void main() {
    // NB: hack to make compatible with AMD GPUs that have a subgroup size of 64
    if (gl_SubgroupInvocationID > 31)
        return;

    const uint nb = uint(pcs.ne00/BLOCKS_IN_QUANT);

    const uint r0 = gl_WorkGroupID.x;
    const uint r1 = gl_WorkGroupID.y;
    const uint im = gl_WorkGroupID.z;

    const uint first_row = (r0 * gl_NumSubgroups + gl_SubgroupID) * N_ROWS;

    const uint i12 = im%pcs.ne12;
    const uint i13 = im/pcs.ne12;

    // pointers to src0 rows
    uint ax[N_ROWS];
    for (int row = 0; row < N_ROWS; ++row) {
        const uint offset0 = (first_row + row)*(pcs.nb01/SIZE_OF_BLOCK) + (i12/pcs.r2)*(pcs.nb02/SIZE_OF_BLOCK) + (i13/pcs.r3)*(pcs.nb03/SIZE_OF_BLOCK);

        ax[row] = offset0 + pcs.inAOff;
    }

    const uint y = (r1*pcs.nb11 + i12*pcs.nb12 + i13*pcs.nb13) / 4 + pcs.inBOff;

    float sumf[N_ROWS] = {0.0f, 0.0f, 0.0f, 0.0f};

    const uint ix = gl_SubgroupInvocationID/2;
    const uint il = (BLOCKS_IN_QUANT/4)*(gl_SubgroupInvocationID%2);

    uint yb = y + ix * BLOCKS_IN_QUANT + il;

    //debugPrintfEXT("gl_NumSubgroups=%d, gl_SubgroupID=%d, gl_SubgroupInvocationID=%d, glSubgroupSize=%d, gl_WorkGroupSize.x=%d, gl_WorkGroupSize.y=%d, gl_WorkGroupSize.z=%d\n",
    //    gl_NumSubgroups, gl_SubgroupID, gl_SubgroupInvocationID, gl_SubgroupSize,
    //    gl_WorkGroupSize.x, gl_WorkGroupSize.y, gl_WorkGroupSize.z);

    for (uint ib = ix; ib < nb; ib += 16) {
        for (int row = 0; row < N_ROWS; row++) {
            sumf[row] += block_q_n_dot_y(ax[row] + ib, yb, il);
        }

        yb += BLOCKS_IN_QUANT * 16;
    }

    for (int row = 0; row < N_ROWS; ++row) {
        const float tot = subgroupAdd(sumf[row]);
        if (first_row + row < pcs.ne01 && subgroupElect()) {
            out_[r1*pcs.ne0 + im*pcs.ne0*pcs.ne1 + first_row + row + pcs.outOff] = tot;
        }
    }
}