Min/Max reduction example

LdsMinMax.hlsl

groupshared float ldsMin[64];
groupshared float ldsMax[64];

void LdsMinMax(uint Idx, uint Ofs)
{
    [branch] if (Idx < Ofs)
    {
        ldsMin[Idx] = min(ldsMin[Idx], ldsMin[Idx + Ofs]);
        ldsMax[Idx] = max(ldsMax[Idx], ldsMax[Idx + Ofs]);
    }
}

/* Avoid storing data to LDS if it will be read in a next step ? */
float2 LdsMinMax64_Reduce(float2 MinMax, uint LocalId)
{
    ldsMin[LocalId] = MinMax.x;
    ldsMax[LocalId] = MinMax.y;
    LdsMinMax(LocalId, 32);
    LdsMinMax(LocalId, 16);
    LdsMinMax(LocalId,  8);
    LdsMinMax(LocalId,  4);
    LdsMinMax(LocalId,  2);
    /*
    LdsMinMax(LocalId,  1);
    return float2(ldsMin[0], ldsMax[0]);
    /*/
    return float2(min(ldsMin[0], ldsMin[1]), max(ldsMax[0], ldsMax[1]));
    //*/
}

groupshared uint ldsMinAtomic;
groupshared uint ldsMaxAtomic;

float2 LdsMinMax64_Atomic(float2 MinMax, uint LocalId)
{
    [branch] if (LocalId == 0)
    {
        ldsMinAtomic = 0;
        ldsMaxAtomic = 0;
    }
    InterlockedMax(ldsMinAtomic, asuint(MinMax.x));
    InterlockedMax(ldsMaxAtomic, asuint(MinMax.y));
    return asfloat(uint2(ldsMinAtomic, ldsMaxAtomic));
}