P3 RGB pixel panel

During my test for this LED board, I tested a driver using setPixel in javascript.
At the end it turns out, that this is faster than a converting step (see above)
And it does not waste more memory.
Even being faster than expected, I would like to add setPixel for LED Panels in C. These would be only a few lines, but I've no idea, where and how to add.

me.setPixel = function(x,y,col){
    var adr = ((y & 0xf) << 6) + x; 
    if(y>15) ledBuf[adr] = (ledBuf[adr] & 0xf8) + col;
    else ledBuf[adr] = (ledBuf[adr] & 0xc7) + (col<<3);
  };