// DS4 Metal concat kernel used by the graph.

struct ds4_metal_args_concat {
    int32_t  ne00;
    int32_t  ne01;
    int32_t  ne02;
    int32_t  ne03;
    uint64_t nb00;
    uint64_t nb01;
    uint64_t nb02;
    uint64_t nb03;
    int32_t  ne10;
    int32_t  ne11;
    int32_t  ne12;
    int32_t  ne13;
    uint64_t nb10;
    uint64_t nb11;
    uint64_t nb12;
    uint64_t nb13;
    int32_t  ne0;
    int32_t  ne1;
    int32_t  ne2;
    int32_t  ne3;
    uint64_t nb0;
    uint64_t nb1;
    uint64_t nb2;
    uint64_t nb3;
    int32_t  dim;
};

// Concatenates two float tensors along one dimension. In DS4 this is a graph
// utility for assembling attention inputs with exactly the same tensor layout
// expected by the downstream kernels.
kernel void kernel_concat(
        constant ds4_metal_args_concat & args,
        device  const char * src0,
        device  const char * src1,
        device        char * dst,
        uint3   tgpig[[threadgroup_position_in_grid]],
        ushort3 tpitg[[thread_position_in_threadgroup]],
        ushort3   ntg[[threads_per_threadgroup]]) {
    const int i3 = tgpig.z;
    const int i2 = tgpig.y;
    const int i1 = tgpig.x;

    int o[4] = {0, 0, 0, 0};
    o[args.dim] = args.dim == 0 ? args.ne00 : (args.dim == 1 ? args.ne01 : (args.dim == 2 ? args.ne02 : args.ne03));

    device const float * x;

    for (int i0 = tpitg.x; i0 < args.ne0; i0 += ntg.x) {
        if (i0 < args.ne00 && i1 < args.ne01 && i2 < args.ne02 && i3 < args.ne03) {
            x = (device const float *)(src0 + (i3       )*args.nb03 + (i2       )*args.nb02 + (i1       )*args.nb01 + (i0       )*args.nb00);
        } else {
            x = (device const float *)(src1 + (i3 - o[3])*args.nb13 + (i2 - o[2])*args.nb12 + (i1 - o[1])*args.nb11 + (i0 - o[0])*args.nb10);
        }

        device float * y = (device float *)(dst + i3*args.nb3 + i2*args.nb2 + i1*args.nb1 + i0*args.nb0);

        *y = *x;
    }
}