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optimisation/avoid negative index lookups #407

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Run-time Optimisation

The thread.stackFrames array is accessed all the time to retrieve the
'parent' stack frame. This is done using as index of [this.stack.length
- 1]. However, a lot of the time this evaluated to [-1]. Although this
results in null, which is fine, to get to this javascript actually
defers from a numeric array lookup to an object lookup using the string
"-1". This is roughly 100 times slower to compute and so a simple catch
for negative indexes is well worth the extra check.
This commit is contained in:
griffpatch 2017-01-28 14:38:13 +00:00
parent 6f8eaaa101
commit a25e117412
1 changed files with 3 additions and 4 deletions
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7
src/engine/thread.js
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@ -101,7 +101,6 @@ Thread.prototype.pushStack = function (blockId) {
if (this.stack.length > this.stackFrames.length) { if (this.stack.length > this.stackFrames.length) {
// Copy warp mode from any higher level. // Copy warp mode from any higher level.
var warpMode = false; var warpMode = false;
if (this.stackFrames[this.stackFrames.length - 1]) {
warpMode = this.stackFrames[this.stackFrames.length - 1].warpMode; warpMode = this.stackFrames[this.stackFrames.length - 1].warpMode;
} }
this.stackFrames.push({ this.stackFrames.push({
@ -129,7 +128,7 @@ Thread.prototype.popStack = function () {
* @return {?string} Block ID on top of stack. * @return {?string} Block ID on top of stack.
*/ */
Thread.prototype.peekStack = function () { Thread.prototype.peekStack = function () {
return this.stack[this.stack.length - 1]; return this.stack.length > 0 ? this.stack[this.stack.length - 1] : null;
}; };
@ -138,7 +137,7 @@ Thread.prototype.peekStack = function () {
* @return {?Object} Last stack frame stored on this thread. * @return {?Object} Last stack frame stored on this thread.
*/ */
Thread.prototype.peekStackFrame = function () { Thread.prototype.peekStackFrame = function () {
return this.stackFrames[this.stackFrames.length - 1]; return this.stackFrames.length > 0 ? this.stackFrames[this.stackFrames.length - 1] : null;
}; };
/** /**
@ -146,7 +145,7 @@ Thread.prototype.peekStackFrame = function () {
* @return {?Object} Second to last stack frame stored on this thread. * @return {?Object} Second to last stack frame stored on this thread.
*/ */
Thread.prototype.peekParentStackFrame = function () { Thread.prototype.peekParentStackFrame = function () {
return this.stackFrames[this.stackFrames.length - 2]; return this.stackFrames.length > 1 ? this.stackFrames[this.stackFrames.length - 2] : null;
}; };
/** /**