Fixing & optimizing FixedDeque & CircularBuffer

Fix #223

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Fixing `Float64Vector` TS exports (@atombrenner).
 * Improving performance of `FixedDeque` `#.push` & `#.pop` methods (@jerome-benoit).
+* Fixing some `FixedDeque` & `CircularBuffer` methods.
 
 ## 0.39.7
 

circular-buffer.js

@@ -45,15 +45,24 @@ if (typeof Symbol !== 'undefined')
  * @return {number}      - Returns the new size of the buffer.
  */
 CircularBuffer.prototype.push = function(item) {
-  var index = (this.start + this.size) % this.capacity;
+  var index = this.start + this.size;
+
+  if (index >= this.capacity)
+    index -= this.capacity;
 
   this.items[index] = item;
 
   // Overwriting?
   if (this.size === this.capacity) {
-
-    // If start is at the end, we wrap around the buffer
-    this.start = (index + 1) % this.capacity;
+    index++;
+
+    // Wrapping around?
+    if (index >= this.capacity) {
+      this.start = 0;
+    }
+    else {
+      this.start = index;
+    }
 
     return this.size;
   }

fixed-deque.js

@@ -88,12 +88,12 @@ FixedDeque.prototype.pop = function() {
   if (this.size === 0)
     return;
 
-  var index = this.start + this.size - 1;
+  this.size--;
 
-  if (index > this.capacity)
-    index -= this.capacity;
+  var index = this.start + this.size;
 
-  this.size--;
+  if (index >= this.capacity)
+    index -= this.capacity;
 
   return this.items[index];
 };
@@ -141,7 +141,7 @@ FixedDeque.prototype.peekLast = function() {
 
   var index = this.start + this.size - 1;
 
-  if (index > this.capacity)
+  if (index >= this.capacity)
     index -= this.capacity;
 
   return this.items[index];
@@ -154,12 +154,12 @@ FixedDeque.prototype.peekLast = function() {
  * @return {any}
  */
 FixedDeque.prototype.get = function(index) {
-  if (this.size === 0)
+  if (this.size === 0 || index >= this.capacity)
     return;
 
   index = this.start + index;
 
-  if (index > this.capacity)
+  if (index >= this.capacity)
     index -= this.capacity;
 
   return this.items[index];

test/circular-buffer.js

@@ -126,6 +126,22 @@ describe('CircularBuffer', function() {
     assert.strictEqual(buffer.get(3), undefined);
   });
 
+  it('peekLast should not be subject to one-off errors (#223).', function() {
+    var buffer = new CircularBuffer(Array, 2);
+
+    buffer.push(true);
+    buffer.push(true);
+    buffer.push(true);
+
+    buffer.push(false);
+    buffer.push(true);
+
+    assert.deepStrictEqual(buffer.toArray(), [false, true]);
+    assert.strictEqual(buffer.peekFirst(), false);
+    assert.strictEqual(buffer.peekLast(), true);
+    assert.strictEqual(buffer.get(1), true);
+  });
+
   it('should be possible to pop the buffer.', function() {
     var buffer = new CircularBuffer(Array, 3);