Function hsum256

nodedb-vector/src/distance/simd/avx2.rs:106–116

(v: std::arch::x86_64::__m256)

/// Horizontal sum of 8 × f32 in a __m256.
#[target_feature(enable = "avx2")]
unsafe fn hsum256(v: std::arch::x86_64::__m256) -> f32 {
    use std::arch::x86_64::*;
    let hi = _mm256_extractf128_ps(v, 1);
    let lo = _mm256_castps256_ps128(v);
    let sum128 = _mm_add_ps(lo, hi);
    let shuf = _mm_movehdup_ps(sum128);
    let sums = _mm_add_ps(sum128, shuf);
    let shuf2 = _mm_movehl_ps(sums, sums);
    let sums2 = _mm_add_ss(sums, shuf2);
    _mm_cvtss_f32(sums2)
}