compute_cube_index()

uint32_t MayaFlux::Kinesis::compute_cube_index ( const float *  v, float  iso  )

inlinenoexcept

Definition at line 15 of file MarchingCube.cpp.

{
#ifdef MAYAFLUX_ARCH_X64
    const __m256 vals = _mm256_loadu_ps(v);
    const __m256 threshold = _mm256_set1_ps(iso);
    const __m256 cmp = _mm256_cmp_ps(vals, threshold, _CMP_LT_OS);
    return static_cast<uint32_t>(_mm256_movemask_ps(cmp));
#elif defined(MAYAFLUX_ARCH_ARM64)
    const float32x4_t lo = vld1q_f32(v);
    const float32x4_t hi = vld1q_f32(v + 4);
    const float32x4_t thresh = vdupq_n_f32(iso);
 
    // vcltq_f32 -> 0xFFFFFFFF per lane where v[i] < iso, 0x00000000 otherwise.
    // Shift each lane right by (31 - bit_position) to land the set bit at the
    // correct position in the final scalar, then sum across lanes.
    const uint32x4_t lo_mask = vcltq_f32(lo, thresh);
    const uint32x4_t hi_mask = vcltq_f32(hi, thresh);
 
    // Isolate bit 0 of each lane (the sign bit after the comparison saturates).
    // vshrq_n_u32 by 31 collapses each 0xFFFFFFFF to 1 and 0x00000000 to 0.
    alignas(16) static const uint32_t k_lo_shifts[4] = { 31, 30, 29, 28 };
    alignas(16) static const uint32_t k_hi_shifts[4] = { 27, 26, 25, 24 };
 
    const uint32x4_t lo_bits = vshlq_u32(vshrq_n_u32(lo_mask, 31),
        vld1q_s32(reinterpret_cast<const int32_t*>(k_lo_shifts)));
    const uint32x4_t hi_bits = vshlq_u32(vshrq_n_u32(hi_mask, 31),
        vld1q_s32(reinterpret_cast<const int32_t*>(k_hi_shifts)));
 
    const uint32x4_t combined = vorrq_u32(lo_bits, hi_bits);
    return vaddvq_u32(combined);
#else
    uint32_t idx = 0;
    idx |= static_cast<uint32_t>(v[0] < iso) << 0;
    idx |= static_cast<uint32_t>(v[1] < iso) << 1;
    idx |= static_cast<uint32_t>(v[2] < iso) << 2;
    idx |= static_cast<uint32_t>(v[3] < iso) << 3;
    idx |= static_cast<uint32_t>(v[4] < iso) << 4;
    idx |= static_cast<uint32_t>(v[5] < iso) << 5;
    idx |= static_cast<uint32_t>(v[6] < iso) << 6;
    idx |= static_cast<uint32_t>(v[7] < iso) << 7;
    return idx;
#endif
}

References threshold().

Referenced by generate_sdf_mesh().

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