by the paired-loss-gap diagnostic's `TopKNoCopy` filter (Plan 335
/// Phase 2) and any consumer that needs a stratified sum over a boolean mask.
/// The mask is `&[u8]` (1 byte per element) for cross-platform SIMD
/// compatibility (NEON `vcgtq_u8`, AVX2 `_mm256_cmpgt_epi8`).
///
/// # Why this exists (vs `simd_sum_f32`)
///
/// LLVM does NOT auto-vectorize horizontal f32 accumulation on most targets
/// (f32 addition is non-associative; reordering changes the result). The
/// plain `for i in 0..len { sum += x[i] * mask[i] }` form compiles to scalar
/// `fadd` (~2.5 cycles/element on ARM64). This dispatcher uses explicit NEON
/// `vfmaq_f32` / AVX2 `_mm256_fmadd_ps` to hit ~4–8 elements/cycle.
///
/// NEON: 4× f32 per masked-FMA. AVX2: 8× f32 per masked-FMA.
#[inline(always)]
pub fn simd_masked_sum_count_f32(x: &[f32], mask: &[u8]) -> (f32, u32) {
    debug_assert_eq!(
        x.len(),
        mask.len(),
        "simd_masked_sum_count_f32: x.len() ({}) must equal mask.len() ({})",
        x.len(),
        mask.len()
    );
    if x.is_empty() {
        return (0.0, 0);
    }
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_masked_sum_count_f32(x, mask) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_masked_sum_count_f32(x, mask) }
        } else {
            scalar_masked_sum_count_f32(x, mask)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_masked_sum_count_f32(x, mask) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_masked_sum_count_f32(x, mask)
    }
}

/// SIMD-accelerated in-place add: `dst[i] += src[i]` for all `i`.
///
/// Used for residual connections in transformer forward pass (attn + MLP).
/// NEON: 4× f32 per `vaddq_f32`. AVX2: 8× f32 per `_mm256_add_ps`.
#[inline(always)]
pub fn simd_add_inplace(dst: &mut [f32], src: &[f32]) {
    debug_assert_eq!(
        dst.len(),
        src.len(),
        "simd_add_inplace: slices must have equal length"
    );
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_add_inplace(dst, src) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_add_inplace(dst, src) }
        } else {
            scalar_add_inplace(dst, src)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_add_inplace(dst, src) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_add_inplace(dst, src)
    }
}

/// SIMD-accelerated zip add: `dst[i] = a[i] + b[i]` for all `i`.
///
/// Used for embedding addition (wte + wpe) in transformer forward pass.
/// NEON: 4× f32 per `vaddq_f32`. AVX2: 8× f32 per `_mm256_add_ps`.
#[inline(always)]
pub fn simd_add_into(dst: &mut [f32], a: &[f32], b: &[f32]) {
    debug_assert_eq!(
        dst.len(),
        a.len(),
        "simd_add_into: dst and a must have equal length"
    );
    debug_assert_eq!(
        dst.len(),
        b.len(),
        "simd_add_into: dst and b must have equal length"
    );
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_add_into(dst, a, b) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_add_into(dst, a, b) }
        } else {
            scalar_add_into(dst, a, b)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_add_into(dst, a, b) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_add_into(dst, a, b)
    }
}

/// SIMD-accelerated max reduction: returns the maximum value in `x`.
///
/// Used for softmax numerical stability (pass 1 max-finding).
/// NEON: 4× f32 per `vmaxq_f32`. AVX2: 8× f32 per `_mm256_max_ps`.
#[inline(always)]
pub fn simd_max_f32(x: &[f32]) -> f32 {
    if x.is_empty() {
        return f32::NEG_INFINITY;
    }
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_max_f32(x) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_max_f32(x) }
        } else {
            scalar_max_f32(x)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_max_f32(x) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_max_f32(x)
    }
}

/// SIMD-accelerated fused decay-write: `dst[i] = decay * dst[i] + write * src[i]`.
///
/// Used for Raven KV cache update (exponential moving average with gating).
/// NEON: fused via `vfmaq_f32`. AVX2: fused via `_mm256_fmadd_ps`.
#[inline(always)]
pub fn simd_fused_decay_write(dst: &mut [f32], decay: f32, src: &[f32], write: f32) {
    debug_assert_eq!(
        dst.len(),
        src.len(),
        "simd_fused_decay_write: slices must have equal length"
    );
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_fused_decay_write(dst, decay, src, write) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_fused_decay_write(dst, decay, src, write) }
        } else {
            scalar_fused_decay_write(dst, decay, src, write)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_fused_decay_write(dst, decay, src, write) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_fused_decay_write(dst, decay, src, write)
    }
}

/// SIMD-accelerated fused scale+multiply: `x[i] = gamma[i] * x[i] * scale`.
///
/// Used for `rmsnorm_with_gamma`: fuses the inv_rms scale and learnable gamma
/// multiply into a single pass, saving one full buffer scan vs separate
/// `simd_scale_inplace` + elementwise multiply.
///
/// NEON: fused via `vmulq_f32` (2 multiplies per 4 elements).
/// AVX2: fused via `_mm256_mul_ps` (2 multiplies per 8 elements).
#[inline(always)]
pub fn simd_scale_mul_inplace(x: &mut [f32], gamma: &[f32], scale: f32) {
    debug_assert_eq!(
        x.len(),
        gamma.len(),
        "simd_scale_mul_inplace: slices must have equal length"
    );
    #[cfg(target_arch = "aarch64")]
    {
        unsafe { neon_scale_mul_inplace(x, gamma, scale) }
    }
    #[cfg(target_arch = "x86_64")]
    {
        if is_avx2_fma_available() {
            unsafe { avx2_scale_mul_inplace(x, gamma, scale) }
        } else {
            scalar_scale_mul_inplace(x, gamma, scale)
        }
    }
    #[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
    {
        unsafe { wasm32_simd128_scale_mul_inplace(x, gamma, scale) }
    }
    #[cfg(not(any(
        target_arch = "aarch64",
        target_arch = "x86_64",
        all(target_arch = "wasm32", target_feature = "simd128")
    )))]
    {
        scalar_scale_mul_inplace(x, gamma, scale)
    }
}

// ── Scalar Fallbacks (new primitives) ─────────────────────────

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_add_inplace(dst: &mut [f32], src: &[f32]) {
    for i in 0..dst.len() {
        unsafe {
            *dst.get_unchecked_mut(i) += *src.get_unchecked(i);
        }
    }
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_add_scalar_inplace(x: &mut [f32], val: f32) {
    for v in x.iter_mut() {
        *v += val;
    }
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_fused_sub_scale_inplace(x: &mut [f32], sub: f32, scale: f32) {
    // Rewrite (v - sub) * scale as v * scale + (-sub * scale) to enable FMA.
    // The additive term is loop-invariant — hoist outside the per-element work.
    let bias = -(sub * scale);
    for v in x.iter_mut() {
        *v = v.mul_add(scale, bias);
    }
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_sum_f32(x: &[f32]) -> f32 {
    // 4 independent accumulators — addition is latency-bound on a single
    // accumulator (~3 cycles/iter on most FPUs). Unrolling 4-wide keeps the
    // adder pipeline full and helps LLVM auto-vectorize on targets without
    // dedicated f32 SIMD.
    let mut acc = [0.0f32; 4];
    let chunks = x.len() / 4;
    let mut i = 0;
    for _ in 0..chunks {
        unsafe {
            acc[0] += *x.get_unchecked(i);
            acc[1] += *x.get_unchecked(i + 1);
            acc[2] += *x.get_unchecked(i + 2);
            acc[3] += *x.get_unchecked(i + 3);
        }
        i += 4;
    }
    let mut sum = acc.iter().sum::<f32>();
    while i < x.len() {
        unsafe {
            sum += *x.get_unchecked(i);
        }
        i += 1;
    }
    sum
}

/// Scalar fallback for `simd_masked_sum_count_f32`. Branchless: `(mask[i] !=
/// 0) as u32` produces a 0/1 multiplier; `d * (m as f32)` and `count += m`
/// avoid the branch that would defeat pipelining.
#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_masked_sum_count_f32(x: &[f32], mask: &[u8]) -> (f32, u32) {
    let mut sum = 0.0f32;
    let mut count = 0u32;
    for i in 0..x.len() {
        unsafe {
            let m = u32::from(*mask.get_unchecked(i) != 0);
            sum += *x.get_unchecked(i) * (m as f32);
            count += m;
        }
    }
    (sum, count)
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_add_into(dst: &mut [f32], a: &[f32], b: &[f32]) {
    for i in 0..dst.len() {
        unsafe {
            *dst.get_unchecked_mut(i) = *a.get_unchecked(i) + *b.get_unchecked(i);
        }
    }
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_max_f32(x: &[f32]) -> f32 {
    let mut max = x[0];
    for i in 1..x.len() {
        // Branch-free: matches the SIMD path's vmaxq_f32 / _mm256_max_ps NaN semantics
        // (propagates NaN), unlike `if v > max` which silently drops NaN.
        max = max.max(unsafe { *x.get_unchecked(i) });
    }
    max
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_fused_decay_write(dst: &mut [f32], decay: f32, src: &[f32], write: f32) {
    for i in 0..dst.len() {
        unsafe {
            let d = *dst.get_unchecked(i);
            let s = *src.get_unchecked(i);
            // FMA: write * src + decay * dst (one FMA + one mul).
            // Picked `decay * d` as the FMA product since `decay` is typically the
            // recurrence weight (close to 1.0) — keeping it inside FMA preserves
            // the most precision in the dominant term.
            *dst.get_unchecked_mut(i) = decay.mul_add(d, write * s);
        }
    }
}

#[inline(always)]
#[allow(dead_code)]
pub(super) fn scalar_scale_mul_inplace(x: &mut [f32], gamma: &[f32], scale: f32) {
    // No FMA opportunity: x[i] = gamma[i] * x[i] * scale is a pure product of
    // three factors. The two-multiply form is already optimal.
    for i in 0..x.len() {
        unsafe {
            *x.get_unchecked_mut(i) = *gamma.get_unchecked(i) * *x.get_unchecked(i) * scale;
        }
    }
}

// ── NEON Backend (new primitives) ─────────────────────────────

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_add_inplace(dst: &mut [f32], src: &[f32]) {
    use core::arch::aarch64::{vaddq_f32, vld1q_f32, vst1q_f32};
    unsafe {
        let mut i = 0;
        let chunks = dst.len() / 4;
        for _ in 0..chunks {
            let vd = vld1q_f32(dst.as_ptr().add(i));
            let vs = vld1q_f32(src.as_ptr().add(i));
            let result = vaddq_f32(vd, vs);
            vst1q_f32(dst.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < dst.len() {
            *dst.get_unchecked_mut(i) += *src.get_unchecked(i);
            i += 1;
        }
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_add_scalar_inplace(x: &mut [f32], val: f32) {
    use core::arch::aarch64::{vaddq_f32, vdupq_n_f32, vld1q_f32, vst1q_f32};
    unsafe {
        let vv = vdupq_n_f32(val);
        let mut i = 0;
        let chunks = x.len() / 4;
        for _ in 0..chunks {
            let vx = vld1q_f32(x.as_ptr().add(i));
            let result = vaddq_f32(vx, vv);
            vst1q_f32(x.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < x.len() {
            *x.get_unchecked_mut(i) += val;
            i += 1;
        }
    }
}

#[cfg(target_arch = "aarch64")]
#[target_feature(enable = "neon")]
#[inline]
unsafe fn neon_fused_sub_scale_inplace(x: &mut [f32], sub: f32, scale: f32) {
    use core::arch::aarch64::{vdupq_n_f32, vld1q_f32, vmulq_f32, vst1q_f32, vsubq_f32};
    unsafe {
        let sub_vec = vdupq_n_f32(sub);
        let scale_vec = vdupq_n_f32(scale);
        let mut i = 0;
        let chunks = x.len() / 4;
        for _ in 0..chunks {
            let v = vld1q_f32(x.as_ptr().add(i));
            let result = vmulq_f32(vsubq_f32(v, sub_vec), scale_vec);
            vst1q_f32(x.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < x.len() {
            *x.get_unchecked_mut(i) = (*x.get_unchecked(i) - sub) * scale;
            i += 1;
        }
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_sum_f32(x: &[f32]) -> f32 {
    use core::arch::aarch64::{vaddq_f32, vaddvq_f32, vdupq_n_f32, vld1q_f32};
    unsafe {
        // 4 independent accumulators to hide FADD pipeline latency.
        // The serial single-accumulator reduction is latency-bound (each add
        // depends on the previous); 4 lanes let the pipeline stay full.
        // Same associativity-reorder already used by `neon_dot_f32`.
        let mut acc0 = vdupq_n_f32(0.0);
        let mut acc1 = vdupq_n_f32(0.0);
        let mut acc2 = vdupq_n_f32(0.0);
        let mut acc3 = vdupq_n_f32(0.0);
        let mut i = 0;
        let len = x.len();
        let chunks4 = len / 16;

        for _ in 0..chunks4 {
            acc0 = vaddq_f32(acc0, vld1q_f32(x.as_ptr().add(i)));
            acc1 = vaddq_f32(acc1, vld1q_f32(x.as_ptr().add(i + 4)));
            acc2 = vaddq_f32(acc2, vld1q_f32(x.as_ptr().add(i + 8)));
            acc3 = vaddq_f32(acc3, vld1q_f32(x.as_ptr().add(i + 12)));
            i += 16;
        }

        // Horizontal reduce: acc0+acc1+acc2+acc3
        let mut sum = vaddvq_f32(vaddq_f32(vaddq_f32(acc0, acc1), vaddq_f32(acc2, acc3)));

        let mut acc_rem = vdupq_n_f32(0.0);
        let remaining = (len - i) / 4;
        for _ in 0..remaining {
            acc_rem = vaddq_f32(acc_rem, vld1q_f32(x.as_ptr().add(i)));
            i += 4;
        }
        sum += vaddvq_f32(acc_rem);

        while i < len {
            sum += *x.get_unchecked(i);
            i += 1;
        }
        sum
    }
}

/// NEON masked sum + count for `simd_masked_sum_count_f32`. Loads 4 f32
/// values per iteration, multiplies by a 0.0/1.0 mask (built from the u8
/// mask bytes), and accumulates with 4 independent accumulators (same
/// latency-hiding trick as `neon_sum_f32`). The mask conversion (u8→f32)
/// uses a stack `[f32; 4]` load — the scalar conversions are cheap relative
/// to the vectorized FMA, and the approach avoids needing a u8→u32 widening
/// chain.
#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_masked_sum_count_f32(x: &[f32], mask: &[u8]) -> (f32, u32) {
    use core::arch::aarch64::{vaddq_f32, vaddvq_f32, vdupq_n_f32, vld1q_f32, vmulq_f32};
    unsafe {
        let zero = vdupq_n_f32(0.0);
        let mut acc_sum0 = zero;
        let mut acc_sum1 = zero;
        let mut acc_sum2 = zero;
        let mut acc_sum3 = zero;
        let mut count: u32 = 0;
        let mut i = 0;
        let len = x.len();
        let chunks4 = len / 16;

        for _ in 0..chunks4 {
            // 4-lane mask as f32 (0.0 or 1.0).
            let m0 = mask_f32_4(mask, i);
            let m1 = mask_f32_4(mask, i + 4);
            let m2 = mask_f32_4(mask, i + 8);
            let m3 = mask_f32_4(mask, i + 12);
            let x0 = vld1q_f32(x.as_ptr().add(i));
            let x1 = vld1q_f32(x.as_ptr().add(i + 4));
            let x2 = vld1q_f32(x.as_ptr().add(i + 8));
            let x3 = vld1q_f32(x.as_ptr().add(i + 12));
            // sum += x * mask (elementwise mul then add).
            acc_sum0 = vaddq_f32(acc_sum0, vmulq_f32(x0, m0));
            acc_sum1 = vaddq_f32(acc_sum1, vmulq_f32(x1, m1));
            acc_sum2 = vaddq_f32(acc_sum2, vmulq_f32(x2, m2));
            acc_sum3 = vaddq_f32(acc_sum3, vmulq_f32(x3, m3));
            count += mask_count_4(mask, i)
                + mask_count_4(mask, i + 4)
                + mask_count_4(mask, i + 8)
                + mask_count_4(mask, i + 12);
            i += 16;
        }

        let mut sum = vaddvq_f32(vaddq_f32(
            vaddq_f32(acc_sum0, acc_sum1),
            vaddq_f32(acc_sum2, acc_sum3),
        ));

        // Remaining full 4-lanes.
        let remaining = (len - i) / 4;
        let mut acc_rem = zero;
        for _ in 0..remaining {
            let m = mask_f32_4(mask, i);
            let xv = vld1q_f32(x.as_ptr().add(i));
            acc_rem = vaddq_f32(acc_rem, vmulq_f32(xv, m));
            count += mask_count_4(mask, i);
            i += 4;
        }
        sum += vaddvq_f32(acc_rem);

        // Tail.
        while i < len {
            let m = u32::from(*mask.get_unchecked(i) != 0);
            sum += *x.get_unchecked(i) * (m as f32);
            count += m;
            i += 1;
        }
        (sum, count)
    }
}

/// Helper: load 4 u8 mask values (at offsets `i..i+4`) as a NEON f32x4 of
/// 0.0/1.0. Uses a stack `[f32; 4]` intermediate — the scalar conversions
/// are cheap (1 cycle each) and the load is vectorized.
#[cfg(target_arch = "aarch64")]
#[inline(always)]
unsafe fn mask_f32_4(mask: &[u8], i: usize) -> core::arch::aarch64::float32x4_t {
    use core::arch::aarch64::vld1q_f32;
    unsafe {
        let m = [
            ((*mask.get_unchecked(i) != 0) as u8) as f32,
            ((*mask.get_unchecked(i + 1) != 0) as u8) as f32,
            ((*mask.get_unchecked(i + 2) != 0) as u8) as f32,
            ((*mask.get_unchecked(i + 3) != 0) as u8) as f32,
        ];
        vld1q_f32(m.as_ptr())
    }
}

/// Helper: count non-zero mask values in `mask[i..i+4]`.
#[cfg(target_arch = "aarch64")]
#[inline(always)]
unsafe fn mask_count_4(mask: &[u8], i: usize) -> u32 {
    unsafe {
        u32::from(*mask.get_unchecked(i) != 0)
            + u32::from(*mask.get_unchecked(i + 1) != 0)
            + u32::from(*mask.get_unchecked(i + 2) != 0)
            + u32::from(*mask.get_unchecked(i + 3) != 0)
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_add_into(dst: &mut [f32], a: &[f32], b: &[f32]) {
    use core::arch::aarch64::{vaddq_f32, vld1q_f32, vst1q_f32};
    unsafe {
        let mut i = 0;
        let chunks = dst.len() / 4;
        for _ in 0..chunks {
            let va = vld1q_f32(a.as_ptr().add(i));
            let vb = vld1q_f32(b.as_ptr().add(i));
            let result = vaddq_f32(va, vb);
            vst1q_f32(dst.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < dst.len() {
            *dst.get_unchecked_mut(i) = *a.get_unchecked(i) + *b.get_unchecked(i);
            i += 1;
        }
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_max_f32(x: &[f32]) -> f32 {
    use core::arch::aarch64::{vld1q_f32, vmaxq_f32, vmaxvq_f32};
    unsafe {
        let len = x.len();
        let chunks = len / 4;
        if chunks == 0 {
            let mut max = x[0];
            for j in 1..len {
                let v = *x.get_unchecked(j);
                if v > max {
                    max = v;
                }
            }
            return max;
        }

        // 4 independent vector-max accumulators to hide the max-op latency.
        // max is associative + commutative, so this is bit-identical to serial.
        let mut vmax0 = vld1q_f32(x.as_ptr());
        let mut vmax1 = vmax0;
        let mut vmax2 = vmax0;
        let mut vmax3 = vmax0;
        let mut i = 0;
        let chunks4 = len / 16;
        for _ in 0..chunks4 {
            vmax0 = vmaxq_f32(vmax0, vld1q_f32(x.as_ptr().add(i)));
            vmax1 = vmaxq_f32(vmax1, vld1q_f32(x.as_ptr().add(i + 4)));
            vmax2 = vmaxq_f32(vmax2, vld1q_f32(x.as_ptr().add(i + 8)));
            vmax3 = vmaxq_f32(vmax3, vld1q_f32(x.as_ptr().add(i + 12)));
            i += 16;
        }
        let mut vmax = vmaxq_f32(vmaxq_f32(vmax0, vmax1), vmaxq_f32(vmax2, vmax3));
        // Remaining 4-element chunks
        while i + 4 <= len {
            vmax = vmaxq_f32(vmax, vld1q_f32(x.as_ptr().add(i)));
            i += 4;
        }

        // Horizontal max of 4 lanes — single `vmaxvq_f32` instruction replaces
        // the transmute + scalar loop. Mandatory on ARMv8+.
        let mut max = vmaxvq_f32(vmax);

        // Handle tail
        while i < len {
            let v = *x.get_unchecked(i);
            if v > max {
                max = v;
            }
            i += 1;
        }
        max
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_fused_decay_write(dst: &mut [f32], decay: f32, src: &[f32], write: f32) {
    use core::arch::aarch64::{vdupq_n_f32, vfmaq_f32, vld1q_f32, vmulq_f32, vst1q_f32};
    unsafe {
        let vd_decay = vdupq_n_f32(decay);
        let vd_write = vdupq_n_f32(write);
        let mut i = 0;
        let chunks = dst.len() / 4;
        for _ in 0..chunks {
            let vdst = vld1q_f32(dst.as_ptr().add(i));
            let vsrc = vld1q_f32(src.as_ptr().add(i));
            // FMA: write * vsrc + decay * vdst
            let result = vfmaq_f32(vmulq_f32(vdst, vd_decay), vsrc, vd_write);
            vst1q_f32(dst.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < dst.len() {
            *dst.get_unchecked_mut(i) =
                decay * *dst.get_unchecked(i) + write * *src.get_unchecked(i);
            i += 1;
        }
    }
}

#[cfg(target_arch = "aarch64")]
#[inline]
unsafe fn neon_scale_mul_inplace(x: &mut [f32], gamma: &[f32], scale: f32) {
    use core::arch::aarch64::{vdupq_n_f32, vld1q_f32, vmulq_f32, vst1q_f32};
    unsafe {
        let vs = vdupq_n_f32(scale);
        let mut i = 0;
        let chunks = x.len() / 4;
        for _ in 0..chunks {
            let vx = vld1q_f32(x.as_ptr().add(i));
            let vg = vld1q_f32(gamma.as_ptr().add(i));
            let result = vmulq_f32(vg, vmulq_f32(vx, vs));
            vst1q_f32(x.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < x.len() {
            *x.get_unchecked_mut(i) = *gamma.get_unchecked(i) * *x.get_unchecked(i) * scale;
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_add_inplace(dst: &mut [f32], src: &[f32]) {
    use core::arch::x86_64::{_mm256_add_ps, _mm256_loadu_ps, _mm256_storeu_ps};
    unsafe {
        let mut i = 0;
        let chunks = dst.len() / 8;
        for _ in 0..chunks {
            let vd = _mm256_loadu_ps(dst.as_ptr().add(i));
            let vs = _mm256_loadu_ps(src.as_ptr().add(i));
            let result = _mm256_add_ps(vd, vs);
            _mm256_storeu_ps(dst.as_mut_ptr().add(i), result);
            i += 8;
        }
        while i < dst.len() {
            *dst.get_unchecked_mut(i) += *src.get_unchecked(i);
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_add_scalar_inplace(x: &mut [f32], val: f32) {
    use core::arch::x86_64::{_mm256_add_ps, _mm256_loadu_ps, _mm256_set1_ps, _mm256_storeu_ps};
    unsafe {
        let vv = _mm256_set1_ps(val);
        let mut i = 0;
        let chunks = x.len() / 8;
        for _ in 0..chunks {
            let vx = _mm256_loadu_ps(x.as_ptr().add(i));
            let result = _mm256_add_ps(vx, vv);
            _mm256_storeu_ps(x.as_mut_ptr().add(i), result);
            i += 8;
        }
        while i < x.len() {
            *x.get_unchecked_mut(i) += val;
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_fused_sub_scale_inplace(x: &mut [f32], sub: f32, scale: f32) {
    use core::arch::x86_64::{
        _mm_loadu_ps, _mm_mul_ps, _mm_set1_ps, _mm_storeu_ps, _mm_sub_ps, _mm256_loadu_ps,
        _mm256_mul_ps, _mm256_set1_ps, _mm256_storeu_ps, _mm256_sub_ps,
    };
    unsafe {
        let sub_vec = _mm256_set1_ps(sub);
        let scale_vec = _mm256_set1_ps(scale);
        let mut i = 0;
        let chunks = x.len() / 8;
        for _ in 0..chunks {
            let v = _mm256_loadu_ps(x.as_ptr().add(i));
            let subbed = _mm256_sub_ps(v, sub_vec);
            let result = _mm256_mul_ps(subbed, scale_vec);
            _mm256_storeu_ps(x.as_mut_ptr().add(i), result);
            i += 8;
        }
        // Handle remaining 4-element chunk with SSE
        if i + 4 <= x.len() {
            let sub_128 = _mm_set1_ps(sub);
            let scale_128 = _mm_set1_ps(scale);
            let v = _mm_loadu_ps(x.as_ptr().add(i));
            let subbed = _mm_sub_ps(v, sub_128);
            let result = _mm_mul_ps(subbed, scale_128);
            _mm_storeu_ps(x.as_mut_ptr().add(i), result);
            i += 4;
        }
        while i < x.len() {
            *x.get_unchecked_mut(i) = (*x.get_unchecked(i) - sub) * scale;
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_sum_f32(x: &[f32]) -> f32 {
    use core::arch::x86_64::{_mm256_add_ps, _mm256_loadu_ps, _mm256_setzero_ps};
    unsafe {
        // 4 independent accumulators to hide FADD pipeline latency.
        // Same associativity-reorder already used by `avx2_dot_f32`.
        let mut acc0 = _mm256_setzero_ps();
        let mut acc1 = _mm256_setzero_ps();
        let mut acc2 = _mm256_setzero_ps();
        let mut acc3 = _mm256_setzero_ps();
        let mut i = 0;
        let len = x.len();
        let chunks4 = len / 32;

        for _ in 0..chunks4 {
            acc0 = _mm256_add_ps(acc0, _mm256_loadu_ps(x.as_ptr().add(i)));
            acc1 = _mm256_add_ps(acc1, _mm256_loadu_ps(x.as_ptr().add(i + 8)));
            acc2 = _mm256_add_ps(acc2, _mm256_loadu_ps(x.as_ptr().add(i + 16)));
            acc3 = _mm256_add_ps(acc3, _mm256_loadu_ps(x.as_ptr().add(i + 24)));
            i += 32;
        }

        // Horizontal reduce: acc0+acc1+acc2+acc3
        let mut sum = horizontal_sum_256(_mm256_add_ps(
            _mm256_add_ps(acc0, acc1),
            _mm256_add_ps(acc2, acc3),
        ));

        let mut acc = _mm256_setzero_ps();
        let remaining = (len - i) / 8;
        for _ in 0..remaining {
            acc = _mm256_add_ps(acc, _mm256_loadu_ps(x.as_ptr().add(i)));
            i += 8;
        }
        sum += horizontal_sum_256(acc);

        while i < len {
            sum += *x.get_unchecked(i);
            i += 1;
        }
        sum
    }
}

/// AVX2 masked sum + count for `simd_masked_sum_count_f32`. Loads 8 f32
/// values + 8 u8 mask values per iteration, widens u8→u32→f32 via
/// `_mm256_cvtepu8_epi32` + `_mm256_cvtepi32_ps`, multiplies, and accumulates.
/// 4 independent accumulators hide the FADD/FMA latency (same as `avx2_sum_f32`).
#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_masked_sum_count_f32(x: &[f32], mask: &[u8]) -> (f32, u32) {
    use core::arch::x86_64::{
        _mm_loadu_si128, _mm256_add_ps, _mm256_cvtepi32_ps, _mm256_cvtepu8_epi32, _mm256_loadu_ps,
        _mm256_mul_ps, _mm256_setzero_ps,
    };
    unsafe {
        let zero = _mm256_setzero_ps();
        let mut acc0 = zero;
        let mut acc1 = zero;
        let mut acc2 = zero;
        let mut acc3 = zero;
        let mut count: u32 = 0;
        let mut i = 0;
        let len = x.len();
        let chunks4 = len / 32;

        for _ in 0..chunks4 {
            // Load 8 u8 mask values, widen to 8×u32, convert to 8×f32.
            let m_raw0 = _mm_loadu_si128(mask.as_ptr().add(i) as *const _);
            let m0 = _mm256_cvtepi32_ps(_mm256_cvtepu8_epi32(m_raw0));
            let m_raw1 = _mm_loadu_si128(mask.as_ptr().add(i + 8) as *const _);
            let m1 = _mm256_cvtepi32_ps(_mm256_cvtepu8_epi32(m_raw1));
            let m_raw2 = _mm_loadu_si128(mask.as_ptr().add(i + 16) as *const _);
            let m2 = _mm256_cvtepi32_ps(_mm256_cvtepu8_epi32(m_raw2));
            let m_raw3 = _mm_loadu_si128(mask.as_ptr().add(i + 24) as *const _);
            let m3 = _mm256_cvtepi32_ps(_mm256_cvtepu8_epi32(m_raw3));
            let x0 = _mm256_loadu_ps(x.as_ptr().add(i));
            let x1 = _mm256_loadu_ps(x.as_ptr().add(i + 8));
            let x2 = _mm256_loadu_ps(x.as_ptr().add(i + 16));
            let x3 = _mm256_loadu_ps(x.as_ptr().add(i + 24));
            acc0 = _mm256_add_ps(acc0, _mm256_mul_ps(x0, m0));
            acc1 = _mm256_add_ps(acc1, _mm256_mul_ps(x1, m1));
            acc2 = _mm256_add_ps(acc2, _mm256_mul_ps(x2, m2));
            acc3 = _mm256_add_ps(acc3, _mm256_mul_ps(x3, m3));
            count += mask_count_8(mask, i)
                + mask_count_8(mask, i + 8)
                + mask_count_8(mask, i + 16)
                + mask_count_8(mask, i + 24);
            i += 32;
        }

        let mut sum = horizontal_sum_256(_mm256_add_ps(
            _mm256_add_ps(acc0, acc1),
            _mm256_add_ps(acc2, acc3),
        ));

        let remaining = (len - i) / 8;
        let mut acc = zero;
        for _ in 0..remaining {
            let m_raw = _mm_loadu_si128(mask.as_ptr().add(i) as *const _);
            let m = _mm256_cvtepi32_ps(_mm256_cvtepu8_epi32(m_raw));
            let xv = _mm256_loadu_ps(x.as_ptr().add(i));
            acc = _mm256_add_ps(acc, _mm256_mul_ps(xv, m));
            count += mask_count_8(mask, i);
            i += 8;
        }
        sum += horizontal_sum_256(acc);

        while i < len {
            let m = u32::from(*mask.get_unchecked(i) != 0);
            sum += *x.get_unchecked(i) * (m as f32);
            count += m;
            i += 1;
        }
        (sum, count)
    }
}

/// Helper: count non-zero mask values in `mask[i..i+8]`. (x86_64 backend.)
#[cfg(target_arch = "x86_64")]
#[inline(always)]
unsafe fn mask_count_8(mask: &[u8], i: usize) -> u32 {
    unsafe {
        u32::from(*mask.get_unchecked(i) != 0)
            + u32::from(*mask.get_unchecked(i + 1) != 0)
            + u32::from(*mask.get_unchecked(i + 2) != 0)
            + u32::from(*mask.get_unchecked(i + 3) != 0)
            + u32::from(*mask.get_unchecked(i + 4) != 0)
            + u32::from(*mask.get_unchecked(i + 5) != 0)
            + u32::from(*mask.get_unchecked(i + 6) != 0)
            + u32::from(*mask.get_unchecked(i + 7) != 0)
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_add_into(dst: &mut [f32], a: &[f32], b: &[f32]) {
    use core::arch::x86_64::{_mm256_add_ps, _mm256_loadu_ps, _mm256_storeu_ps};
    unsafe {
        let mut i = 0;
        let chunks = dst.len() / 8;
        for _ in 0..chunks {
            let va = _mm256_loadu_ps(a.as_ptr().add(i));
            let vb = _mm256_loadu_ps(b.as_ptr().add(i));
            let result = _mm256_add_ps(va, vb);
            _mm256_storeu_ps(dst.as_mut_ptr().add(i), result);
            i += 8;
        }
        while i < dst.len() {
            *dst.get_unchecked_mut(i) = *a.get_unchecked(i) + *b.get_unchecked(i);
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_max_f32(x: &[f32]) -> f32 {
    use core::arch::x86_64::{_mm256_loadu_ps, _mm256_max_ps};
    unsafe {
        let len = x.len();
        let chunks = len / 8;
        if chunks == 0 {
            let mut max = x[0];
            for j in 1..len {
                let v = *x.get_unchecked(j);
                if v > max {
                    max = v;
                }
            }
            return max;
        }

        // 4 independent vector-max accumulators to hide the max-op latency.
        // max is associative + commutative, so this is bit-identical to serial.
        let mut vmax0 = _mm256_loadu_ps(x.as_ptr());
        let mut vmax1 = vmax0;
        let mut vmax2 = vmax0;
        let mut vmax3 = vmax0;
        let mut i = 0;
        let chunks4 = len / 32;
        for _ in 0..chunks4 {
            vmax0 = _mm256_max_ps(vmax0, _mm256_loadu_ps(x.as_ptr().add(i)));
            vmax1 = _mm256_max_ps(vmax1, _mm256_loadu_ps(x.as_ptr().add(i + 8)));
            vmax2 = _mm256_max_ps(vmax2, _mm256_loadu_ps(x.as_ptr().add(i + 16)));
            vmax3 = _mm256_max_ps(vmax3, _mm256_loadu_ps(x.as_ptr().add(i + 24)));
            i += 32;
        }
        let mut vmax = _mm256_max_ps(_mm256_max_ps(vmax0, vmax1), _mm256_max_ps(vmax2, vmax3));
        // Remaining 8-element chunks
        while i + 8 <= len {
            vmax = _mm256_max_ps(vmax, _mm256_loadu_ps(x.as_ptr().add(i)));
            i += 8;
        }

        // Horizontal max reduction
        let mut max = horizontal_max_256(vmax);

        // Handle tail
        while i < len {
            let v = *x.get_unchecked(i);
            if v > max {
                max = v;
            }
            i += 1;
        }
        max
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_fused_decay_write(dst: &mut [f32], decay: f32, src: &[f32], write: f32) {
    use core::arch::x86_64::{
        _mm256_add_ps, _mm256_loadu_ps, _mm256_mul_ps, _mm256_set1_ps, _mm256_storeu_ps,
    };

    unsafe {
        let vd = _mm256_set1_ps(decay);
        let vw = _mm256_set1_ps(write);
        let mut i = 0;
        let chunks = dst.len() / 8;

        for _ in 0..chunks {
            let vdst = _mm256_loadu_ps(dst.as_ptr().add(i));
            let vsrc = _mm256_loadu_ps(src.as_ptr().add(i));
            let result = _mm256_add_ps(_mm256_mul_ps(vd, vdst), _mm256_mul_ps(vw, vsrc));
            _mm256_storeu_ps(dst.as_mut_ptr().add(i), result);
            i += 8;
        }

        while i < dst.len() {
            *dst.get_unchecked_mut(i) =
                decay * *dst.get_unchecked(i) + write * *src.get_unchecked(i);
            i += 1;
        }
    }
}

#[cfg(target_arch = "x86_64")]
#[target_feature(enable = "avx2,fma")]
#[inline]
unsafe fn avx2_scale_mul_inplace(x: &mut [f32], gamma: &[f32], scale: f32) {
    use core::arch::x86_64::{_mm256_loadu_ps, _mm256_mul_ps, _mm256_set1_ps, _mm256_storeu_ps};

    unsafe {
        let vs = _mm256_set1_ps(scale);
        let mut i = 0;
        let chunks = x.len() / 8;

        for _ in 0..chunks {
            let vx = _mm256_loadu_ps(x.as_ptr().add(i));
            let vg = _mm256_loadu_ps(gamma.as_ptr().add(i));
            let result = _mm256_mul_ps(vg, _mm256_mul_ps(vx, vs));
            _mm256_storeu_ps(x.as_mut_ptr().add(i), result);
            i += 8;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) = *gamma.get_unchecked(i) * *x.get_unchecked(i) * scale;
            i += 1;
        }
    }
}

// ── WASM SIMD128 (4-wide f32) ─────────────────────────────────
//
// Issue 007: ports the NEON kernel structure to `core::arch::wasm32`.
// WASM SIMD128 base proposal has NO FMA intrinsic — every fused op below
// uses separate `f32x4_mul` + `f32x4_add` (wasmtime / engine JITs may fuse
// mul→add). Bit-identical to the scalar reference modulo FMA contraction
// (1 ULP acceptable vs the NEON `vfmaq_f32` path).
//
// Intrinsics mapping (NEON → WASM):
//   vld1q_f32(p)            → v128_load(p.cast())
//   vst1q_f32(p, v)         → v128_store(p.cast(), v)
//   vdupq_n_f32(s)          → f32x4_splat(s)
//   vaddq_f32/vmulq_f32     → f32x4_add / f32x4_mul
//   vsubq_f32               → f32x4_sub
//   vmaxq_f32               → f32x4_max
//   vaddvq_f32(v)           → sum of f32x4_extract_lane::<0..3>(v)
//   vmaxvq_f32(v)           → reduce f32x4_extract_lane::<0..3>(v) via f32::max
//   vfmaq_f32(a, b, c)=a+b*c→ f32x4_add(f32x4_mul(b, c), a)

/// WASM SIMD128 in-place scale. Mirrors `neon_scale_inplace` (4-wide).
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_scale_inplace(x: &mut [f32], scale: f32) {
    use core::arch::wasm32::{f32x4_mul, f32x4_splat, v128_load, v128_store};

    unsafe {
        let vs = f32x4_splat(scale);
        let mut i = 0;
        let chunks = x.len() / 4;

        for _ in 0..chunks {
            let vx = v128_load(x.as_ptr().add(i).cast());
            let result = f32x4_mul(vx, vs);
            v128_store(x.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) *= scale;
            i += 1;
        }
    }
}

/// WASM SIMD128 in-place broadcast add. Mirrors `neon_add_scalar_inplace`.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_add_scalar_inplace(x: &mut [f32], val: f32) {
    use core::arch::wasm32::{f32x4_add, f32x4_splat, v128_load, v128_store};

    unsafe {
        let vv = f32x4_splat(val);
        let mut i = 0;
        let chunks = x.len() / 4;

        for _ in 0..chunks {
            let vx = v128_load(x.as_ptr().add(i).cast());
            let result = f32x4_add(vx, vv);
            v128_store(x.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) += val;
            i += 1;
        }
    }
}

/// WASM SIMD128 fused subtract+scale. Mirrors `neon_fused_sub_scale_inplace`.
/// `(x[i] - sub) * scale` — pure sub→mul chain, no FMA involved.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_fused_sub_scale_inplace(x: &mut [f32], sub: f32, scale: f32) {
    use core::arch::wasm32::{f32x4_mul, f32x4_splat, f32x4_sub, v128_load, v128_store};

    unsafe {
        let sub_vec = f32x4_splat(sub);
        let scale_vec = f32x4_splat(scale);
        let mut i = 0;
        let chunks = x.len() / 4;

        for _ in 0..chunks {
            let v = v128_load(x.as_ptr().add(i).cast());
            let result = f32x4_mul(f32x4_sub(v, sub_vec), scale_vec);
            v128_store(x.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) = (*x.get_unchecked(i) - sub) * scale;
            i += 1;
        }
    }
}

/// WASM SIMD128 horizontal sum. Mirrors `neon_sum_f32` (4 independent
/// 4-lane accumulators = 16 elements per outer iter).
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_sum_f32(x: &[f32]) -> f32 {
    use core::arch::wasm32::{f32x4_add, f32x4_extract_lane, f32x4_splat, v128_load};

    unsafe {
        // 4 independent accumulators to hide FADD pipeline latency.
        // Same associativity-reorder already used by `wasm32_simd128_dot_f32`.
        let mut acc0 = f32x4_splat(0.0);
        let mut acc1 = f32x4_splat(0.0);
        let mut acc2 = f32x4_splat(0.0);
        let mut acc3 = f32x4_splat(0.0);
        let mut i = 0;
        let len = x.len();
        let chunks4 = len / 16;

        for _ in 0..chunks4 {
            acc0 = f32x4_add(acc0, v128_load(x.as_ptr().add(i).cast()));
            acc1 = f32x4_add(acc1, v128_load(x.as_ptr().add(i + 4).cast()));
            acc2 = f32x4_add(acc2, v128_load(x.as_ptr().add(i + 8).cast()));
            acc3 = f32x4_add(acc3, v128_load(x.as_ptr().add(i + 12).cast()));
            i += 16;
        }

        // Horizontal reduce: acc0+acc1+acc2+acc3 → 4 lanes → scalar
        // (replaces NEON `vaddvq_f32`).
        let s = f32x4_add(f32x4_add(acc0, acc1), f32x4_add(acc2, acc3));
        let mut sum = f32x4_extract_lane::<0>(s)
            + f32x4_extract_lane::<1>(s)
            + f32x4_extract_lane::<2>(s)
            + f32x4_extract_lane::<3>(s);

        let mut acc_rem = f32x4_splat(0.0);
        let remaining = (len - i) / 4;
        for _ in 0..remaining {
            acc_rem = f32x4_add(acc_rem, v128_load(x.as_ptr().add(i).cast()));
            i += 4;
        }
        sum += f32x4_extract_lane::<0>(acc_rem)
            + f32x4_extract_lane::<1>(acc_rem)
            + f32x4_extract_lane::<2>(acc_rem)
            + f32x4_extract_lane::<3>(acc_rem);

        while i < len {
            sum += *x.get_unchecked(i);
            i += 1;
        }
        sum
    }
}

/// WASM SIMD128 masked sum + count. Mirrors `neon_masked_sum_count_f32`.
/// Uses `f32x4(mask_byte != 0)` per lane for the mask conversion.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_masked_sum_count_f32(x: &[f32], mask: &[u8]) -> (f32, u32) {
    use core::arch::wasm32::{
        f32x4, f32x4_add, f32x4_extract_lane, f32x4_mul, f32x4_splat, v128_load,
    };
    unsafe {
        let zero = f32x4_splat(0.0);
        let mut acc0 = zero;
        let mut acc1 = zero;
        let mut acc2 = zero;
        let mut acc3 = zero;
        let mut count: u32 = 0;
        let mut i = 0;
        let len = x.len();
        let chunks4 = len / 16;

        for _ in 0..chunks4 {
            let m0 = mask_f32x4_wasm(mask, i);
            let m1 = mask_f32x4_wasm(mask, i + 4);
            let m2 = mask_f32x4_wasm(mask, i + 8);
            let m3 = mask_f32x4_wasm(mask, i + 12);
            let x0 = v128_load(x.as_ptr().add(i).cast());
            let x1 = v128_load(x.as_ptr().add(i + 4).cast());
            let x2 = v128_load(x.as_ptr().add(i + 8).cast());
            let x3 = v128_load(x.as_ptr().add(i + 12).cast());
            acc0 = f32x4_add(acc0, f32x4_mul(x0, m0));
            acc1 = f32x4_add(acc1, f32x4_mul(x1, m1));
            acc2 = f32x4_add(acc2, f32x4_mul(x2, m2));
            acc3 = f32x4_add(acc3, f32x4_mul(x3, m3));
            count += mask_count_4_wasm(mask, i)
                + mask_count_4_wasm(mask, i + 4)
                + mask_count_4_wasm(mask, i + 8)
                + mask_count_4_wasm(mask, i + 12);
            i += 16;
        }

        let s = f32x4_add(f32x4_add(acc0, acc1), f32x4_add(acc2, acc3));
        let mut sum = f32x4_extract_lane::<0>(s)
            + f32x4_extract_lane::<1>(s)
            + f32x4_extract_lane::<2>(s)
            + f32x4_extract_lane::<3>(s);

        let remaining = (len - i) / 4;
        let mut acc_rem = zero;
        for _ in 0..remaining {
            let m = mask_f32x4_wasm(mask, i);
            let xv = v128_load(x.as_ptr().add(i).cast());
            acc_rem = f32x4_add(acc_rem, f32x4_mul(xv, m));
            count += mask_count_4_wasm(mask, i);
            i += 4;
        }
        sum += f32x4_extract_lane::<0>(acc_rem)
            + f32x4_extract_lane::<1>(acc_rem)
            + f32x4_extract_lane::<2>(acc_rem)
            + f32x4_extract_lane::<3>(acc_rem);

        while i < len {
            let m = u32::from(*mask.get_unchecked(i) != 0);
            sum += *x.get_unchecked(i) * (m as f32);
            count += m;
            i += 1;
        }
        (sum, count)
    }
}

/// Helper: build a wasm32 f32x4 mask (0.0/1.0 per lane) from `mask[i..i+4]`.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline(always)]
unsafe fn mask_f32x4_wasm(mask: &[u8], i: usize) -> core::arch::wasm32::v128 {
    use core::arch::wasm32::f32x4;
    unsafe {
        f32x4(
            ((*mask.get_unchecked(i) != 0) as u8) as f32,
            ((*mask.get_unchecked(i + 1) != 0) as u8) as f32,
            ((*mask.get_unchecked(i + 2) != 0) as u8) as f32,
            ((*mask.get_unchecked(i + 3) != 0) as u8) as f32,
        )
    }
}

/// Helper: count non-zero mask values in `mask[i..i+4]` (wasm32 backend).
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline(always)]
unsafe fn mask_count_4_wasm(mask: &[u8], i: usize) -> u32 {
    unsafe {
        u32::from(*mask.get_unchecked(i) != 0)
            + u32::from(*mask.get_unchecked(i + 1) != 0)
            + u32::from(*mask.get_unchecked(i + 2) != 0)
            + u32::from(*mask.get_unchecked(i + 3) != 0)
    }
}

/// WASM SIMD128 in-place add. Mirrors `neon_add_inplace`.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_add_inplace(dst: &mut [f32], src: &[f32]) {
    use core::arch::wasm32::{f32x4_add, v128_load, v128_store};

    unsafe {
        let mut i = 0;
        let chunks = dst.len() / 4;

        for _ in 0..chunks {
            let vd = v128_load(dst.as_ptr().add(i).cast());
            let vs = v128_load(src.as_ptr().add(i).cast());
            let result = f32x4_add(vd, vs);
            v128_store(dst.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < dst.len() {
            *dst.get_unchecked_mut(i) += *src.get_unchecked(i);
            i += 1;
        }
    }
}

/// WASM SIMD128 zip add. Mirrors `neon_add_into`.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_add_into(dst: &mut [f32], a: &[f32], b: &[f32]) {
    use core::arch::wasm32::{f32x4_add, v128_load, v128_store};

    unsafe {
        let mut i = 0;
        let chunks = dst.len() / 4;

        for _ in 0..chunks {
            let va = v128_load(a.as_ptr().add(i).cast());
            let vb = v128_load(b.as_ptr().add(i).cast());
            let result = f32x4_add(va, vb);
            v128_store(dst.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < dst.len() {
            *dst.get_unchecked_mut(i) = *a.get_unchecked(i) + *b.get_unchecked(i);
            i += 1;
        }
    }
}

/// WASM SIMD128 max reduction. Mirrors `neon_max_f32` (4 independent
/// vector-max accumulators = 16 elements per outer iter). Lane reduce via
/// `f32::max` replaces NEON `vmaxvq_f32` (no single horizontal-max instr).
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_max_f32(x: &[f32]) -> f32 {
    use core::arch::wasm32::{f32x4_extract_lane, f32x4_max, v128_load};

    unsafe {
        let len = x.len();
        let chunks = len / 4;
        if chunks == 0 {
            let mut max = x[0];
            for j in 1..len {
                let v = *x.get_unchecked(j);
                if v > max {
                    max = v;
                }
            }
            return max;
        }

        // 4 independent vector-max accumulators to hide the max-op latency.
        // max is associative + commutative, so this is bit-identical to serial.
        let mut vmax0 = v128_load(x.as_ptr().cast());
        let mut vmax1 = vmax0;
        let mut vmax2 = vmax0;
        let mut vmax3 = vmax0;
        let mut i = 0;
        let chunks4 = len / 16;
        for _ in 0..chunks4 {
            vmax0 = f32x4_max(vmax0, v128_load(x.as_ptr().add(i).cast()));
            vmax1 = f32x4_max(vmax1, v128_load(x.as_ptr().add(i + 4).cast()));
            vmax2 = f32x4_max(vmax2, v128_load(x.as_ptr().add(i + 8).cast()));
            vmax3 = f32x4_max(vmax3, v128_load(x.as_ptr().add(i + 12).cast()));
            i += 16;
        }
        let mut vmax = f32x4_max(f32x4_max(vmax0, vmax1), f32x4_max(vmax2, vmax3));
        // Remaining 4-element chunks
        while i + 4 <= len {
            vmax = f32x4_max(vmax, v128_load(x.as_ptr().add(i).cast()));
            i += 4;
        }

        // Horizontal max of 4 lanes (NEON uses `vmaxvq_f32`; replicate via
        // lane extraction + `f32::max`, matching the scalar reference's
        // `max.max(v)` reduce semantics).
        let mut max = f32x4_extract_lane::<0>(vmax)
            .max(f32x4_extract_lane::<1>(vmax))
            .max(f32x4_extract_lane::<2>(vmax))
            .max(f32x4_extract_lane::<3>(vmax));

        // Handle tail
        while i < len {
            let v = *x.get_unchecked(i);
            if v > max {
                max = v;
            }
            i += 1;
        }
        max
    }
}

/// WASM SIMD128 fused decay-write: `dst = dst*decay + src*write`.
/// Mirrors `neon_fused_decay_write`. NEON uses one `vfmaq_f32`; WASM has no
/// FMA intrinsic so this is `f32x4_mul` + `f32x4_add` (1 ULP acceptable vs
/// the FMA path — the engine JIT may fuse mul→add when profitable).
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_fused_decay_write(dst: &mut [f32], decay: f32, src: &[f32], write: f32) {
    use core::arch::wasm32::{f32x4_add, f32x4_mul, f32x4_splat, v128_load, v128_store};

    unsafe {
        let vd_decay = f32x4_splat(decay);
        let vd_write = f32x4_splat(write);
        let mut i = 0;
        let chunks = dst.len() / 4;

        for _ in 0..chunks {
            let vdst = v128_load(dst.as_ptr().add(i).cast());
            let vsrc = v128_load(src.as_ptr().add(i).cast());
            // dst*decay + src*write (NEON: single FMA; WASM: mul→add).
            let result = f32x4_add(f32x4_mul(vdst, vd_decay), f32x4_mul(vsrc, vd_write));
            v128_store(dst.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < dst.len() {
            *dst.get_unchecked_mut(i) =
                decay * *dst.get_unchecked(i) + write * *src.get_unchecked(i);
            i += 1;
        }
    }
}

/// WASM SIMD128 fused scale+multiply: `x = gamma * x * scale`.
/// Mirrors `neon_scale_mul_inplace` — pure 2-multiply chain, no FMA involved.
#[cfg(all(target_arch = "wasm32", target_feature = "simd128"))]
#[inline]
unsafe fn wasm32_simd128_scale_mul_inplace(x: &mut [f32], gamma: &[f32], scale: f32) {
    use core::arch::wasm32::{f32x4_mul, f32x4_splat, v128_load, v128_store};

    unsafe {
        let vs = f32x4_splat(scale);
        let mut i = 0;
        let chunks = x.len() / 4;

        for _ in 0..chunks {
            let vx = v128_load(x.as_ptr().add(i).cast());
            let vg = v128_load(gamma.as_ptr().add(i).cast());
            let result = f32x4_mul(vg, f32x4_mul(vx, vs));
            v128_store(x.as_mut_ptr().add(i).cast(), result);
            i += 4;
        }

        while i < x.len() {
            *x.get_unchecked_mut(i) = *gamma.get_unchecked(i) * *x.get_unchecked(i) * scale;
            i += 1;
        }
    }
}