Convert Dot Multiply from C2H to ???

I have the following simple vector dot multiply as a C2H accelerator.

For some situations (but not all) regular NIOS running 50MHz on a 2C8 is fast enough running in code.

I want to implement this as something supported by Qsys and newer Quartus.

Options? Special instruction in NIOS? User component in Qsys? Something else?

I have constructed signal processing accelerators outside of NIOS using read and write masters, but would like to avoid that effort here.

Seems likely this function has been covered before.

// Multiply data vector with polyphase filter
int DotMpy(int* __restrict__ r, int* __restrict__ p, alt_u16 PolySel)
{
   # pragma altera_accelerate connect_variable DotMpy/r to sdram
   # pragma altera_accelerate connect_variable DotMpy/r to onchip_SRAM
   # pragma altera_accelerate connect_variable DotMpy/p to onchip_SRAM
    long long SumVal = 0;
    int k = 20;
    do {
         SumVal += (long long)*r++ * (long long)*p;
         if (PolySel&0x100) (p--); else (p++);
    } while (--k);
    return (int)(SumVal >> 16);
}