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to Circular Buffer in the D Track

Published at Sep 24 2018 · 0 comments
Instructions
Test suite
Solution

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3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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 D page on exercism.io. 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. Create just enough structure by declaring namespaces, functions, classes, etc., 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, uncomment the next test by moving the following line past the next test.

static if (all_tests_enabled)

This may result in compile errors as new constructs may be invoked that you haven't yet declared or defined. Again, fix the compile errors minimally to get a failing test, then change the code minimally to pass the test, refactor your implementation for readability and expressiveness and then go on to the next test.

Try to use standard D facilities in preference to writing your own low-level algorithms or facilities by hand. DRefLanguage and DReference are references to the D language and D standard library.

Source

Wikipedia 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.

circular_buffer.d

module circular;

unittest
{
import std.exception : assertThrown;

immutable int allTestsEnabled = 0;

// test read empty buffer
{
	auto myBuffer = new Buffer!(int)(1UL);
	assertThrown(myBuffer.pop(), "Empty buffer should throw exception if popped!");
}

static if (allTestsEnabled)
{

// test write and read back one item
{
	auto myBuffer = new Buffer!(char)(1);
	myBuffer.push('1');
	assert(myBuffer.pop() == '1');
}

// test write and read back multiple items
{
	auto myBuffer =  new Buffer!(char)(2);
	myBuffer.push('1');
	myBuffer.push('2');
	assert(myBuffer.pop() == '1');
	assert(myBuffer.pop() == '2');
}

// test clearing the buffer
{
	auto myBuffer = new Buffer!(char)(3);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');

	myBuffer.clear();
	assertThrown(myBuffer.pop(), "Empty buffer should throw exception if popped!");
}

// test alternate write and read
{
	auto myBuffer = new Buffer!(char)(2);
	myBuffer.push('1');
	assert(myBuffer.pop() == '1');
	myBuffer.push('2');
	assert(myBuffer.pop() == '2');
}

// test read back oldest item
{
	auto myBuffer = new Buffer!(char)(4);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.pop();
	myBuffer.push('3');
	myBuffer.pop();

	assert(myBuffer.pop() == '3');
}

// test write buffer
{
	auto myBuffer = new Buffer!(char)(3);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');

	assertThrown(myBuffer.push('4'), "Full buffer should throw exception if new element pushed!");
}

// test forcePush full buffer
{
	auto myBuffer = new Buffer!(char)(3);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');

	myBuffer.forcePush('A');
	assert(myBuffer.pop() == '2');
	assert(myBuffer.pop() == '3');
	assert(myBuffer.pop() == 'A');
}

// test forcePush non-full buffer
{
	auto myBuffer = new Buffer!(int)(2);
	myBuffer.forcePush(1000);
	myBuffer.forcePush(2000);

	assert(myBuffer.pop() == 1000);
	assert(myBuffer.pop() == 2000);
}

// test alternate read and forcePush
{
	auto myBuffer = new Buffer!(char)(5);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');
	myBuffer.pop();
	myBuffer.pop();

	myBuffer.push('4');
	myBuffer.pop();

	myBuffer.push('5');
	myBuffer.push('6');
	myBuffer.push('7');
	myBuffer.push('8');
	myBuffer.forcePush('A');
	myBuffer.forcePush('B');

	assert(myBuffer.pop() == '6');
	assert(myBuffer.pop() == '7');
	assert(myBuffer.pop() == '8');
	assert(myBuffer.pop() == 'A');
	assert(myBuffer.pop() == 'B');
	assertThrown(myBuffer.pop(), "Empty buffer should throw exception if popped!");
}

}

}
module circular;

class Buffer(T) {
  int start = 0;
  int end = 0;
  int size;
  int count;
  T[] back;
  this(int s) {
    back = new T[s];
    size = s;
  }

  void shiftEnd(int i) {
    end += i;
    if (end <= 0) {
      end = size - end;
    } else if (end >= size) {
      end = end - size;
    }
  }

  void shiftStart(int i) {
    start += i;
    if (start <= 0) {
      start = size - start;
    } else if (start >= size) {
      start = start - size;
    }
  }

  T pop() {
    if (count <= 0) {
        throw new Exception("Empty buffer");
    } else {
      shiftStart(1);
      count--;
      return back[start];
    }
  }
  void push(T item) {
    if (count < size) {
      shiftEnd(1);
      count++;
      back[end] = item;
    } else {
      throw new Exception("Full buffer");
    }
  }
  void forcePush(T item) {
    shiftEnd(1);
    back[end] = item;
    if (count < size) {
      count++;
    } else {
      shiftStart(1);
    }
  }
  void clear() {
    back = new T[size];
    count = 0;
    end = 0;
  }
}

unittest
{
import std.exception : assertThrown;

immutable int allTestsEnabled = 1;

// test read empty buffer
{
	auto myBuffer = new Buffer!(int)(1UL);
	assertThrown(myBuffer.pop(), "Empty buffer should throw exception if popped!");
}

static if (allTestsEnabled)
{

// test write and read back one item
{
	auto myBuffer = new Buffer!(char)(1);
	myBuffer.push('1');
	assert(myBuffer.pop() == '1');
}

// test write and read back multiple items
{
	auto myBuffer =  new Buffer!(char)(2);
	myBuffer.push('1');
	myBuffer.push('2');
	assert(myBuffer.pop() == '1');
	assert(myBuffer.pop() == '2');
}

// test clearing the buffer
{
	auto myBuffer = new Buffer!(char)(3);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');

	myBuffer.clear();
	assertThrown(myBuffer.pop(), "Empty buffer should throw exception if popped!");
}

// test alternate write and read
{
	auto myBuffer = new Buffer!(char)(2);
	myBuffer.push('1');
	assert(myBuffer.pop() == '1');
	myBuffer.push('2');
	assert(myBuffer.pop() == '2');
}

// test read back oldest item
{
	auto myBuffer = new Buffer!(char)(4);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.pop();
	myBuffer.push('3');
	myBuffer.pop();

	assert(myBuffer.pop() == '3');
}

// test write buffer
{
	auto myBuffer = new Buffer!(char)(3);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');

	assertThrown(myBuffer.push('4'), "Full buffer should throw exception if new element pushed!");
}

// test forcePush full buffer
{
	auto myBuffer = new Buffer!(char)(3);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');

	myBuffer.forcePush('A');
	assert(myBuffer.pop() == '2');
	assert(myBuffer.pop() == '3');
	assert(myBuffer.pop() == 'A');
}

// test forcePush non-full buffer
{
	auto myBuffer = new Buffer!(int)(2);
	myBuffer.forcePush(1000);
	myBuffer.forcePush(2000);

	assert(myBuffer.pop() == 1000);
	assert(myBuffer.pop() == 2000);
}

// test alternate read and forcePush
{
	auto myBuffer = new Buffer!(char)(5);
	myBuffer.push('1');
	myBuffer.push('2');
	myBuffer.push('3');
	myBuffer.pop();
	myBuffer.pop();

	myBuffer.push('4');
	myBuffer.pop();

	myBuffer.push('5');
	myBuffer.push('6');
	myBuffer.push('7');
	myBuffer.push('8');
	myBuffer.forcePush('A');
	myBuffer.forcePush('B');

	assert(myBuffer.pop() == '6');
	assert(myBuffer.pop() == '7');
	assert(myBuffer.pop() == '8');
	assert(myBuffer.pop() == 'A');
	assert(myBuffer.pop() == 'B');
	assertThrown(myBuffer.pop(), "Empty buffer should throw exception if popped!");
}

}

}

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