8ssedt/include/simd_compare.hpp

//
//  simd_compare.hpp
//  8ssedt
//
//  Created by Pujun Lun on 4/21/18.
//  Copyright © 2018 Pujun Lun. All rights reserved.
//

#ifndef simd_compare_hpp
#define simd_compare_hpp

#include <immintrin.h>
#include "avoid_edge_check.hpp"

class SimdCompare : public AvoidEdgeCheck {
protected:
    void GenerateSDF(Grid &g) override;
    inline Point GroupCompare(Grid &g, Point other, int x, int y, const __m256i& offsets) {
        Point self = Get(g, x, y);
        
        /* Point other = Get( g, x+offsetx, y+offsety ); */
        int *offsetsPtr = (int *)&offsets;
        Point pn[4] = {
            other,
            Get(g, x + offsetsPtr[1], y + offsetsPtr[5]),
            Get(g, x + offsetsPtr[2], y + offsetsPtr[6]),
            Get(g, x + offsetsPtr[3], y + offsetsPtr[7]),
        };
        
        /* other.dx += offsetx; other.dy += offsety; */
        __m256i *pnPtr = (__m256i *)pn;
        // x0, y0, x1, y1, x2, y2, x3, y3 -> x0, x1, x2, x3, y0, y1, y2, y3
        static const __m256i mask = _mm256_setr_epi32(0, 2, 4, 6, 1, 3, 5, 7);
        __m256i vecCoords = _mm256_permutevar8x32_epi32(*pnPtr, mask);
        vecCoords = _mm256_add_epi32(vecCoords, offsets);
        
        /* other.DistSq() */
        int *coordsPtr = (int *)&vecCoords;
        // note that _mm256_mul_epi32 only applies on the lower 128 bits
        __m256i vecPermuted = _mm256_permute2x128_si256(vecCoords , vecCoords, 1);
        __m256i vecSqrDists = _mm256_add_epi64(_mm256_mul_epi32(vecCoords, vecCoords),
                                               _mm256_mul_epi32(vecPermuted, vecPermuted));
        
        /* if (other.DistSq() < p.DistSq()) p = other; */
        int64_t prevDist = self.DistSq(), index = -1;
        for (int i = 0; i < 4; ++i) {
            int64_t dist = *((int64_t *)&vecSqrDists + i);
            if (dist < prevDist) {
                prevDist = dist;
                index = i;
            }
        }
        if (index != -1) {
            other = { coordsPtr[index], coordsPtr[index + 4] };
            Put(g, x, y, other);
            return other;
        } else {
            return self;
        }
    }
};

#endif /* simd_compare_hpp */