Macro simd_4acc_l2_loop 

macro_rules! simd_4acc_l2_loop {
    ($a_ptr:expr, $b_ptr:expr, $end:expr,
     $zero:expr, $load:ident, $sub:ident, $fmadd:ident, $add:ident, $lane:expr) => { ... };
}

4-accumulator unrolled SIMD loop for squared L2 distance.

Same structure as simd_4acc_dot_loop! but computes sum((a-b)²) instead of sum(a·b). Requires an additional $sub intrinsic.

Safety

Same requirements as simd_4acc_dot_loop!.