C: circular buffer

c/circular-buffer/README.md

@@ -0,0 +1,89 @@
+# Circular Buffer
+
+A circular buffer, cyclic buffer or ring buffer is a data structure that
+uses a single, fixed-size buffer as if it were connected end-to-end.
+
+A circular buffer first starts empty and of some predefined length. For
+example, this is a 7-element buffer:
+
+    [ ][ ][ ][ ][ ][ ][ ]
+
+Assume that a 1 is written into the middle of the buffer (exact starting
+location does not matter in a circular buffer):
+
+    [ ][ ][ ][1][ ][ ][ ]
+
+Then assume that two more elements are added — 2 & 3 — which get
+appended after the 1:
+
+    [ ][ ][ ][1][2][3][ ]
+
+If two elements are then removed from the buffer, the oldest values
+inside the buffer are removed. The two elements removed, in this case,
+are 1 & 2, leaving the buffer with just a 3:
+
+    [ ][ ][ ][ ][ ][3][ ]
+
+If the buffer has 7 elements then it is completely full:
+
+    [6][7][8][9][3][4][5]
+
+When the buffer is full an error will be raised, alerting the client
+that further writes are blocked until a slot becomes free.
+
+When the buffer is full, the client can opt to overwrite the oldest
+data with a forced write. In this case, two more elements — A & B —
+are added and they overwrite the 3 & 4:
+
+    [6][7][8][9][A][B][5]
+
+3 & 4 have been replaced by A & B making 5 now the oldest data in the
+buffer. Finally, if two elements are removed then what would be
+returned is 5 & 6 yielding the buffer:
+
+    [ ][7][8][9][A][B][ ]
+
+Because there is space available, if the client again uses overwrite
+to store C & D then the space where 5 & 6 were stored previously will
+be used not the location of 7 & 8. 7 is still the oldest element and
+the buffer is once again full.
+
+    [D][7][8][9][A][B][C]
+
+## Getting Started
+
+Make sure you have read the "Guides" section of the
+[C track][c-track] on the Exercism site. This covers
+the basic information on setting up the development environment expected
+by the exercises.
+
+## Passing the Tests
+
+Get the first test compiling, linking and passing by following the [three
+rules of test-driven development][3-tdd-rules].
+
+The included makefile can be used to create and run the tests using the `test`
+task.
+
+    make test
+
+Create just the functions you need to satisfy any compiler errors and get the
+test to fail. Then write just enough code to get the test to pass. Once you've
+done that, move onto the next test.
+
+As you progress through the tests, take the time to refactor your
+implementation for readability and expressiveness and then go on to the next
+test.
+
+Try to use standard C99 facilities in preference to writing your own
+low-level algorithms or facilities by hand.
+
+## Source
+
+Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+
+[c-track]: https://exercism.io/my/tracks/c
+[3-tdd-rules]: http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd