#Franken-Buffer

A combination link-list and ring-buffer for situations where your memory is limited and fragmented.

The inspiration to write this came from using a PIC where I couldn't allocate a large enough single memory block to buffer data coming in from a high-speed serial link. Due to time constraints of the application, this code does not use a single branching statement (if/switch) when adding data to the buffer. Each write increments the ring buffer and the link list simultaneously.

Speed savings are made with the ring buffer by masking in the index to ensure it only counts from 1 to any 2ⁿ value. The link list allows your buffer to be the size of n times an arbitrary value. A double ring-buffer could have been used but this had too many limitations in the total size the buffer could occupy.

#Usage This is still currently a little dirty.

There are two main declarations which first need setup: FKN_OUTER_BUFF_SIZE, which can be any value and FKN_INNER_BUFF_SIZE which must be of 2ⁿ (ie. 8, 16, 32).

Next, you need to declare your outer buffer. This is a pseudo-link-list. I say pseudo as you can't add/remove nodes, but still uses the concept of holding a pointer to the next entry in it's own structure. The reason for this will become apparent if you look at the implementation of the fkn_buffer_add function.

To use the buffer you also need to declare a pointer of type FKNBUFFER. This is your route in and out of the buffer and is returned by fkn_buffer_setup

Adding data is performed through fkn_buffer_add which places a value in the next buffer space. Retrieving data is performed using fkn_get_data which takes as a parameter an arbitrary location in the buffer. The add routine is designed to be blindingly fast, the get routine is not. Lastly, there is a function fkn_buffer_clean which sets all the values in the buffer to zero.

#Example

  int i; 
  struct FKNBUFFER *outer;
  struct FKNBUFFER buffer_raw[FKN_OUTER_BUFF_SIZE];

  outer = fkn_buffer_setup(buffer_raw);
  fkn_buffer_clear(outer);

  for (i=0; i<FKN_BUFF_SIZE; i++){
    fkn_buffer_add(&outer, i); // Add 0 to 79
  }

  for (i=0; i<FKN_BUFF_SIZE; i++){
    printf("i=%d \t %d\n", i, fkn_buffer_get(outer, i)); // Read out 0 to 79
  }

In this example it would be possible to use malloc instead of declaring buffer_raw as shown, however for readability this has been ommited.

#Requirements

The setup function currently requires malloc in order to give itself the space it requires to operate.